Influence of rearing temperature and feed format in the development of the pendulous crop in broilers

Influence of rearing temperature and feed format in the development of the pendulous crop in... ABSTRACT The pendulous crop is characterized by excessive distension of the crop musculature, compromising the bird's productivity and welfare. The etiology is still unknown, but it is believed that factors related to the birds’ handling might be related to its incidence. The study was conducted in 2 environmental chambers. One was maintained at a comfortable temperature, while the other was set at a much lower temperature. In each chamber, animals were divided into 16 experimental pens (8 received mash feed and the others received pelletized feed) with a density of 12 birds/m2 (an expected stocking density of 32–36 kg/m2 after 42 d). The effects of rearing temperatures were evaluated in terms of broiler performance, specifically weight gain (kg), feed intake (kg), weekly feed intake (kg/wk), and feed conversion (kgfeed/kggrowth). The occurrences of pendulous crop were quantified every 2 d after the 14th day of rearing. Birds grown in thermal comfort and fed a pelletized ration were most susceptible (12%) to pendulous crop, followed by birds fed pelletized feed and reared in cold conditions (6.8%), and birds given mashed feed and reared at either temperature (about 3%). We concluded that feeding pelleted feed combined with warmer rearing temperatures may have caused some alteration of the gastrointestinal system of birds, which caused pendulous crop to be more prevalent. INTRODUCTION In recent years, the global chicken production has grown significantly. According to the United States Department of Agriculture (USDA, 2018), the projected world chicken meat production in 2018 is 92.5 million tones (processed weight). Pym (2013) emphasized that the growth of poultry production has only been possible due to the advances in science that have enabled the production of birds with greater genetic growth potential coupled with better feed conversion (FC), being that according to Chambers et al. (1994), feed consumption is a very representative part of the selection process. For Rosario et al. (2004), these high growth rates make the birds more prone to physiological dysfunctions, possibly compromising health and productivity. The pendulous crop is a complex condition which affects turkeys and chickens, appearing as a musculature distension of the crop. Hinshaw and Asmundson (1936) defined the pendulous crop as an abnormality characterized by temporary or permanent distension of the crop, with liquid or semi-liquid content. There are very few studies of pendulous crop, with a majority of these studies directed to the production of turkeys. The published research indicates that several factors can be linked to the development of pendulous crop in turkeys, including genetics (Hinshaw and Asmundson, 1936), nutritional factors (Wheeler et al., 1960), breeding temperature (Albuquerque et al., 1978), and lighting program (Vermette et al., 2016). In 2014 and 2015, there was an increase in the pendulous crop incidence within Brazilian broiler flocks (Ebilng et al., 2015; Santos, 2015; Globo Rural, 2014). Ebling et al. (2015) reported an incidence of 9.5% of pendulous crop in broilers at an experimental farm in the state of Rio Grande do Sul (Southern Brazil) which triggered significant concern among producers. In addition to the direct losses due to reduced production, a pendulous crop may result in carcass condemnation at slaughter. Herenda and Franco (1996) indicated that carcass contamination by contents of a pendulous crop can be worse than contamination by feces. Nery (2016) emphasized that a minimum of 4 h of fasting must be allowed before slaughter to avoid contamination by intestinal contents in the evisceration process. In previous unpublished studies, we observed that even after 12 h of fasting, birds affected with the pendulous crop retained a large amount of feed in the crop, representing a significant risk of carcass contamination at the time of slaughter. Several studies have shown that feed processing has a direct effect on the development of the bird's gastrointestinal system (Engberg et al., 2002; Svihus et al., 2010; Svihus, 2014; Truong et al., 2017). Specifically, Svihus (2014) showed that birds consuming pelleted feed had better production traits (feed intake [FI], weight gain [WG], and FC), but tended to have small and under-developed gizzard, which can affect feed passage. Given our current understanding, it is not clear whether the format of the feed can contribute to the development of pendulous crop in broilers. The etiology of the problem is not well understood; however, it is believed that its prevalence may be linked to production practices. There is no known treatment, highlighting the need for additional research into the etiology and practices that can reduce occurrence of pendulous crop. In response to this need, an experiment was designed to study the effect of rearing temperature (cold and thermoneutral) and feed format (pelleted and mashed) on the development of pendulous crop in broilers. MATERIAL AND METHODS Facilities, poultry, and management The present study was conducted at São Paulo State University Jaboticabal, Brazil, using 384 males broiler chickens, from the commercial line, Cobb500 (JBS, Nuporanga, São Paulo, Brazil). The birds were randomly assigned to two climatic chambers. The conditions in one were consistent with those recommended for the lineage of chicks (Cobb, 2008) and identified as the “thermal comfort” treatment. Conditions in the second chamber were cooler than the recommended conditions and identified as the “cold temperature” treatment. Temperatures in the cold treatment were always below those in the thermal comfort treatment. Temperatures throughout both treatments are presented in Table 1. Table 1. Mean values ± standard error of mean, of temperature (°C), and relative humidity (RH, %) within the respective chambers for each experimental treatment. Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 View Large Table 1. Mean values ± standard error of mean, of temperature (°C), and relative humidity (RH, %) within the respective chambers for each experimental treatment. Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 View Large During the experimental period, the birds received water and feed ad libitum. The diet consisted of 2 types of feed (initial: 1–21 d and growth: 22–42 d), formulated following the nutritional requirements established for broilers in tropical conditions by Rostagno et al. (2011) (Table 2). The birds were raised under constant light (24 h) provided by fluorescent bulbs and vaccinated against Marek's disease, avian pox, infectious bursal disease, and Newcastle disease, according to the Cobb vaccination program. Table 2. Nutritional composition of rations fed during the different phases: initial (1–21 d of age) and growth (22–42 d of age). Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Nutrients per kilogram of diet: *From 1 to 21 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit.E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper 0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Choline 0.4 g, Growth promoter (Zinc bacitracin) 30 mg, narasin + nicarbazin.1 g, Methionine 1.68 g. **From 22 to 42 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit. E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Colina 0,6 g, Growth Promoter (avilamycin) 7.5 mg, Monensin sodium 0.1 g, Methionine 1.4 g. View Large Table 2. Nutritional composition of rations fed during the different phases: initial (1–21 d of age) and growth (22–42 d of age). Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Nutrients per kilogram of diet: *From 1 to 21 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit.E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper 0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Choline 0.4 g, Growth promoter (Zinc bacitracin) 30 mg, narasin + nicarbazin.1 g, Methionine 1.68 g. **From 22 to 42 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit. E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Colina 0,6 g, Growth Promoter (avilamycin) 7.5 mg, Monensin sodium 0.1 g, Methionine 1.4 g. View Large Experimental design The experimental design was completely randomized, with 1 experimental unit (climatic chamber) for each breeding temperature (cold and thermoneutral), and replicate pens within each chamber with 2 feed formats (pelleted and mashed). Three hundred and eighty-four chicks were randomly assigned to 2 climatic chambers (cold and thermoneutral). Birds within each chamber were further separated into 16 pens, with half the pens receiving mashed feed and the other half receiving pelletized feed. Each pen measured 0.9 × 1.2 m, having a floor area of 1 m2 and a targeted stocking density of (an expected stocking density of 32–36 kg/m2 after 42 d) kg/m2 after day 42. Feed processing Feed ingredients were crushed and mixed in equipment suitable for this purpose. Feed was mixed in large batches. Half of each batch was fed as a mashed ration, while the other half was pelletized. Pelleted feed during the first 7 d had a pellet diameter of 1.5 mm. The pellet diameter was increased to 3 mm on day 8 and to 4 mm on day 21. Performance The birds and feed were weighed weekly, with WG (kg), total FI (kg), weekly feed intake (WFI) (kg) and, subsequently, FC (kgfeed/kggain) determined. Quantification of birds with pendulous crop The quantification of birds with a pendulous crop was performed every 2 d, beginning on day 14, because the dilated crop becomes more apparent at this stage of a broiler's life. The pendulous crop identification protocol was established after evaluation of several lots of broilers in the 2-yr period leading up to this trial. The birds were evaluated individually, through observation of the volume of the crop and palpation of the same, in order to verify the consistency of the musculature (Figure 1). Birds that presented greater-than-normal muscular distension and a more flaccid crop were identified with a mark on the back or the head. After 2 d, all birds were examined again, and if a previously marked bird still presented the same crop morphology, it received another mark. A bird was determined to have a pendulous crop if its crop was distended and flaccid during three consecutive inspections. The requirement of an initial, plus 2 confirming inspections was intended to avoid any false positives, where the distended crop may have been caused in 1 day by overeating. Thus, if the bird's crop was distended in 1 inspection and normal in another, the birds were not considered to have a pendulous crop. If a bird presented a distended and flaccid crop during 3 consecutive inspections, the date of affliction was set as the first date of detection (the day of the first marking). Figure 1. View largeDownload slide (A) Normal crop chicken, (B) crop with normal dilatation due feed overconsumption (can return to normal situation), (C) pendulous crop in the beginning of the development (flaccid musculature, little consistency musculature, saccular appearance), (D) pendulous crop dysfunction (serious situation, cannot return to normal situation). Figure 1. View largeDownload slide (A) Normal crop chicken, (B) crop with normal dilatation due feed overconsumption (can return to normal situation), (C) pendulous crop in the beginning of the development (flaccid musculature, little consistency musculature, saccular appearance), (D) pendulous crop dysfunction (serious situation, cannot return to normal situation). Statistical analysis The growth data (WG, total FI, WFI, and FC) were submitted to variance analysis, considering the effect of feed format for each rearing temperature, using the Tukey’s test at 5% of significance in the SAS (Version 9.2, SAS Institute Inc., Cary, NC). To verify if the frequency of pendulous crop is related to the rearing temperature and feed format, the chi-squared test was used. A graph was drawn showing the incidence (in % of birds) of pendulous crop over the production cycle, according to the rearing temperature and feed format. The statistical model was as follows: Yijk = μ + Ti + Fj(i) + eijk, which Yijk is a Kth observation of the variables; μ = overall mean; T is the random effect of ith temperature (1,2); F is the effect of jth feed format (1,2) inside ith rearing temperature (1,2); eijk = residual effect. RESULTS AND DISCUSSION The chi-square test shows that from day 19 to 41, the pendulous crop incidence was not independent of the studied treatments (P < 0.05). The incidence pendulous crop was greater when the chickens were fed pelletized feed under both environmental conditions (Figure 2), with 12% and 6% of the birds affected under thermoneutral and cold conditions, respectively. For both environmental temperatures, 2.6% of the birds fed mashed feed presented pendulous crop. Development of pendulous crop may be associated with a number of factors, including those associated with feed format and the mechanisms of control and motility of the gastrointestinal tract. Figure 2. View largeDownload slide Incidence of a pendulous crop (%) in the different treatments. “*”indicates that according to chi-square tests the percentage of pendulous crop was not independent of treatments at days 19 to 41 (P < 0.05). Figure 2. View largeDownload slide Incidence of a pendulous crop (%) in the different treatments. “*”indicates that according to chi-square tests the percentage of pendulous crop was not independent of treatments at days 19 to 41 (P < 0.05). Weekly WG was significantly different (P < 0.05, Table 3) within the cold chamber between birds fed mashed and pelleted feed after 21, 35, and 42 d. At 21 d, chickens fed mashed feed presented a higher WG (P < 0.05) (0.934 kg) than birds fed pelleted feed (0.891 kg). However, at 35 and 42 d, birds fed the pelleted ration presented higher WG (P < 0.05) than birds fed with mashed feed, with WG of 2,440 g (pellets) and 2,299 g (mash) at 35 d and 3,113 g (pellets) and 2,971 g (mash) at 42 d. In the thermoneutral conditions, pelleted feed produced greater weekly gains at 7, 14, and 35 d. Specifically, birds fed pelleted feed had WGs of 0.132, 0.461, and 2.380 kg and those fed mashed feed had weekly gains of 0.124, 0.437, and 2.301 kg on days 7, 14, and 35, respectively. Table 3. Weight gain (kg) of poultry reared with mashed and pelleted feed under thermoneutral and cold temperature conditions. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 3. Weight gain (kg) of poultry reared with mashed and pelleted feed under thermoneutral and cold temperature conditions. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Feed format caused the accumulated FI to be significantly (P < 0.05) different at different times within the cold temperature and thermoneutral temperatures (Table 4). Under cold temperature conditions, birds had consumed more mash feed than pelleted feed at day 14 and 21, but the trend was reversed at day 35 and 42, with pelleted feed consumption being greater. Birds fed the mashed ration consumed 0.631, 1.350, 3.827, and 5.370 kg of feed, and birds fed the pelleted ration consumed 0.596, 1.230, 3.999, and 5.449 kg of feed on after days 14, 21, 35, and 42, respectively. Under thermoneutral conditions, birds fed the mashed ration had greater FI on day 21 (1.299 vs. 1.222 kg) and day 42 (5.077 vs. 4.821 kg), compared to the pelleted ration. Table 4. Accumulated feed intake (FI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold stress. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 4. Accumulated feed intake (FI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold stress. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large The WFI was affected by the feed format within the cold conditions, with WFI for mashed feed being greater than for pelleted feed during week 2 (0.472 kg vs. 0.440 kg, respectively) and week 3 (0.719 vs. 0.634 kg, respectively). The trend was reversed during the next 2 wk with WFI for pelleted feed being greater than for mashed feed during week 4 (1.297 vs. 1.170 kg, respectively) and week 5 (1.310 vs. 1.216 kg, respectively).Weekly feed intake under thermoneutral conditions was different only during the third week, with consumption of mashed feed (0.685 kg) being greater than pelleted feed (0.629 kg). Feed conversion (Table 6) was greater under cold conditions when mashed feed was fed, compared to pelleted feed, after 21 (1.444 vs. 1.380 kgfeed/kggain, respectively), 28 (1.619 vs. 1.554 kgfeed/kggain, respectively), and 42 d (1.809 vs. 1.755 kgfeed/kggain, respectively). Under thermoneutral conditions, birds fed the pelleted ration presented better FC, compared to those fed the mashed ration, after 21 (1.309 vs. 1.398 kgfeed/kggain, respectively) and 28 d (1.496 vs. 1.585 kgfeed/kggain, respectively). It was observed that the detection of pendulous crop increased rapidly in birds fed pelletized feed after 21–28 d of growth (Figure 2), while feed consumption by birds during the same period in the cold treatment (Table 5), was significantly higher (P < 0.05) when they were fed pelleted feed (1.297 kg) compared to mash feed (1.170 kg). Feed consumed by birds raised in the thermoneutral conditions did not differ between the feed types during this period, but the consumption of mashed feed (0.685 kg) was higher than that of pelleted feed (0.629 kg) during the previous week. Table 5. Weekly feed intake (WFI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 5. Weekly feed intake (WFI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large When considering FI (Table 4) and FC (Table 6) in both environmental situations (thermoneutral and cold temperature) at 28 d, FI did not differ between feed types, but birds fed the pelleted ration presented better FC. This result can be most easily explained by the better digestibility of the pelleted feed (Calet, 1965; Abdollahi and Ravindran, 2013). Table 6. Feed conversion (FC) (kgfeed/kggain) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 6. Feed conversion (FC) (kgfeed/kggain) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large According to Goodband et al. (2002), the more a grain is processed, the greater the number of particles produced, increasing the area of contact with digestive enzymes and facilitating digestion. In the gizzard, the food is crushed and reduced into smaller particles and is forwarded to the gut (Svihus, 2014). In this sense, because it is a further-processed food, the pelleted feed dissolves into smaller particles in a shorter period of time in the gizzard, resulting in a change in the intestinal flow. Selle et al. (2013) verified that mashed diets require more time for the digestion of starch in relation to pelleted diets, and according to Truong et al. (2017) the less processed the food, the slower the intestinal transit in the bird. We believe that the pelletized ration may induce some modification in the chicken gut that increases the incidence of pendulous crop. It is very difficult to know exactly how it was happed, but the researches available in the literature suggests that pelletized feed can decrease the gizzard size, and this may be directly linked to this finds. According to Svihus (2014) and Ferket (2000), the gizzard plays an important role in regulating the food flow, and its proper development is directly linked to an improvement in food motility in the bird's gastrointestinal tract. The authors emphasized that the use of feeds that do not promote development of the gizzard tends to cause problems in the regulation of the gastrointestinal flow. Svihus et al. (2010) studied the use of different types of feed and observed that forty percent of the birds fed pelleted feed presented deregulated food consumption, eating an excessive amount of food. However, the increase in consumption was not accompanied by a commensurate WG. According to the authors, the addition of structural components in the diet (peels, fibers, etc.) improved the development of the gizzard and consequently reduced problems related to deregulated food consumption. Truong et al. (2017) found that birds fed a pelleted ration had the smallest gizzard in relation to birds whose diet consisted of whole grains, and the increase in the concentration of whole grains in the diet lead to an increase in gizzard size and internal volume. According to the authors, the action of the gizzard, breaking down the structural components of the diet, makes the muscles grow. It is difficult to understand how the gizzard development may be linked to the development of pendulous crop, but we believe that the modification in the gut flow due the poor gizzard development can be linked to this. Studies have shown that the consumption of pelleted feed causes changes in the development of the birds’ gastrointestinal tract. Engberg et al. (2002), Svihus et al. (2004), and Svihus and Hetland (2001) observed a higher relative weight of the gizzard in birds fed a mashed ration in relation to birds fed a pelleted ration, demonstrating that pelleted feed results in a poorly developed gizzard. Svihus et al. (2004) also observed a greater volume of feed within the gizzard of broilers fed a mashed ration, compared to those fed pelleted rations. Savory (1979) indicated that the mechanisms of hunger and satiety control the moments in which the bird initiates and stops its feeding. Hunger exerts a greater physiological control, causing the bird to begin and continue eating, while satiety has less influence in being able to cause the bird to stop feeding. Also, according to the same author, there are indications that control of a bird's feeding is exercised by the gizzard throughout the day and by the crop at the end of the day. For Bokkers and Koene (2003), broiler chickens have a deficiency in the satiety mechanism, and there are indications that birds of fast-growing strains feed until they reach their maximum physical capacity. In previous unpublished studies, birds affected by the pendulous crop presented heavier crops (full and empty), more feed stored in the crop, lighter empty gizzards, less gizzard content, and shorter and lighter gastrointestinal tracts as a whole. According to Svihus (2014), the use of the crop can be influenced by the lighting program, because the birds tend to store feed at the end of the light period, and the food is digested gradually during the time in which the bird remains in the dark. Svihus (2014) explained that birds raised under continuous light tend to eat smaller meals more often during the day, and filling the gizzard seems to be responsible for the feeling of satiety. Nielsen (2004) showed that birds with ad libitum feeding will not use the total capacity of food storage in the crop. Given that the lighting program adopted in this experiment was continuous light and feed was