Effects of a Commercial Beta-Mannanase Product on Growth Performance, Intestinal Histomorphology, Bone and Body Composition, and Amino Acid Digestibility in White Pekin Ducks

Effects of a Commercial Beta-Mannanase Product on Growth Performance, Intestinal Histomorphology,... Abstract Two experiments were conducted to evaluate effects of a commercial β-mannanase in duck diets 1–21 d. Both experiments included 0%, 0.01%, 0.05%, 0.1%, and 0.2% of β-mannanase treatments. Experimental units of 5 birds per pen were replicated 8 times in 4 different rooms. The data were analyzed as a 2 (Experiment) × 5 (Treatment) × 8 (Replicate) factorial analysis. Body weight of all β-mannanase groups was ∼66 g and ∼79 g greater than control fed birds at day 14 and 21, respectively. All β-mannanase groups had an average of 0.1, 0.14, and 0.08 lower feed conversion than controls at day 7, 14, and 21, respectively. Productivity index increased over controls by an average of 41, 81, and 48 on day 7, 14, and 21, respectively. Illeal length of all β-mannanase groups was greater than controls, and the 0.01% and 0.05% β-mannanase groups had ∼0.66 lower ileal viscosity than controls. Ducks fed 0.10% β-mannanase had greater ileal villi height than control, 0.01%, and 0.20% β-mannanase groups. Feeding diets with 0.05%, 0.10%, and 0.20% β-mannanase resulted in greater ileal villi width compared to controls. These treatments had greater ileal crypt depth than control and 0.05% β-mannanase groups. All β-mannanase treated groups had greater amino acid digestibility than controls. β-Mannanase at 0.10% resulted in a lower percentage of fat and greater bone strength than control and 0.20% β-mannanase. This study demonstrated that addition of β-mannanase positively affects duck growth performance, gut morphology, and digestibility. DESCRIPTION OF THE PROBLEM As the use of antibiotics is prohibited in the poultry industry, researchers have specifically focused on the development of innovative alternatives to antibiotic additives in poultry diets to improve growth performance and reduce mortality. Monogastric animals, such as poultry, are not able to completely digest non-starch polysaccharides (NSPs); hence, they often require enzymes to break down β (α)-linked NSPs [1]. Corn and soybean meal are the most common main ingredients for poultry diets that contain β-mannan, which is one kind of NSPs. β-Mannan is composed of multiple mannose and glucose units in β-1,4-linkages as the backbone [2], and may also be linked to galactose residues by α-1,6-linkage [3]. β-Mannan is known to increase intestinal viscosity. The increase of intestinal viscosity can lead to reduced nutrient absorption [4] and rate of nutrient passage [5], and also impact intestinal morphology [6]. β-Mannanase inhibits the negative effects of NSPs in poultry by directly degrading the NSPs in the plant cell walls [7]. β-Mannanase is an endo-type enzyme and assists in breaking the β-mannan backbone chains. Therefore, if birds ingest the β-mannanase, it increases their growth performance by cleaving the NSPs links, which then improves nutrient digestibility. Effects of β-mannanase have already been examined through research with chickens. Mussini et al. [8] used a commercial β-mannanase product in broiler chicken diets. These authors reported that the groups treated with β-mannanase showed significantly better amino acid digestibility compared to the controls. Ayoola et al. [9] evaluated the effects of β-mannanase on enteric mucosal morphological development and adherent mucus layer thickness in turkeys. This study found that β-mannanase impacted villi morphology, surface area, and mucin thickness. Even though β-mannanase is one of the most widely used enzymes for poultry, research with β-mannanase in ducks is limited. Therefore, this study was conducted to determine the effects of β-mannanase on White Pekin ducks. Our study used 5 different concentrations of β-mannanase to determine the effects on growth performance, intestinal morphology, bone and body composition, and amino acid digestibility in Pekin ducks. MATERIALS AND METHODS Experimental Design Two identical experiments (A and B) were conducted. In each experiment, a total of 200 mixed-sex day-old ducklings were randomly housed in 40 pens with 5 birds per pen. Pens were assigned to 5 dietary treatments and arranged as 8 replicates (2 each in 4 rooms) resulting in a total of 40 ducks per dietary treatment. Birds, Housing, and Diets White Pekin duck eggs were obtained from a commercial source [10]. The eggs were incubated and hatched, and healthy ducklings were selected at the Texas A&M University Poultry Research, Teaching and Extension Center (TAMUPRC). The dietary treatments were 0.0%, 0.01%, 0.05%, 0.10%, and 0.20% commercial β-mannanase (800,000 U/kg) [11]. The diet formulations were adapted from Zeng et al. [12] with minor modifications (Table 1). In both experiments, starter (day 0–13) and grower (day 14–21) diets were mixed and pelleted at the TAMUPRC feed mill. Pen dimensions were 0.97 × 0.67 × 0.24 m, which allowed 0.03 m3/bird at placement. Each pen consisted of 1 feeder and 1 water tray and an ad libitum supply of feed and water. The lighting was provided for 24 h from day 0 to 4 and 23 h from day 5 to 21. The starting room temperature of 30°C was set 48 h prior to bird placement. The room temperature was then decreased to 27°C on day 7 and to 23°C on day 14. The birds’ circumstances and environment of the housing were monitored daily. There was no replacement of birds during the experiments. These studies were conducted in accordance with an approved animal use protocol from the Institutional Animal Care and Use Committee at Texas A&M University. Table 1. Experimental Diets and Nutrient Composition. Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 151.2% crude protein. 216.4% calcium and 21.3% phosphorus. 3Trace mineral premix added at this rate yields 149.6 mg manganese, 55.0 mg zinc, 26.4 mg iron, 4.4 mg copper, 1.05 mg iodine, 0.25 mg selenium, a minimum of 6.27 mg calcium, and a maximum of 8.69 mg calcium per kg of diet. The carrier is calcium carbonate, and the premix contains less than 1% mineral oil. 4Vitamin premix added at this rate yields 11,023 IU vitamin A, 3858 IU vitamin D3, 46 IU vitamin E, 0.0165 mg B12, 5.845 mg riboflavin, 45.93 mg niacin, 20.21 mg d-pantothenic acid, 477.67 mg choline, 1.47 mg menadione, 1.75 mg folic acid, 7.17 mg peroxidase, 2.94 mg thiamine, 0.55 mg biotin per kg diet. The carrier is ground rice hulls. View Large Table 1. Experimental Diets and Nutrient Composition. Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 151.2% crude protein. 216.4% calcium and 21.3% phosphorus. 3Trace mineral premix added at this rate yields 149.6 mg manganese, 55.0 mg zinc, 26.4 mg iron, 4.4 mg copper, 1.05 mg iodine, 0.25 mg selenium, a minimum of 6.27 mg calcium, and a maximum of 8.69 mg calcium per kg of diet. The carrier is calcium carbonate, and the premix contains less than 1% mineral oil. 4Vitamin premix added at this rate yields 11,023 IU vitamin A, 3858 IU vitamin D3, 46 IU vitamin E, 0.0165 mg B12, 5.845 mg riboflavin, 45.93 mg niacin, 20.21 mg d-pantothenic acid, 477.67 mg choline, 1.47 mg menadione, 1.75 mg folic acid, 7.17 mg peroxidase, 2.94 mg thiamine, 0.55 mg biotin per kg diet. The carrier is ground rice hulls. View Large Growth Performance The body weights (BWs) were recorded at day 1, 7, 14, and 21. The feed consumption (FC) was recorded at day 7, 14, and 21. Productivity index (PI) was calculated by following the formula: \begin{eqnarray*} {\rm{PI\ }} &=& \left( {100 - {\rm{Mortality}}} \right){\rm{\ }}\nonumber\\ &&\times \,{\rm{\ }}\left( {\frac{{{\rm{BW}}}}{{1000}}} \right)/{\rm{Bird\ Age}}/{\rm{FCR\ }} \times {\rm{\ }}100 \end{eqnarray*} Sample Collection At day 21, 4 randomly chosen birds from each battery unit were euthanized via CO2 asphyxiation to collect jejunum and ileum samples. Total length of the jejunum and ileum were measured from the first liver portal vein to Meckel's diverticulum and from Meckel's diverticulum to the cecal junction, respectively. The jejunum and ileum with digesta weights were also recorded to evaluate organ weights and indices. Distal sections of the jejunum and ileum samples were collected from 1 bird for histology. Digesta from whole sections of the jejunum and ileum were collected for viscosity from 1 bird. Whole sections of the ileal digesta from 2 birds were collected to analyze amino acid digestibility. Viscosity The samples were evaluated as described by Lee et al. [5]. Digesta from the jejunum and ileum were collected by gentle squeeze. Then, the digesta samples were centrifuged at 4,500 × g for 20 min. The supernatants were aliquoted and stored at –20°C until used. The samples were placed in a viscometer [13] and measured at 37.8°C. Centipoise (cP) readings were taken after measuring for 20 s at 5 rpm. Histology The jejunum and ileum samples were rinsed with phosphate-buffered saline 3 times and stored in 70% alcohol [14] for 24 h. Then, the samples were transferred into 10% buffered formalin [15] until fixed. The samples were transferred into 2 × 2 cassettes [16] with 10% buffered formalin. All samples were stained with Alcian Blue pH 2.5 at the Texas A&M University Histopathology/Immunopathology Laboratory. The stained sections were scanned by using the NanoZoomer 2.0-HT Digital slide scanner [17] at the Gastrointestinal Laboratory Department of Small Animal Clinical Sciences at Texas A&M University in order to measure villi height, width, crypt depth, and size and number of goblet cells of the jejunum and ileum using the NDP.view2 Viewing Software [18]. Digestibility An indigestible marker, 5 g/kg of titanium (IV) oxide [19] was added to the grower diet to analyze amino acid digestibility. The collected digesta samples were rinsed with distilled water, and then were freeze-dried [20]. The samples were analyzed by the Agricultural Experiment Station Chemical Laboratories at the University of Missouri-Columbia. The amino acid digestibility (AAD) coefficients were analyzed as described by Iyayi and Adeola [21]. The ADD was calculated by the following formula: \begin{eqnarray*} {\rm{AAD\ }} &=& \left\{ 1 - \Bigg( \frac{{{\rm{Titanium\ }}\left( {{\rm{IV}}} \right){\rm{Oxide\ }}\left( {{\rm{diet}}} \right)}}{{\rm{Titanium\ }}\left( {{\rm{IV}}} \right) {\rm{Oxide\ }}\left( {{\rm{ileal}}} \right)} \right.\nonumber\\ &&\left.\times \,\frac{{{\rm{Amino\ Acid\ }}\left( {{\rm{ileal}}} \right)}}{{{\rm{Amino\ Acid\ }}\left( {{\rm{diet}}} \right)}} \Bigg) \right\}\ \times \ 100 \end{eqnarray*} Body and Bone Composition Analysis A total of 40 birds (1 bird per unit) was euthanized via CO2 asphyxiation at day 24 and immediately transferred to the Applied Exercise Science Laboratory at Texas A&M University for dual-energy X-ray absorptiometry scanning to evaluate bone mineral density (BMD) and contents (BMC) as well as amounts of lean and fat tissues in the duck bodies. To determine their body and bone compositions, for each scan, 5 to 6 randomly selected ducks (whole carcass) were scanned twice, dorsal side up. In addition, both left and right tibiae were harvested to determine bone composition and strength. The bone length and weight were determined after bones were defatted with petroleum ether [22]. The left tibiae were used to determine bone ash. The dried bones were ashed at 600°C for 16 h [23]. Right tibiae were used to determine bone strength. The bones were sheared midshaft using a crosshead speed of 5.0 mm/min [24]. Statistical Analysis Data were analyzed using the standard least squares procedure by JMP Pro 12.0.1 for Windows [25]. Data from both experiments were analyzed with main effects of experiment (A and B), treatment (0%, 0.01%, 0.05%, 0.1%, and 0.2% β-mannanase), and room. The initial model included the 2-way interactions of the main effects. Room by treatment interactions were not significant and so were deleted from the final analyses. The final model included main effects of experiment and treatment and the interaction. The data means were separated using Student's t-test and deemed significantly different at P ≤ 0.05. A quadratic regression of β-mannanase levels on 21 d BW was performed. Figure 1. View largeDownload slide Quadratic regression of the dose of β-mannanase on the body weight of day 21 White Pekin duck. Figure 1. View largeDownload slide Quadratic regression of the dose of β-mannanase on the body weight of day 21 White Pekin duck. RESULTS AND DISCUSSION Growth Performances Table 2 presents results of the body weights (BW) and feed consumption (FC). All β-mannanase treated groups had significantly greater BW compared to control at day 14 (P < 0.0001) and at day 21 (P = 0.0007), respectively. Treatments 0.01% and 0.10% had significantly greater 14 d BW than 0.05%. No significant differences were observed in FC. The quadratic regression of dose effect of β-mannanase on the BW of 21-day-old ducklings is presented in Figure 1. The model estimated that the dose of β-mannanase resulting in maximum day 21 BW was 0.119%. Table 2. Effect of β-Mannanase on Body Weights per Bird (g) and Feed Consumption per Period per Bird (g) From day 1 to 21 in White Pekin Ducks. β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 2. Effect of β-Mannanase on Body Weights per Bird (g) and Feed Consumption per Period per Bird (g) From day 1 to 21 in White Pekin Ducks. β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 3 presents results of the feed