available ad libitum, the feed consumption of the birds was likely related to the filling of the gizzard. By placing the data in this research into the context of published literature, it is clear that the pelleted ration influenced the development of the pendulous crops. Scientific literature in this field is limited, and it is difficult to know for sure the mechanisms underlying this observation. Owings and Sell (1982) found that birds that received more fat in the diet had a higher incidence of the pendulous crop than the birds that received a standard diet. Svihus and Hetland (2001) found that pelleted feed passes easily through the gizzard and may cause an overload of starch in the intestines of poultry when compared to the mashed feed. Wheeler et al. (1960) studied the effects of replacing starch in the turkeys’ diet by glucose monohydrate and showed that all birds were afflicted by the pendulous crop, while none of the birds fed a conventional diet were affected. The authors highlighted the importance of nutritional factors in the development of the pendulous crop, because glucose monohydrate requires less digestion time in relation to the use of common sources of starch, which can cause an energetic overload to the organism. According to Hinshaw and Asmundson (1936), birds that develop the pendulous crop have some genetic predisposition, which may or may not develop. Asmundson and Hinshaw (1938) when studying the effect of crossing birds with and without pendulous crop found an incidence of 25% of the pendulous crop in chicks whose parents did not present the problem and 100% incidence for birds whose parents had the problem. When we compare chickens fed pelleted ration, it is possible to see that the incidence of pendulous crop was higher under thermoneutral temperature (12%) than under colder conditions (6%). Hinshaw and Asmundson (1936), when studying the effects of rearing temperature on the development of pendulous crop in turkeys, found that turkeys reared in warmer conditions had a higher incidence of the pendulous crop than turkeys reared in colder conditions. The authors also showed that birds raised in warmer environments consumed more water, which aggravated the development of the pendulous crop. Albuquerque et al. (1978) found a low incidence of the pendulous crop (2.4% of males and 7.2% of females) in turkeys raised at low temperatures (mean of 26.7°C), but when the mean temperature rose to 35°C, the incidence of the pendulous crop increased to 5.3% for males and 11.5% for females. Information available in the published literature and in this study suggests that a pelleted diet results in an under-developed gastrointestinal system and an energetic overload due to the more easily digested feed. Management practices have lead to a poorly developed and overloaded gastrointestinal system. Because the satiety of the bird is linked to the filling of the gizzard (Savory, 1979), and the pelleted feed has a low retention time, the bird starts to ingest a greater amount of feed and cause an even greater burden on the gastrointestinal system. A bird raised entirely on pelleted feed will have an under-developed gastrointestinal system, and when it starts to ingest larger volumes of feed (growth phase, 21 to 42 d of age), the bird is unable to cope with the greater amounts of nutritional energy. The energy overload seems to deregulate the organism, causing food to be constantly stored in the crop. The crop expands, stretching the muscles, losing the capacity to contract and empty, until it reaches a point where the damage is irreversible. During this research, 1 bird died due to the rupture of its overly distended crop. The bird in question had an extremely dilated crop that became increasingly distended with time. However, even with such a large amount of feed stored in the crop, the bird continued to eat until the crop burst. This seems to support Savory's (1979) statement that the satiety of the bird is more related to the filling of the gizzard than to the filling of the crop. In the case of a pendulous crop, feed is not easily transferred from the crop to the gizzard, and the bird is unable to regulate food intake, causing further dysfunction within the gastrointestinal tract of the bird. CONCLUSIONS Feeding a pelleted ration increased the incidence of pendulous crop in broilers, and this feed may have caused some alteration of the gastrointestinal system of birds, which caused pendulous crop to be more prevalent, and the incidence of the pendulous crop was more strongly associated with higher temperatures. Further studies are needed to clarify the causes and effects of the pendulous crop in the bird, such as changes in the gastrointestinal tract (size, motility, functionality) and ingestive behavior, among others. SUPPLEMENTARY DATA Supplementary data are available at Poultry Science online. ACKNOWLEDGMENTS The authors are thankful to Cobb-Vantress for all the support given for this research. REFERENCES Abdollahi M. R. , Ravindran V. . 2013 . Influence of pellet length on pellet quality and performance of broiler starters . J. Appl. Poult. Res. 22 : 516 – 522 . Google Scholar CrossRef Search ADS Albuquerque K. , Leighton A. T. Jr , Mason J. P. Jr. , Potter L. 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Sci. 95 : 985 – 996 . Google Scholar CrossRef Search ADS PubMed Wheeler H. O. , Reid B. L. , Ferguson T. M. , Couch J. R. , Rigdon R. H. . 1960 . Differences in susceptibility of broad breasted bronze and beltsville small white turkeys to dietary-induced pendulous crop . Poult. Sci. 39 : 263 – 267 . Google Scholar CrossRef Search ADS © 2018 Poultry Science Association Inc. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Poultry Science Oxford University Press

Influence of rearing temperature and feed format in the development of the pendulous crop in broilers

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Oxford University Press
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© 2018 Poultry Science Association Inc.
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0032-5791
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1525-3171
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10.3382/ps/pey221
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Abstract

ABSTRACT The pendulous crop is characterized by excessive distension of the crop musculature, compromising the bird's productivity and welfare. The etiology is still unknown, but it is believed that factors related to the birds’ handling might be related to its incidence. The study was conducted in 2 environmental chambers. One was maintained at a comfortable temperature, while the other was set at a much lower temperature. In each chamber, animals were divided into 16 experimental pens (8 received mash feed and the others received pelletized feed) with a density of 12 birds/m2 (an expected stocking density of 32–36 kg/m2 after 42 d). The effects of rearing temperatures were evaluated in terms of broiler performance, specifically weight gain (kg), feed intake (kg), weekly feed intake (kg/wk), and feed conversion (kgfeed/kggrowth). The occurrences of pendulous crop were quantified every 2 d after the 14th day of rearing. Birds grown in thermal comfort and fed a pelletized ration were most susceptible (12%) to pendulous crop, followed by birds fed pelletized feed and reared in cold conditions (6.8%), and birds given mashed feed and reared at either temperature (about 3%). We concluded that feeding pelleted feed combined with warmer rearing temperatures may have caused some alteration of the gastrointestinal system of birds, which caused pendulous crop