conversion ratio (FCR) and productivity index (PI). All β-mannanase treated groups had significantly improved FCR compared to control at day 14 (P < 0.0001) and at day 21 (P = 0.0002), respectively. All β-mannanase treated groups had significantly better PI compared to control at day 7 (P = 0.0009), at day 14 (P < 0.0001), and at day 21 (P = 0.0003), respectively. Similar to the other results, a significant improvement in day 14 PI was observed between 0.01% and 0.10% compared to 0.05%. There were no significant dietary impacts on mortality (data not shown); thus, the improvement in PI is attributable to greater BW and improved FCR. Table 3. Effect of β-Mannanase on Feed Conversion Ratio and Productivity Index From Day 0 to 21 in White Pekin Ducks. β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 3. Effect of β-Mannanase on Feed Conversion Ratio and Productivity Index From Day 0 to 21 in White Pekin Ducks. β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large In this study, β-mannanase treated groups showed significantly better growth performance compared to control. These trends were also observed in several other studies that used β-mannanase in broiler chickens [26, 27]. Both chicken-based studies also observed that β-mannanase treated groups showed significantly improved growth performance. These results indicate that β-mannanase can improve growth performance significantly in White Pekin ducks. Viscosity and Histomorphological Development of the Jejunum and Ileum There were numerous instances of experiment × treatment interactions in evaluation of the histomorphological development of the jejunum and ileum. These interactions provided little if any useful information regarding the impacts of the treatments on these parameters and were more likely the result of low sample numbers and inherent variation within such measures. The subsequent discussion will thus include only those parameters in which no interactions were observed. There were no significant differences in the jejunum length (P = 0.4918), index (P = 0.7953), and viscosity (P = 0.4959), data not shown. All β-mannanase treated groups had significantly (P = 0.0051) longer ileum length compared to control (Table 4). Treatment 0.01% and 0.05% had significantly (P = 0.0433) lower ileal viscosity compared to control. No significant differences were observed among the groups in ileum index (P = 0.5901), data not shown. Mehri et al. [28] observed equivalent intestinal viscosity results where β-mannanase treated groups had statistically lower ileal viscosity than control group. These results demonstrate that β-mannanase affected the ileal intestinal morphology and viscosity of ducklings significantly. Table 4. Effect of β-Mannanase on Ileal Morphology, Viscosity, and Histomorphology in White Pekin Ducks. β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 4. Effect of β-Mannanase on Ileal Morphology, Viscosity, and Histomorphology in White Pekin Ducks. β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large There was no significant difference in jejunum crypt depth (P = 0.5382) and number of goblet cells (P = 0.1041), data not shown. Significant differences were observed in ileum crypt depth, villi height, and width (Table 4). Ducks fed 0.05%, 0.10%, and 0.20% β-mannanase had significantly (P < 0.0001) greater ileum crypt depth compared to control and 0.01% (Table 4). β-Mannanase at 0.10% had significantly (P = 0.0069) greater ileal villi height compared to control, 0.01%, and 0.20%. β-Mannanase levels of 0.05%, 0.10%, and 0.20% had significantly (P = 0.0095) greater ileum villi width compared to control. β-Mannanase had no significant effect on jejunum morphology development. However, β-mannanase did affect ileum morphology development. Especially, 0.10% β-mannanase showed significant impacts on ileum villi width, height, and crypt depth. The impacts of β-mannanase on intestinal morphology have also been observed in other studies utilizing broiler chickens. Saenphoom et al. [29] observed no differences in jejunum and ileum villi height and crypt depth of broiler chickens between mannanase treated and non-mannanase treated groups. The authors found significant differences only in duodenal crypt depth among the treatments. In another study, Mehri et al. [28] also observed similar histomorphology results with broiler chickens. The authors observed that β-mannanase treated groups had significantly greater jejunal villi height, crypt depth, and ileal crypt depth. A significant difference among dietary treatments was not observed (P = 0.1541) in ileum goblet cell size (Table 4). The 0.10% β-mannanase group had a significantly (P = 0.0006) greater number of ileum goblet cells compared to all other groups. β-Mannanase at 0.05% and 0.20% had also significantly greater numbers of ileum goblet cells compared to control, but there was no significant difference between control and 0.01%. β-Mannanase had no effect on ileum goblet cell size, but effected ileum goblet cell population. Therefore, the population of goblet cells is more responsive to the treatments than the size of goblet cells. Unlike our study, another study [28] observed contradictory results where the β-mannanase treated group had significantly lower populations of goblet cells than the control group in both jejunum and ileum in broiler chickens. In the present experiments, 0.10% β-mannanase had the highest population of goblet cells; this again indicates that 0.1% of β-mannanase is close to the most ideal β-mannanase level (0.119%) based on the BW at day 21 (Figure 1). Overall, β-mannanase in these experiments had significant impacts on ileum morphology and viscosity, but not on jejunum morphology and viscosity. The histomorphological results are consistent with growth performance. In conclusion, 0.1% of β-mannanase appears to be the ideal level to induce optimal intestinal morphology and viscosity. Digestibility All β-mannanase treated groups had significantly greater ileal Thr (P < 0.0001), Gly (P < 0.0001), Cys (P < 0.0001), Val (P < 0.0001), Met (P < 0.0001), Ile (P < 0.0001), Leu (P < 0.0001), Phe (P < 0.0001), Lys (P < 0.0001), His (P < 0.0001), and Arg (P < 0.0001) digestibility compared to control (Table 5). These results are similar to those of Mussini et al. [8] that used 0%, 0.025%, 0.05%, and 0.1% of β-mannanase in broiler chicken diets. The authors reported that β-mannanase treated groups had significantly greater ileal amino acid digestibility compared to the control group. The authors also observed that ileal amino acid digestibility was significantly increased with increasing β-mannanase concentration. However, there were no significant differences among the β-mannanase treated groups in our study, except in Trp digestibility. Treatment 0.10% had significantly greater (P < 0.0001) ileal Trp digestibility compared to control and 0.20% (Table 5). Table 5. Effect of Different Levels of β-Mannanase on Ileal Amino Acid Digestibility Coefficients (%) in White Pekin Ducks. β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 5. Effect of Different Levels of β-Mannanase on Ileal Amino Acid Digestibility Coefficients (%) in White Pekin Ducks. β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large His and Thr play important roles in mucin secretion. Lake et al. [30] reported that goblet cell mucin secretion function was stimulated by discharge of histamine from immunoglobulin E mediated mast cell. Threonine has functions that impact the synthesis of the mucin protein and protein phosphorylation and O-linked glycosylation in the intestine [31]. Horn et al. [32] performed a threonine deficiency experiment on White Pekin ducks and reported a correlation between mucin secretion and threonine. The authors reported that mucin secretion was increased by increasing the threonine concentration in duck diets. Goblet cell density and expression of mucin gene (MUC2) mRNA abundance were also increased as threonine increased. However, the authors did not find a correlation between threonine deficiency and mucin secretion in broiler chickens. Trp and Cys are also counted as important materials that are required for mucin backbone formation and synthesizing mucin protein, respectively [32]. In our amino acid digestibility results, all β-mannanase treated groups had greater ileal His, Thr, and Cys digestibility than control. Treatment 0.10% had significant improvement in Trp digestibility compared to control and 0.20%. Therefore, since 0.10% had the largest number of ileal goblet cells these results indicate that there is a relationship between amino acid digestibility (specifically threonine) and goblet cell population in ducks. In conclusion, although mucin layer thickness was not evaluated in this experiment, our histomorphology results showed that 0.10% had significantly greater ileal goblet cell population compared to all other groups. Our overall histomorphology results showed that 0.10% had the highest intestinal integrity small intestine. Body and Bone Composition No significant differences were observed in BMD (P = 0.5096), BMC (P = 0.9454), bone ash (P = 0.0674), bone length (P = 0.8973), bone weight (P = 0.3017), and the amount of lean tissue (P = 0.2565), data not shown. Salas et al. [33] reported that whole body DEXA scanning provided results highly correlated with actual body composition. β-Mannanase at 0.05% had significantly (P = 0.0331) greater bone strength compared to control and 0.20% (Table 6). β-Mannanase at 0.10% had significantly (P = 0.0189) lower fat tissue compared to control and 0.20% (Table 6). These results indicated that β-mannanase impacted the bone strength and the percentage of body fat of the ducklings. Table 6. Effect of β-Mannanase on Bone and Body Composition in White Pekin Ducks. β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 1Dietary level of β-mannanase, 800,000 U/kg. a,bMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 6. Effect of β-Mannanase on Bone and Body Composition in White Pekin Ducks. β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 1Dietary level of β-mannanase, 800,000 U/kg. a,bMeans within a column with different superscripts differ (P ≤ 0.05). View Large These results are consistent with the result of significantly increased amino acid digestibility. For example, Gly can be an important factor for uric acid synthesizing to achieve maximum growth of birds [34, 35]. Gly also forms chelates with metals [36]. Therefore, Gly not only maintains a healthy intestine, but also helps to absorb minerals. In conclusion, β-mannanase improves body and bone composition of White Pekin ducks. CONCLUSIONS AND APPLICATIONS The addition of β-mannanase (0.01%–0.20%, 800,000 U/kg) in duck diets resulted in increased 14 d BW by as much as 78 g (0.01%) and 21 d BW by as much as 106 g (0.10%). Feed conversion through 14 d was improved by 0.15 (0.01% and 0.20%) and through 21 d by 0.09 (0.01%). Productivity index was improved by the addition of β-mannanase by 45.2 at 7 d (0.01%), 88.2 at 14 d (0.02%), and 54.5 at 21 d (0.10%). Addition of β-mannanase resulted in a 4 cm increase ileal length (0.01% and 0.10%), a 0.74 cP reduction in viscosity of ileal digesta (0.05%), 16.7 μm greater crypt depth (0.10%), 64.5 μm greater villi height (0.10%), 25.9 μm greater villi width (0.05%), and a 44.5 more goblet cells (0.10%). Amino acid digestibility was improved (∼23%) by the addition of β-mannanase supplementation. Fat tissue in whole body (1.75%) and bone strength (4.54 kg) positively impact by the addition of β-mannanase supplementation. This study suggests that the 0.10% of β-mannanase is the most ideal level for the ducklings to derive better nutrient absorption and amino acid digestibility. Footnotes Primary Audience: Nutritionists, Live production personnel, Duck producers, Enzyme producers REFERENCES AND NOTES 1. Klein J. , Williams M. , Brown B. , Rao S. , Lee J. . 2015 . Effects of dietary inclusion of a cocktail NSPase and β-mannanase separately and in combination in low energy diets on broiler performance and processing parameters . J. Appl. Poult. 24 : 1 – 13 . Google Scholar CrossRef Search ADS 2. Liepman H. , Nairn C. , Willats W. , Sorensen I. , Roberts A. , Keegstra K. . 2007 . Functional genomic analysis supports conservation of function among cellulose synthase-like a gene family members and suggests diverse roles of mannans in plants . Plant Physiol. 143 : 1881 – 1893 . 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Corzo A. , Kidd M. , Dozier W. III , Kerr B. . 2009 . Dietary glycine and threonine interactive effects in broilers . J. Appl. Poult. Res. 18 : 79 – 84 . Google Scholar CrossRef Search ADS 36. Ashmead H. D. 1993 . The Roles of Amino Acid Chelates in Animal Nutrition . Noyes Publications , Park Ridge, NJ, USA . Acknowledgments This research was supported by funding from CTCBio Inc., Seoul, Korea. The authors also thank Maple Leaf Farms Inc., Leesburg, IN, United States, for their support. © 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 Journal of Applied Poultry Research Oxford University Press

Effects of a Commercial Beta-Mannanase Product on Growth Performance, Intestinal Histomorphology, Bone and Body Composition, and Amino Acid Digestibility in White Pekin Ducks

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Applied Poultry Science, Inc.
Copyright
© 2018 Poultry Science Association Inc.
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1056-6171
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1537-0437
D.O.I.