to be more prevalent. INTRODUCTION In recent years, the global chicken production has grown significantly. According to the United States Department of Agriculture (USDA, 2018), the projected world chicken meat production in 2018 is 92.5 million tones (processed weight). Pym (2013) emphasized that the growth of poultry production has only been possible due to the advances in science that have enabled the production of birds with greater genetic growth potential coupled with better feed conversion (FC), being that according to Chambers et al. (1994), feed consumption is a very representative part of the selection process. For Rosario et al. (2004), these high growth rates make the birds more prone to physiological dysfunctions, possibly compromising health and productivity. The pendulous crop is a complex condition which affects turkeys and chickens, appearing as a musculature distension of the crop. Hinshaw and Asmundson (1936) defined the pendulous crop as an abnormality characterized by temporary or permanent distension of the crop, with liquid or semi-liquid content. There are very few studies of pendulous crop, with a majority of these studies directed to the production of turkeys. The published research indicates that several factors can be linked to the development of pendulous crop in turkeys, including genetics (Hinshaw and Asmundson, 1936), nutritional factors (Wheeler et al., 1960), breeding temperature (Albuquerque et al., 1978), and lighting program (Vermette et al., 2016). In 2014 and 2015, there was an increase in the pendulous crop incidence within Brazilian broiler flocks (Ebilng et al., 2015; Santos, 2015; Globo Rural, 2014). Ebling et al. (2015) reported an incidence of 9.5% of pendulous crop in broilers at an experimental farm in the state of Rio Grande do Sul (Southern Brazil) which triggered significant concern among producers. In addition to the direct losses due to reduced production, a pendulous crop may result in carcass condemnation at slaughter. Herenda and Franco (1996) indicated that carcass contamination by contents of a pendulous crop can be worse than contamination by feces. Nery (2016) emphasized that a minimum of 4 h of fasting must be allowed before slaughter to avoid contamination by intestinal contents in the evisceration process. In previous unpublished studies, we observed that even after 12 h of fasting, birds affected with the pendulous crop retained a large amount of feed in the crop, representing a significant risk of carcass contamination at the time of slaughter. Several studies have shown that feed processing has a direct effect on the development of the bird's gastrointestinal system (Engberg et al., 2002; Svihus et al., 2010; Svihus, 2014; Truong et al., 2017). Specifically, Svihus (2014) showed that birds consuming pelleted feed had better production traits (feed intake [FI], weight gain [WG], and FC), but tended to have small and under-developed gizzard, which can affect feed passage. Given our current understanding, it is not clear whether the format of the feed can contribute to the development of pendulous crop in broilers. The etiology of the problem is not well understood; however, it is believed that its prevalence may be linked to production practices. There is no known treatment, highlighting the need for additional research into the etiology and practices that can reduce occurrence of pendulous crop. In response to this need, an experiment was designed to study the effect of rearing temperature (cold and thermoneutral) and feed format (pelleted and mashed) on the development of pendulous crop in broilers. MATERIAL AND METHODS Facilities, poultry, and management The present study was conducted at São Paulo State University Jaboticabal, Brazil, using 384 males broiler chickens, from the commercial line, Cobb500 (JBS, Nuporanga, São Paulo, Brazil). The birds were randomly assigned to two climatic chambers. The conditions in one were consistent with those recommended for the lineage of chicks (Cobb, 2008) and identified as the “thermal comfort” treatment. Conditions in the second chamber were cooler than the recommended conditions and identified as the “cold temperature” treatment. Temperatures in the cold treatment were always below those in the thermal comfort treatment. Temperatures throughout both treatments are presented in Table 1. Table 1. Mean values ± standard error of mean, of temperature (°C), and relative humidity (RH, %) within the respective chambers for each experimental treatment. Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 View Large Table 1. Mean values ± standard error of mean, of temperature (°C), and relative humidity (RH, %) within the respective chambers for each experimental treatment. Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 Thermal comfort Cold temperature Period (d) Temperature (°C) RH (%) Temperature (°C) RH (%) 1–4 32.7 ± 1.03 78.5 ± 2.2 32.4 ± 1.38 76.6 ± 2.8 5–7 30.4 ± 1.12 77.3 ± 2.8 26.7 ± 0.76 72.4 ± 2.1 8–14 26.4 ± 0.56 68.2 ± 2.1 22.8 ± 0,53 54.3 ± 1.2 14–16 25.0 ± 1.05 64.2 ± 1.3 19.8 ± 0.43 61.2 ± 3,4 16–21 23.4 ± 0.53 59.4 ± 2.4 18.2 ± 0.82 56.3 ± 2.6 21–42 21.1 ± 0.65 60.1 ± 3.3 17.3 ± 1.2 58.2 ± 1.7 View Large During the experimental period, the birds received water and feed ad libitum. The diet consisted of 2 types of feed (initial: 1–21 d and growth: 22–42 d), formulated following the nutritional requirements established for broilers in tropical conditions by Rostagno et al. (2011) (Table 2). The birds were raised under constant light (24 h) provided by fluorescent bulbs and vaccinated against Marek's disease, avian pox, infectious bursal disease, and Newcastle disease, according to the Cobb vaccination program. Table 2. Nutritional composition of rations fed during the different phases: initial (1–21 d of age) and growth (22–42 d of age). Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Nutrients per kilogram of diet: *From 1 to 21 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit.E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper 0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Choline 0.4 g, Growth promoter (Zinc bacitracin) 30 mg, narasin + nicarbazin.1 g, Methionine 1.68 g. **From 22 to 42 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit. E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Colina 0,6 g, Growth Promoter (avilamycin) 7.5 mg, Monensin sodium 0.1 g, Methionine 1.4 g. View Large Table 2. Nutritional composition of rations fed during the different phases: initial (1–21 d of age) and growth (22–42 d of age). Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Ingredients (%) Initial phase* Growth phase** Corn 59.52 63.74 Soy chaff (45%) 35.15 29.79 Soy oil 1.29 3.12 Dicalcic phosphate 1.63 1.16 Limestone 0.84 0.76 Salt 0.42 0.44 L-Lysine HCL (78%) 0.25 0.21 DL-Methionine (99%) 0.29 0.23 L-Threonine 0.08 0.04 BHT 0.01 0.01 Vitamin and mineral supplement* 0.50 0.50 Total 100.00 100.00 Calculated nutritional composition Crude protein (%) 21.27 18.86 Metabolizable energy (kcal/kg) 3000 3200 Ca (%) 0.85 0.69 Na (%) 0.19 0.20 Available phosphorus (%) 0.42 0.32 Methionine+ cysteine (digestible) (%) 0.88 0.77 Methionine (digestible) (%) 0.56 0.49 Lysine (digestible) (%) 1.22 1.05 Threonine (digestible) (%) 0.79 0.68 Tryptophan (digestible) (%) 0.24 0.21 Arginine(digestible) (%) 1.32 1.16 Nutrients per kilogram of diet: *From 1 to 21 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit.E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper 0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Choline 0.4 g, Growth promoter (Zinc bacitracin) 30 mg, narasin + nicarbazin.1 g, Methionine 1.68 g. **From 22 to 42 d of age—Vit. A 7.000 U.I., Vit. D3 3.000 U.I., Vit. E 25 U.I., Vit. K 0.98 mg, Vit. B1 1.78 mg, Vit. B2 9.6 mg, Vit. B6 3.5 mg, Vit. B12 10 μg, Folic acid 0.57 mg, Biotin 0.16 mg, Niacin 34.5 mg, Calcium pantothenate 9.8 mg, Copper0.12 g, Cobalt 0.02 mg, Iodo 1.3 mg, Iron 0.05 g, Manganese 0.07 g, Zinc 0.09 mg, Zinc oxide 6.75 mg, Selenium 0.27 mg, Colina 0,6 g, Growth Promoter (avilamycin) 7.5 mg, Monensin sodium 0.1 g, Methionine 1.4 g. View Large Experimental design The experimental design was completely randomized, with 1 experimental unit (climatic chamber) for each breeding temperature (cold and thermoneutral), and replicate pens within each chamber with 2 feed formats (pelleted and mashed). Three hundred and eighty-four chicks were randomly assigned to 2 climatic chambers (cold and thermoneutral). Birds within each chamber were further separated into 16 pens, with half the pens receiving mashed feed and the other half receiving pelletized feed. Each pen measured 0.9 × 1.2 m, having a floor area of 1 m2 and a targeted stocking density of (an expected stocking density of 32–36 kg/m2 after 42 d) kg/m2 after day 42. Feed processing Feed ingredients were crushed and mixed in equipment suitable for this purpose. Feed was mixed in large batches. Half of each batch was fed as a mashed ration, while the other half was pelletized. Pelleted feed during the first 7 d had a pellet diameter of 1.5 mm. The pellet diameter was increased to 3 mm on day 8 and to 4 mm on day 21. Performance The birds and feed were weighed weekly, with WG (kg), total FI (kg), weekly feed intake (WFI) (kg) and, subsequently, FC (kgfeed/kggain) determined. Quantification of birds with pendulous crop The quantification of birds with a pendulous crop was performed every 2 d, beginning on day 14, because the dilated crop becomes more apparent at this stage of a broiler's life. The pendulous crop identification protocol was established after evaluation of several lots of broilers in the 2-yr period leading up to this trial. The birds were evaluated individually, through observation of the volume of the crop and palpation of the same, in order to verify the consistency of the musculature (Figure 1). Birds that presented greater-than-normal muscular distension and a more flaccid crop were identified with a mark on the back or the head. After 2 d, all birds were examined again, and if a previously marked bird still presented the same crop morphology, it received another mark. A bird was determined to have a pendulous crop if its crop was distended and flaccid during three consecutive inspections. The requirement of an initial, plus 2 confirming inspections was intended to avoid any false positives, where the distended crop may have been caused in 1 day by overeating. Thus, if the bird's crop was distended in 1 inspection and normal in another, the birds were not considered to have a pendulous crop. If a bird presented a distended and flaccid crop during 3 consecutive inspections, the date of affliction was set as the first date of detection (the day of the first marking). Figure 1. View largeDownload slide (A) Normal crop chicken, (B) crop with normal dilatation due feed overconsumption (can return to normal situation), (C) pendulous crop in the beginning of the development (flaccid musculature, little consistency musculature, saccular appearance), (D) pendulous crop dysfunction (serious situation, cannot return to normal situation). Figure 1. View largeDownload slide (A) Normal crop chicken, (B) crop with normal dilatation due feed overconsumption (can return to normal situation), (C) pendulous crop in the beginning of the development (flaccid musculature, little consistency musculature, saccular appearance), (D) pendulous crop dysfunction (serious situation, cannot return to normal situation). Statistical analysis The growth data (WG, total FI, WFI, and FC) were submitted to variance analysis, considering the effect of feed format for each rearing temperature, using the Tukey’s test at 5% of significance in the SAS (Version 9.2, SAS Institute Inc., Cary, NC). To verify if the frequency of pendulous crop is related to the rearing temperature and feed format, the chi-squared test was used. A graph was drawn showing the incidence (in % of birds) of pendulous crop over the production cycle, according to the rearing temperature and feed format. The statistical model was as follows: Yijk = μ + Ti + Fj(i) + eijk, which Yijk is a Kth observation of the variables; μ = overall mean; T is the random effect of ith temperature (1,2); F is the effect of jth feed format (1,2) inside ith rearing temperature (1,2); eijk = residual effect. RESULTS AND DISCUSSION The chi-square test shows that from day 19 to 41, the pendulous crop incidence was not independent of the studied treatments (P < 0.05). The incidence pendulous crop was greater when the chickens were fed pelletized feed under both environmental conditions (Figure 2), with 12% and 6% of the birds affected under thermoneutral and cold conditions, respectively. For both environmental temperatures, 2.6% of the birds fed mashed feed presented pendulous crop. Development of pendulous crop may be associated with a number of factors, including those associated with feed format and the mechanisms of control and motility of the gastrointestinal tract. Figure 2. View largeDownload slide Incidence of a pendulous crop (%) in the different treatments. “*”indicates that according to chi-square tests the percentage of pendulous crop was not independent of treatments at days 19 to 41 (P < 0.05). Figure 2. View largeDownload slide Incidence of a pendulous crop (%) in the different treatments. “*”indicates that according to chi-square tests the percentage of pendulous crop was not independent of treatments at days 19 to 41 (P < 0.05). Weekly WG was significantly different (P < 0.05, Table 3) within the cold chamber between birds fed mashed and pelleted feed after 21, 35, and 42 d. At 21 d, chickens fed mashed feed presented a higher WG (P < 0.05) (0.934 kg) than birds fed pelleted feed (0.891 kg). However, at 35 and 42 d, birds fed the pelleted ration presented higher WG (P < 0.05) than birds fed with mashed feed, with WG of 2,440 g (pellets) and 2,299 g (mash) at 35 d and 3,113 g (pellets) and 2,971 g (mash) at 42 d. In the thermoneutral conditions, pelleted feed produced greater weekly gains at 7, 14, and 35 d. Specifically, birds fed pelleted feed had WGs of 0.132, 0.461, and 2.380 kg and those fed mashed feed had weekly gains of 0.124, 0.437, and 2.301 kg on days 7, 14, and 35, respectively. Table 3. Weight gain (kg) of poultry reared with mashed and pelleted feed under thermoneutral and cold temperature conditions. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 3. Weight gain (kg) of poultry reared with mashed and pelleted feed under thermoneutral and cold temperature conditions. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WG7 0.126 ± 0.0017 0.127 ± 0.0018 0.6684 0.124 ± 0.0016b 0.132 ± 0.0017a 0.0308 WG14 0.463 ± 0.0035 0.457 ± 0.0041 0.1468 0.437 ± 0.0066b 0.461 ± 0.0036a 0.0182 WG21 0.934 ± 0.0087a 0.891 ± 0.0083b 0.0079 0.930 ± 0.0151 0.933 ± 0.0092 0.8637 WG28 1.569 ± 0.0313 1.646 ± 0.0171 0.0744 1.591 ± 0.0255 1.638 ± 0.0198 0.1539 WG35 2.299 ± 0.0369b 2.440 ± 0.0289a 0.0371 2.301 ± 0.0228b 2.380 ± 0.0292a 0.0271 WG42 2.971 ± 0.0243b 3.113 ± 0.0209a 0.0026 2.944 ± 0.0423 2.886 ± 0.0445 0.1189 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Feed format caused the accumulated FI to be significantly (P < 0.05) different at different times within the cold temperature and thermoneutral temperatures (Table 4). Under cold temperature conditions, birds had consumed more mash feed than pelleted feed at day 14 and 21, but the trend was reversed at day 35 and 42, with pelleted feed consumption being greater. Birds fed the mashed ration consumed 0.631, 1.350, 3.827, and 5.370 kg of feed, and birds fed the pelleted ration consumed 0.596, 1.230, 3.999, and 5.449 kg of feed on after days 14, 21, 35, and 42, respectively. Under thermoneutral conditions, birds fed the mashed ration had greater FI on day 21 (1.299 vs. 1.222 kg) and day 42 (5.077 vs. 4.821 kg), compared to the pelleted ration. Table 4. Accumulated feed intake (FI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold stress. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 4. Accumulated feed intake (FI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold stress. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FI7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 FI14 0.631 ± 0.0113a 0.596 ± 0.0103b 0.0470 0.602 ± 0.0205 0.593 ± 0.0073 0.6956 FI21 1.350 ± 0.0195a 1.230 ± 0.0164b 0.0024 1.299 ± 0.0189a 1.222 ± 0.0127b 0.0046 FI28 2.533 ± 0.0218 2.527 ± 0.0299 0.8159 2.521 ± 0.0419 2.453 ± 0.0252 0.2048 FI35 3.827 ± 0.0643b 3.999 ± 0.0575a 0.0395 3.709 ± 0.0242 3.697 ± 0.0295 0.7635 FI42 5.370 ± 0.0620b 5.440 ± 0.0710a 0.0497 5.077 ± 0.0898a 4.821 ± 0.0247b 0.0247 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large The WFI was affected by the feed format within the cold conditions, with WFI for mashed feed being greater than for pelleted feed during week 2 (0.472 kg vs. 0.440 kg, respectively) and week 3 (0.719 vs. 0.634 kg, respectively). The trend was reversed during the next 2 wk with WFI for pelleted feed being greater than for mashed feed during week 4 (1.297 vs. 1.170 kg, respectively) and week 5 (1.310 vs. 1.216 kg, respectively).Weekly feed intake under thermoneutral conditions was different only during the third week, with consumption of mashed feed (0.685 kg) being greater than pelleted feed (0.629 kg). Feed conversion (Table 6) was greater under cold conditions when mashed feed was fed, compared to pelleted feed, after 21 (1.444 vs. 1.380 kgfeed/kggain, respectively), 28 (1.619 vs. 1.554 kgfeed/kggain, respectively), and 42 d (1.809 vs. 1.755 kgfeed/kggain, respectively). Under thermoneutral conditions, birds fed the pelleted ration presented better FC, compared to those fed the mashed ration, after 21 (1.309 vs. 1.398 kgfeed/kggain, respectively) and 28 d (1.496 vs. 1.585 kgfeed/kggain, respectively). It was observed that the detection of pendulous crop increased rapidly in birds fed pelletized feed after 21–28 d of growth (Figure 2), while feed consumption by birds during the same period in the cold treatment (Table 5), was significantly higher (P < 0.05) when they were fed pelleted feed (1.297 kg) compared to mash feed (1.170 kg). Feed consumed by birds raised in the thermoneutral conditions did not differ between the feed types during this period, but the consumption of mashed feed (0.685 kg) was higher than that of pelleted feed (0.629 kg) during the previous week. Table 5. Weekly feed intake (WFI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 5. Weekly feed intake (WFI) (kg) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value WFI 1–7 0.158 ± 0.0038 0.157 ± 0.0031 0.8913 0.151 ± 0.0059 0.161 ± 0.0052 0.2136 WFI 7–14 0.472 ± 0.0117a 0.440 ± 0.0084b 0.0498 0.449 ± 0.0148 0.432 ± 0.0052 0.3488 WFI 14–21 0.719 ± 0.0124a 0.634 ± 0.0087b 0.0018 0.685 ± 0.0112a 0.629 ± 0.0087b 0.0068 WFI 21–28 1.170 ± 0.0153b 1.297 ± 0.0162a 0.0006 1.190 ± 0.0195 1.204 ± 0.0147 0.5901 WFI 28–35 1.216 ± 0.0200b 1.310 ± 0.0178a 0.0032 1.161 ± 0.0108 1.190 ± 0.0361 0.5209 WFI 35–42 1.410 ± 0.0407 1.370 ± 0.0256 0.3670 1.326 ± 0.0579 1.162 ± 0.0704 0.0992 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large When considering FI (Table 4) and FC (Table 6) in both environmental situations (thermoneutral and cold temperature) at 28 d, FI did not differ between feed types, but birds fed the pelleted ration presented better FC. This result can be most easily explained by the better digestibility of the pelleted feed (Calet, 1965; Abdollahi and Ravindran, 2013). Table 6. Feed conversion (FC) (kgfeed/kggain) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large Table 6. Feed conversion (FC) (kgfeed/kggain) of poultry reared with mashed and pelleted feed in a thermal comfort situation and cold temperature. Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Cold temperature Thermal comfort Mash Pellet P value Mash Pellet P value FC7 1.245 ± 0.0259 1.233 ± 0.0354 0.8295 1.217 ± 0.0387 1.222 ± 0.0283 0.8846 FC14 1.364 ± 0.0235 1.303 ± 0.0196 0.0768 1.378 ± 0.0386 1.288 ± 0.0163 0.0530 FC21 1.444 ± 0.0118b 1.380 ± 0.0098a 0.0028 1.398 ± 0.0225b 1.309 ± 0.0081a 0.0065 FC28 1.619 ± 0.0250b 1.554 ± 0.0070a 0.0223 1.585 ± 0.0206b 1.496 ± 0.0137a 0.0157 FC35 1.665 ± 0.0247 1.640 ± 0.0191 0.4356 1.612 ± 0.0126 1.555 ± 0.0256 0.0656 FC42 1.809 ± 0.0246b 1.755 ± 0.0212a 0.0126 1.724 ± 0.0113 1.673 ± 0.0247 0.1296 Different lower case letters indicate significant differences in the row, within each temperature treatment, using Tukey's test at 5% significance. View Large According to Goodband et al. (2002), the more a grain is processed, the greater the number of particles produced, increasing the area of contact with digestive enzymes and facilitating digestion. In the gizzard, the food is crushed and reduced into smaller particles and is forwarded to the gut (Svihus, 2014). In this sense, because it is a further-processed food, the pelleted feed dissolves into smaller particles in a shorter period of time in the gizzard, resulting in a change in the intestinal flow. Selle et al. (2013) verified that mashed diets require more time for the digestion of starch in relation to pelleted diets, and according to Truong et al. (2017) the less processed the food, the slower the intestinal transit in the bird. We believe that the pelletized ration may induce some modification in the chicken gut that increases the incidence of pendulous crop. It is very difficult to know exactly how it was happed, but the researches available in the literature suggests that pelletized feed can decrease the gizzard size, and this may be directly linked to this finds. According to Svihus (2014) and Ferket (2000), the gizzard plays an important role in regulating the food flow, and its proper development is directly linked to an improvement in food motility in the bird's gastrointestinal tract. The authors emphasized that the use of feeds that do not promote development of the gizzard tends to cause problems in the regulation of the gastrointestinal flow. Svihus et al. (2010) studied the use of different types of feed and observed that forty percent of the birds fed pelleted feed presented deregulated food consumption, eating an excessive amount of food. However, the increase in consumption was not accompanied by a commensurate WG. According to the authors, the addition of structural components in the diet (peels, fibers, etc.) improved the development of the gizzard and consequently reduced problems related to deregulated food consumption. Truong et al. (2017) found that birds fed a pelleted ration had the smallest gizzard in relation to birds whose diet consisted of whole grains, and the increase in the concentration of whole grains in the diet lead to an increase in gizzard size and internal volume. According to the authors, the action of the gizzard, breaking down the structural components of the diet, makes the muscles grow. It is difficult to understand how the gizzard development may be linked to the development of pendulous crop, but