10.3382/japr/pfy016
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Abstract

Abstract Two experiments were conducted to evaluate effects of a commercial β-mannanase in duck diets 1–21 d. Both experiments included 0%, 0.01%, 0.05%, 0.1%, and 0.2% of β-mannanase treatments. Experimental units of 5 birds per pen were replicated 8 times in 4 different rooms. The data were analyzed as a 2 (Experiment) × 5 (Treatment) × 8 (Replicate) factorial analysis. Body weight of all β-mannanase groups was ∼66 g and ∼79 g greater than control fed birds at day 14 and 21, respectively. All β-mannanase groups had an average of 0.1, 0.14, and 0.08 lower feed conversion than controls at day 7, 14, and 21, respectively. Productivity index increased over controls by an average of 41, 81, and 48 on day 7, 14, and 21, respectively. Illeal length of all β-mannanase groups was greater than controls, and the 0.01% and 0.05% β-mannanase groups had ∼0.66 lower ileal viscosity than controls. Ducks fed 0.10% β-mannanase had greater ileal villi height than control, 0.01%, and 0.20% β-mannanase groups. Feeding diets with 0.05%, 0.10%, and 0.20% β-mannanase resulted in greater ileal villi width compared to controls. These treatments had greater ileal crypt depth than control and 0.05% β-mannanase groups. All β-mannanase treated groups had greater amino acid digestibility than controls. β-Mannanase at 0.10% resulted in a lower percentage of fat and greater bone strength than control and 0.20% β-mannanase. This study demonstrated that addition of β-mannanase positively affects duck growth performance, gut morphology, and digestibility. DESCRIPTION OF THE PROBLEM As the use of antibiotics is prohibited in the poultry industry, researchers have specifically focused on the development of innovative alternatives to antibiotic additives in poultry diets to improve growth performance and reduce mortality. Monogastric animals, such as poultry, are not able to completely digest non-starch polysaccharides (NSPs); hence, they often require enzymes to break down β (α)-linked NSPs [1]. Corn and soybean meal are the most common main ingredients for poultry diets that contain β-mannan, which is one kind of NSPs. β-Mannan is composed of multiple mannose and glucose units in β-1,4-linkages as the backbone [2], and may also be linked to galactose residues by α-1,6-linkage [3]. β-Mannan is known to increase intestinal viscosity. The increase of intestinal viscosity can lead to reduced nutrient absorption [4] and rate of nutrient passage [5], and also impact intestinal morphology [6]. β-Mannanase inhibits the negative effects of NSPs in poultry by directly degrading the NSPs in the plant cell walls [7]. β-Mannanase is an endo-type enzyme and assists in breaking the β-mannan backbone chains. Therefore, if birds ingest the β-mannanase, it increases their growth performance by cleaving the NSPs links, which then improves nutrient digestibility. Effects of β-mannanase have already been examined through research with chickens. Mussini et al. [8] used a commercial β-mannanase product in broiler chicken diets. These authors reported that the groups treated with β-mannanase showed significantly better amino acid digestibility compared to the controls. Ayoola et al. [9] evaluated the effects of β-mannanase on enteric mucosal morphological development and adherent mucus layer thickness in turkeys. This study found that β-mannanase impacted villi morphology, surface area, and mucin thickness. Even though β-mannanase is one of the most widely used enzymes for poultry, research with β-mannanase in ducks is limited. Therefore, this study was conducted to determine the effects of β-mannanase on White Pekin ducks. Our study used 5 different concentrations of β-mannanase to determine the effects on growth performance, intestinal morphology, bone and body composition, and amino acid digestibility in Pekin ducks. MATERIALS AND METHODS Experimental Design Two identical experiments (A and B) were conducted. In each experiment, a total of 200 mixed-sex day-old ducklings were randomly housed in 40 pens with 5 birds per pen. Pens were assigned to 5 dietary treatments and arranged as 8 replicates (2 each in 4 rooms) resulting in a total of 40 ducks per dietary treatment. Birds, Housing, and Diets White Pekin duck eggs were obtained from a commercial source [10]. The eggs were incubated and hatched, and healthy ducklings were selected at the Texas A&M University Poultry Research, Teaching and Extension Center (TAMUPRC). The dietary treatments were 0.0%, 0.01%, 0.05%, 0.10%, and 0.20% commercial β-mannanase (800,000 U/kg) [11]. The diet formulations were adapted from Zeng et al. [12] with minor modifications (Table 1). In both experiments, starter (day 0–13) and grower (day 14–21) diets were mixed and pelleted at the TAMUPRC feed mill. Pen dimensions were 0.97 × 0.67 × 0.24 m, which allowed 0.03 m3/bird at placement. Each pen consisted of 1 feeder and 1 water tray and an ad libitum supply of feed and water. The lighting was provided for 24 h from day 0 to 4 and 23 h from day 5 to 21. The starting room temperature of 30°C was set 48 h prior to bird placement. The room temperature was then decreased to 27°C on day 7 and to 23°C on day 14. The birds’ circumstances and environment of the housing were monitored daily. There was no replacement of birds during the experiments. These studies were conducted in accordance with an approved animal use protocol from the Institutional Animal Care and Use Committee at Texas A&M University. Table 1. Experimental Diets and Nutrient Composition. Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 151.2% crude protein. 216.4% calcium and 21.3% phosphorus. 3Trace mineral premix added at this rate yields 149.6 mg manganese, 55.0 mg zinc, 26.4 mg iron, 4.4 mg copper, 1.05 mg iodine, 0.25 mg selenium, a minimum of 6.27 mg calcium, and a maximum of 8.69 mg calcium per kg of diet. The carrier is calcium carbonate, and the premix contains less than 1% mineral oil. 4Vitamin premix added at this rate yields 11,023 IU vitamin A, 3858 IU vitamin D3, 46 IU vitamin E, 0.0165 mg B12, 5.845 mg riboflavin, 45.93 mg niacin, 20.21 mg d-pantothenic acid, 477.67 mg choline, 1.47 mg menadione, 1.75 mg folic acid, 7.17 mg peroxidase, 2.94 mg thiamine, 0.55 mg biotin per kg diet. The carrier is ground rice hulls. View Large Table 1. Experimental Diets and Nutrient Composition. Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 Starter Grower 1–13 d 14–21 d Ingredients (%)  Corn, yellow grain 42.00 53.70  Soybean meal, dehulled solvent1 39.89 27.63  Wheat bran 6.00 6.00  DL Methionine 0.35 0.26  L-lysine 0.07 0.07  Fat, blended A/V 6.74 8.78  Limestone 2.64 1.16  Monocalcium phosphate2 1.27 1.35  Salt 0.44 0.44  Trace mineral3 0.05 0.05  Vitamins4 0.25 0.25 Calculated nutrient composition  Crude protein, % 24.00 19.00  ME, kcal/kg 3038 3298  Crude fat, % 8.88 11.22  Lysine, % 1.38 1.04  Methionine, % 0.70 0.55  Cysteine, % 0.38 0.32  Tryptophan, % 0.30 0.23  Threonine, % 0.90 0.71  Arginine, % 1.64 1.25  Valine, % 1.10 0.87  Calcium, % 1.33 0.75  Phosphorus, % 0.70 0.68  Sodium, % 0.19 0.19 Analyzed composition  Crude protein, % 22.88 19.07  Lysine, % 1.08  Methionine, % 0.48 151.2% crude protein. 216.4% calcium and 21.3% phosphorus. 3Trace mineral premix added at this rate yields 149.6 mg manganese, 55.0 mg zinc, 26.4 mg iron, 4.4 mg copper, 1.05 mg iodine, 0.25 mg selenium, a minimum of 6.27 mg calcium, and a maximum of 8.69 mg calcium per kg of diet. The carrier is calcium carbonate, and the premix contains less than 1% mineral oil. 4Vitamin premix added at this rate yields 11,023 IU vitamin A, 3858 IU vitamin D3, 46 IU vitamin E, 0.0165 mg B12, 5.845 mg riboflavin, 45.93 mg niacin, 20.21 mg d-pantothenic acid, 477.67 mg choline, 1.47 mg menadione, 1.75 mg folic acid, 7.17 mg peroxidase, 2.94 mg thiamine, 0.55 mg biotin per kg diet. The carrier is ground rice hulls. View Large Growth Performance The body weights (BWs) were recorded at day 1, 7, 14, and 21. The feed consumption (FC) was recorded at day 7, 14, and 21. Productivity index (PI) was calculated by following the formula: \begin{eqnarray*} {\rm{PI\ }} &=& \left( {100 - {\rm{Mortality}}} \right){\rm{\ }}\nonumber\\ &&\times \,{\rm{\ }}\left( {\frac{{{\rm{BW}}}}{{1000}}} \right)/{\rm{Bird\ Age}}/{\rm{FCR\ }} \times {\rm{\ }}100 \end{eqnarray*} Sample Collection At day 21, 4 randomly chosen birds from each battery unit were euthanized via CO2 asphyxiation to collect jejunum and ileum samples. Total length of the jejunum and ileum were measured from the first liver portal vein to Meckel's diverticulum and from Meckel's diverticulum to the cecal junction, respectively. The jejunum and ileum with digesta weights were also recorded to evaluate organ weights and indices. Distal sections of the jejunum and ileum samples were collected from 1 bird for histology. Digesta from whole sections of the jejunum and ileum were collected for viscosity from 1 bird. Whole sections of the ileal digesta from 2 birds were collected to analyze amino acid digestibility. Viscosity The samples were evaluated as described by Lee et al. [5]. Digesta from the jejunum and ileum were collected by gentle squeeze. Then, the digesta samples were centrifuged at 4,500 × g for 20 min. The supernatants were aliquoted and stored at –20°C until used. The samples were placed in a viscometer [13] and measured at 37.8°C. Centipoise (cP) readings were taken after measuring for 20 s at 5 rpm. Histology The jejunum and ileum samples were rinsed with phosphate-buffered saline 3 times and stored in 70% alcohol [14] for 24 h. Then, the samples were transferred into 10% buffered formalin [15] until fixed. The samples were transferred into 2 × 2 cassettes [16] with 10% buffered formalin. All samples were stained with Alcian Blue pH 2.5 at the Texas A&M University Histopathology/Immunopathology Laboratory. The stained sections were scanned by using the NanoZoomer 2.0-HT Digital slide scanner [17] at the Gastrointestinal Laboratory Department of Small Animal Clinical Sciences at Texas A&M University in order to measure villi height, width, crypt depth, and size and number of goblet cells of the jejunum and ileum using the NDP.view2 Viewing Software [18]. Digestibility An indigestible marker, 5 g/kg of titanium (IV) oxide [19] was added to the grower diet to analyze amino acid digestibility. The collected digesta samples were rinsed with distilled water, and then were freeze-dried [20]. The samples were analyzed by the Agricultural Experiment Station Chemical Laboratories at the University of Missouri-Columbia. The amino acid digestibility (AAD) coefficients were analyzed as described by Iyayi and Adeola [21]. The ADD was calculated by the following formula: \begin{eqnarray*} {\rm{AAD\ }} &=& \left\{ 1 - \Bigg( \frac{{{\rm{Titanium\ }}\left( {{\rm{IV}}} \right){\rm{Oxide\ }}\left( {{\rm{diet}}} \right)}}{{\rm{Titanium\ }}\left( {{\rm{IV}}} \right) {\rm{Oxide\ }}\left( {{\rm{ileal}}} \right)} \right.\nonumber\\ &&\left.\times \,\frac{{{\rm{Amino\ Acid\ }}\left( {{\rm{ileal}}} \right)}}{{{\rm{Amino\ Acid\ }}\left( {{\rm{diet}}} \right)}} \Bigg) \right\}\ \times \ 100 \end{eqnarray*} Body and Bone Composition Analysis A total of 40 birds (1 bird per unit) was euthanized via CO2 asphyxiation at day 24 and immediately transferred to the Applied Exercise Science Laboratory at Texas A&M University for dual-energy X-ray absorptiometry scanning to evaluate bone mineral density (BMD) and contents (BMC) as well as amounts of lean and fat tissues in the duck bodies. To determine their body and bone compositions, for each scan, 5 to 6 randomly selected ducks (whole carcass) were scanned twice, dorsal side up. In addition, both left and right tibiae were harvested to determine bone composition and strength. The bone length and weight were determined after bones were defatted with petroleum ether [22]. The left tibiae were used to determine bone ash. The dried bones were ashed at 600°C for 16 h [23]. Right tibiae were used to determine bone strength. The bones were sheared midshaft using a crosshead speed of 5.0 mm/min [24]. Statistical Analysis Data were analyzed using the standard least squares procedure by JMP Pro 12.0.1 for Windows [25]. Data from both experiments were analyzed with main effects of experiment (A and B), treatment (0%, 0.01%, 0.05%, 0.1%, and 0.2% β-mannanase), and room. The initial model included the 2-way interactions of the main effects. Room by treatment interactions were not significant and so were deleted from the final analyses. The final model included main effects of experiment and treatment and the interaction. The data means were separated using Student's t-test and deemed significantly different at P ≤ 0.05. A quadratic regression of β-mannanase levels on 21 d BW was performed. Figure 1. View largeDownload slide Quadratic regression of the dose of β-mannanase on the body weight of day 21 White Pekin duck. Figure 1. View largeDownload slide Quadratic regression of the dose of β-mannanase on the body weight of day 21 White Pekin duck. RESULTS AND DISCUSSION Growth Performances Table 2 presents results of the body weights (BW) and feed consumption (FC). All β-mannanase treated groups had significantly greater BW compared to control at day 14 (P < 0.0001) and at day 21 (P = 0.0007), respectively. Treatments 0.01% and 0.10% had significantly greater 14 d BW than 0.05%. No significant differences were observed in FC. The quadratic regression of dose effect of β-mannanase on the BW of 21-day-old ducklings is presented in Figure 1. The model estimated that the dose of β-mannanase resulting in maximum day 21 BW was 0.119%. Table 2. Effect of β-Mannanase on Body Weights per Bird (g) and Feed Consumption per Period per Bird (g) From day 1 to 21 in White Pekin Ducks. β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 2. Effect of β-Mannanase on Body Weights per Bird (g) and Feed Consumption per Period per Bird (g) From day 1 to 21 in White Pekin Ducks. β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 β-Mannanase1 (%) Body weight (g) Feed