we believe that the modification in the gut flow due the poor gizzard development can be linked to this. Studies have shown that the consumption of pelleted feed causes changes in the development of the birds’ gastrointestinal tract. Engberg et al. (2002), Svihus et al. (2004), and Svihus and Hetland (2001) observed a higher relative weight of the gizzard in birds fed a mashed ration in relation to birds fed a pelleted ration, demonstrating that pelleted feed results in a poorly developed gizzard. Svihus et al. (2004) also observed a greater volume of feed within the gizzard of broilers fed a mashed ration, compared to those fed pelleted rations. Savory (1979) indicated that the mechanisms of hunger and satiety control the moments in which the bird initiates and stops its feeding. Hunger exerts a greater physiological control, causing the bird to begin and continue eating, while satiety has less influence in being able to cause the bird to stop feeding. Also, according to the same author, there are indications that control of a bird's feeding is exercised by the gizzard throughout the day and by the crop at the end of the day. For Bokkers and Koene (2003), broiler chickens have a deficiency in the satiety mechanism, and there are indications that birds of fast-growing strains feed until they reach their maximum physical capacity. In previous unpublished studies, birds affected by the pendulous crop presented heavier crops (full and empty), more feed stored in the crop, lighter empty gizzards, less gizzard content, and shorter and lighter gastrointestinal tracts as a whole. According to Svihus (2014), the use of the crop can be influenced by the lighting program, because the birds tend to store feed at the end of the light period, and the food is digested gradually during the time in which the bird remains in the dark. Svihus (2014) explained that birds raised under continuous light tend to eat smaller meals more often during the day, and filling the gizzard seems to be responsible for the feeling of satiety. Nielsen (2004) showed that birds with ad libitum feeding will not use the total capacity of food storage in the crop. Given that the lighting program adopted in this experiment was continuous light and feed was available ad libitum, the feed consumption of the birds was likely related to the filling of the gizzard. By placing the data in this research into the context of published literature, it is clear that the pelleted ration influenced the development of the pendulous crops. Scientific literature in this field is limited, and it is difficult to know for sure the mechanisms underlying this observation. Owings and Sell (1982) found that birds that received more fat in the diet had a higher incidence of the pendulous crop than the birds that received a standard diet. Svihus and Hetland (2001) found that pelleted feed passes easily through the gizzard and may cause an overload of starch in the intestines of poultry when compared to the mashed feed. Wheeler et al. (1960) studied the effects of replacing starch in the turkeys’ diet by glucose monohydrate and showed that all birds were afflicted by the pendulous crop, while none of the birds fed a conventional diet were affected. The authors highlighted the importance of nutritional factors in the development of the pendulous crop, because glucose monohydrate requires less digestion time in relation to the use of common sources of starch, which can cause an energetic overload to the organism. According to Hinshaw and Asmundson (1936), birds that develop the pendulous crop have some genetic predisposition, which may or may not develop. Asmundson and Hinshaw (1938) when studying the effect of crossing birds with and without pendulous crop found an incidence of 25% of the pendulous crop in chicks whose parents did not present the problem and 100% incidence for birds whose parents had the problem. When we compare chickens fed pelleted ration, it is possible to see that the incidence of pendulous crop was higher under thermoneutral temperature (12%) than under colder conditions (6%). Hinshaw and Asmundson (1936), when studying the effects of rearing temperature on the development of pendulous crop in turkeys, found that turkeys reared in warmer conditions had a higher incidence of the pendulous crop than turkeys reared in colder conditions. The authors also showed that birds raised in warmer environments consumed more water, which aggravated the development of the pendulous crop. Albuquerque et al. (1978) found a low incidence of the pendulous crop (2.4% of males and 7.2% of females) in turkeys raised at low temperatures (mean of 26.7°C), but when the mean temperature rose to 35°C, the incidence of the pendulous crop increased to 5.3% for males and 11.5% for females. Information available in the published literature and in this study suggests that a pelleted diet results in an under-developed gastrointestinal system and an energetic overload due to the more easily digested feed. Management practices have lead to a poorly developed and overloaded gastrointestinal system. Because the satiety of the bird is linked to the filling of the gizzard (Savory, 1979), and the pelleted feed has a low retention time, the bird starts to ingest a greater amount of feed and cause an even greater burden on the gastrointestinal system. A bird raised entirely on pelleted feed will have an under-developed gastrointestinal system, and when it starts to ingest larger volumes of feed (growth phase, 21 to 42 d of age), the bird is unable to cope with the greater amounts of nutritional energy. The energy overload seems to deregulate the organism, causing food to be constantly stored in the crop. The crop expands, stretching the muscles, losing the capacity to contract and empty, until it reaches a point where the damage is irreversible. During this research, 1 bird died due to the rupture of its overly distended crop. The bird in question had an extremely dilated crop that became increasingly distended with time. However, even with such a large amount of feed stored in the crop, the bird continued to eat until the crop burst. This seems to support Savory's (1979) statement that the satiety of the bird is more related to the filling of the gizzard than to the filling of the crop. In the case of a pendulous crop, feed is not easily transferred from the crop to the gizzard, and the bird is unable to regulate food intake, causing further dysfunction within the gastrointestinal tract of the bird. CONCLUSIONS Feeding a pelleted ration increased the incidence of pendulous crop in broilers, and this feed may have caused some alteration of the gastrointestinal system of birds, which caused pendulous crop to be more prevalent, and the incidence of the pendulous crop was more strongly associated with higher temperatures. Further studies are needed to clarify the causes and effects of the pendulous crop in the bird, such as changes in the gastrointestinal tract (size, motility, functionality) and ingestive behavior, among others. SUPPLEMENTARY DATA Supplementary data are available at Poultry Science online. ACKNOWLEDGMENTS The authors are thankful to Cobb-Vantress for all the support given for this research. REFERENCES Abdollahi M. R. , Ravindran V. . 2013 . Influence of pellet length on pellet quality and performance of broiler starters . J. Appl. Poult. Res. 22 : 516 – 522 . Google Scholar CrossRef Search ADS Albuquerque K. , Leighton A. T. Jr , Mason J. P. Jr. , Potter L. 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Poultry ScienceOxford University Press

Published: May 30, 2018

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