consumption (g) d1 d7 d14 d21 d7 d14 d21 0.00 57 208 649c 1262b 177 568 925 0.01 57 225 727a 1334a 180 561 935 0.05 57 222 691b 1329a 179 549 930 0.10 58 226 722a 1368a 184 565 952 0.20 57 221 719a,b 1331a 180 561 969 Pooled SEM 4.89 11.55 17.76 4.60 9.64 15.26 Treatment N/A 0.0597 <0.0001 0.0007 0.7537 0.7668 0.2181 Experiment 0.0027 0.2628 0.0002 0.1466 0.7490 <0.0001 Treatment × Experiment 0.7215 0.5842 0.1944 0.6346 0.3524 0.4974 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 3 presents results of the feed conversion ratio (FCR) and productivity index (PI). All β-mannanase treated groups had significantly improved FCR compared to control at day 14 (P < 0.0001) and at day 21 (P = 0.0002), respectively. All β-mannanase treated groups had significantly better PI compared to control at day 7 (P = 0.0009), at day 14 (P < 0.0001), and at day 21 (P = 0.0003), respectively. Similar to the other results, a significant improvement in day 14 PI was observed between 0.01% and 0.10% compared to 0.05%. There were no significant dietary impacts on mortality (data not shown); thus, the improvement in PI is attributable to greater BW and improved FCR. Table 3. Effect of β-Mannanase on Feed Conversion Ratio and Productivity Index From Day 0 to 21 in White Pekin Ducks. β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 3. Effect of β-Mannanase on Feed Conversion Ratio and Productivity Index From Day 0 to 21 in White Pekin Ducks. β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 β-Mannanase1 (%) Feed conversion ratio Productivity index d0 to 7 d0 to 14 d0 to 21 d7 d14 d21 0.00 1.20b 1.27b 1.40b 253.8b 370.7c 434.6b 0.01 1.09a 1.12a 1.31a 299.0a 458.2a 484.4a 0.05 1.10a 1.16a 1.32a 291.7a 432.1b 479.1a 0.10 1.11a 1.13a 1.32a 296.1a 456.7a 489.1a 0.20 1.11a 1.12a 1.33a 289.1a 458.9a 476.5a Pooled SEM 0.01 0.02 0.01 8.34 10.98 9.47 Treatment <0.0001 <0.0001 0.0002 0.0009 <0.0001 0.0003 Experiment <0.0001 0.1819 0.2290 <0.0001 0.0513 0.1761 Treatment × Experiment 0.7867 0.9305 0.5164 0.7370 0.6109 0.2016 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large In this study, β-mannanase treated groups showed significantly better growth performance compared to control. These trends were also observed in several other studies that used β-mannanase in broiler chickens [26, 27]. Both chicken-based studies also observed that β-mannanase treated groups showed significantly improved growth performance. These results indicate that β-mannanase can improve growth performance significantly in White Pekin ducks. Viscosity and Histomorphological Development of the Jejunum and Ileum There were numerous instances of experiment × treatment interactions in evaluation of the histomorphological development of the jejunum and ileum. These interactions provided little if any useful information regarding the impacts of the treatments on these parameters and were more likely the result of low sample numbers and inherent variation within such measures. The subsequent discussion will thus include only those parameters in which no interactions were observed. There were no significant differences in the jejunum length (P = 0.4918), index (P = 0.7953), and viscosity (P = 0.4959), data not shown. All β-mannanase treated groups had significantly (P = 0.0051) longer ileum length compared to control (Table 4). Treatment 0.01% and 0.05% had significantly (P = 0.0433) lower ileal viscosity compared to control. No significant differences were observed among the groups in ileum index (P = 0.5901), data not shown. Mehri et al. [28] observed equivalent intestinal viscosity results where β-mannanase treated groups had statistically lower ileal viscosity than control group. These results demonstrate that β-mannanase affected the ileal intestinal morphology and viscosity of ducklings significantly. Table 4. Effect of β-Mannanase on Ileal Morphology, Viscosity, and Histomorphology in White Pekin Ducks. β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 4. Effect of β-Mannanase on Ileal Morphology, Viscosity, and Histomorphology in White Pekin Ducks. β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 β-Mannanase1 Length Viscosity Crypt depth Villi height Villi width Goblet cell Goblet cell (%) (cm) (cP) (μm) (μm) (μm) area (μm2) numbers (#) 0.00 65b 3.05a 144.9b 652.7b 175.8b 23.2 85.9c 0.01 69a 2.47b 149.6b 668.0b 186.3a,b 21.0 104.8b,c 0.05 68a 2.31b 158.1a 674.0a,b 201.7a 19.4 108.3b 0.10 69a 2.69a,b 161.5a 717.2a 198.1a 24.7 130.4a 0.20 67a 2.64a,b 157.4a 644.4b 193.3a 22.6 108.7b Pooled SEM 0.91 0.17 3.85 13.26 6.02 1.36 8.63 Treatment 0.0051 0.0433 <0.0001 0.0069 0.0095 0.1541 0.0006 Experiment 0.0741 <0.0001 0.0648 <0.0001 0.7372 0.0003 0.0020 Treatment × Experiment 0.3322 0.7491 0.1522 0.0578 0.2257 0.1652 0.3552 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large There was no significant difference in jejunum crypt depth (P = 0.5382) and number of goblet cells (P = 0.1041), data not shown. Significant differences were observed in ileum crypt depth, villi height, and width (Table 4). Ducks fed 0.05%, 0.10%, and 0.20% β-mannanase had significantly (P < 0.0001) greater ileum crypt depth compared to control and 0.01% (Table 4). β-Mannanase at 0.10% had significantly (P = 0.0069) greater ileal villi height compared to control, 0.01%, and 0.20%. β-Mannanase levels of 0.05%, 0.10%, and 0.20% had significantly (P = 0.0095) greater ileum villi width compared to control. β-Mannanase had no significant effect on jejunum morphology development. However, β-mannanase did affect ileum morphology development. Especially, 0.10% β-mannanase showed significant impacts on ileum villi width, height, and crypt depth. The impacts of β-mannanase on intestinal morphology have also been observed in other studies utilizing broiler chickens. Saenphoom et al. [29] observed no differences in jejunum and ileum villi height and crypt depth of broiler chickens between mannanase treated and non-mannanase treated groups. The authors found significant differences only in duodenal crypt depth among the treatments. In another study, Mehri et al. [28] also observed similar histomorphology results with broiler chickens. The authors observed that β-mannanase treated groups had significantly greater jejunal villi height, crypt depth, and ileal crypt depth. A significant difference among dietary treatments was not observed (P = 0.1541) in ileum goblet cell size (Table 4). The 0.10% β-mannanase group had a significantly (P = 0.0006) greater number of ileum goblet cells compared to all other groups. β-Mannanase at 0.05% and 0.20% had also significantly greater numbers of ileum goblet cells compared to control, but there was no significant difference between control and 0.01%. β-Mannanase had no effect on ileum goblet cell size, but effected ileum goblet cell population. Therefore, the population of goblet cells is more responsive to the treatments than the size of goblet cells. Unlike our study, another study [28] observed contradictory results where the β-mannanase treated group had significantly lower populations of goblet cells than the control group in both jejunum and ileum in broiler chickens. In the present experiments, 0.10% β-mannanase had the highest population of goblet cells; this again indicates that 0.1% of β-mannanase is close to the most ideal β-mannanase level (0.119%) based on the BW at day 21 (Figure 1). Overall, β-mannanase in these experiments had significant impacts on ileum morphology and viscosity, but not on jejunum morphology and viscosity. The histomorphological results are consistent with growth performance. In conclusion, 0.1% of β-mannanase appears to be the ideal level to induce optimal intestinal morphology and viscosity. Digestibility All β-mannanase treated groups had significantly greater ileal Thr (P < 0.0001), Gly (P < 0.0001), Cys (P < 0.0001), Val (P < 0.0001), Met (P < 0.0001), Ile (P < 0.0001), Leu (P < 0.0001), Phe (P < 0.0001), Lys (P < 0.0001), His (P < 0.0001), and Arg (P < 0.0001) digestibility compared to control (Table 5). These results are similar to those of Mussini et al. [8] that used 0%, 0.025%, 0.05%, and 0.1% of β-mannanase in broiler chicken diets. The authors reported that β-mannanase treated groups had significantly greater ileal amino acid digestibility compared to the control group. The authors also observed that ileal amino acid digestibility was significantly increased with increasing β-mannanase concentration. However, there were no significant differences among the β-mannanase treated groups in our study, except in Trp digestibility. Treatment 0.10% had significantly greater (P < 0.0001) ileal Trp digestibility compared to control and 0.20% (Table 5). Table 5. Effect of Different Levels of β-Mannanase on Ileal Amino Acid Digestibility Coefficients (%) in White Pekin Ducks. β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 5. Effect of Different Levels of β-Mannanase on Ileal Amino Acid Digestibility Coefficients (%) in White Pekin Ducks. β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 β-Mannanase1 (%) Thr Gly Cys Val Met Ile Leu Phe Lys His Arg Trp CON 49.26b 55.42b 45.41b 57.47b 80.59b 63.03b 66.06b 65.14b 63.48b 66.36b 73.27b 66.99c 0.00 71.56a 73.10a 69.59a 76.16a 87.90a 79.10a 80.44a 80.59a 78.16a 81.28a 84.59a 81.51a,b 0.01 72.27a 73.13a 71.42a 76.79a 90.15a 79.45a 80.82a 80.80a 79.18a 81.37a 85.16a 81.80a,b 0.05 75.26a 76.47a 74.01a 79.21a 89.87a 81.85a 82.91a 82.98a 81.14a 83.51a 86.36a 85.25a 0.10 72.46a 74.06a 71.26a 76.76a 88.15a 79.45a 80.65a 80.62a 78.20a 81.23a 84.37a 79.70b Pooled SEM 1.716 1.526 1.602 1.586 1.099 1.472 1.352 1.323 1.800 1.276 1.214 1.633 Treatment <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Experiment 0.2579 0.2559 0.0581 0.0600 0.2885 0.1809 0.0686 0.2810 0.6518 0.2202 0.2065 0.0008 Treatment × Experiment 0.2898 0.2204 0.8170 0.2094 0.3574 0.2727 0.3440 0.2239 0.2727 0.4247 0.3446 0.4868 1Dietary level of β-mannanase, 800,000 U/kg. a–cMeans within a column with different superscripts differ (P ≤ 0.05). View Large His and Thr play important roles in mucin secretion. Lake et al. [30] reported that goblet cell mucin secretion function was stimulated by discharge of histamine from immunoglobulin E mediated mast cell. Threonine has functions that impact the synthesis of the mucin protein and protein phosphorylation and O-linked glycosylation in the intestine [31]. Horn et al. [32] performed a threonine deficiency experiment on White Pekin ducks and reported a correlation between mucin secretion and threonine. The authors reported that mucin secretion was increased by increasing the threonine concentration in duck diets. Goblet cell density and expression of mucin gene (MUC2) mRNA abundance were also increased as threonine increased. However, the authors did not find a correlation between threonine deficiency and mucin secretion in broiler chickens. Trp and Cys are also counted as important materials that are required for mucin backbone formation and synthesizing mucin protein, respectively [32]. In our amino acid digestibility results, all β-mannanase treated groups had greater ileal His, Thr, and Cys digestibility than control. Treatment 0.10% had significant improvement in Trp digestibility compared to control and 0.20%. Therefore, since 0.10% had the largest number of ileal goblet cells these results indicate that there is a relationship between amino acid digestibility (specifically threonine) and goblet cell population in ducks. In conclusion, although mucin layer thickness was not evaluated in this experiment, our histomorphology results showed that 0.10% had significantly greater ileal goblet cell population compared to all other groups. Our overall histomorphology results showed that 0.10% had the highest intestinal integrity small intestine. Body and Bone Composition No significant differences were observed in BMD (P = 0.5096), BMC (P = 0.9454), bone ash (P = 0.0674), bone length (P = 0.8973), bone weight (P = 0.3017), and the amount of lean tissue (P = 0.2565), data not shown. Salas et al. [33] reported that whole body DEXA scanning provided results highly correlated with actual body composition. β-Mannanase at 0.05% had significantly (P = 0.0331) greater bone strength compared to control and 0.20% (Table 6). β-Mannanase at 0.10% had significantly (P = 0.0189) lower fat tissue compared to control and 0.20% (Table 6). These results indicated that β-mannanase impacted the bone strength and the percentage of body fat of the ducklings. Table 6. Effect of β-Mannanase on Bone and Body Composition in White Pekin Ducks. β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 1Dietary level of β-mannanase, 800,000 U/kg. a,bMeans within a column with different superscripts differ (P ≤ 0.05). View Large Table 6. Effect of β-Mannanase on Bone and Body Composition in White Pekin Ducks. β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 β-Mannanase1 Fat tissue Bone strength (%) (%) (kg) CON 12.87a 17.77b 0.00 11.72a,b 19.12a,b 0.01 11.53a,b 22.31a 0.05 11.12b 19.22a,b 0.10 12.29a 16.12b Pooled SEM 0.4332 1.3313 Treatment 0.0189 0.0331 Experiment 0.3071 <0.0001 Treatment × Experiment 0.0850 0.1381 1Dietary level of β-mannanase, 800,000 U/kg. a,bMeans within a column with different superscripts differ (P ≤ 0.05). View Large These results are consistent with the result of significantly increased amino acid digestibility. For example, Gly can be an important factor for uric acid synthesizing to achieve maximum growth of birds [34, 35]. Gly also forms chelates with metals [36]. Therefore, Gly not only maintains a healthy intestine, but also helps to absorb minerals. In conclusion, β-mannanase improves body and bone composition of White Pekin ducks. CONCLUSIONS AND APPLICATIONS The addition of β-mannanase (0.01%–0.20%, 800,000 U/kg) in duck diets resulted in increased 14 d BW by as much as 78 g (0.01%) and 21 d BW by as much as 106 g (0.10%). Feed conversion through 14 d was improved by 0.15 (0.01% and 0.20%) and through 21 d by 0.09 (0.01%). Productivity index was improved by the addition of β-mannanase by 45.2 at 7 d (0.01%), 88.2 at 14 d (0.02%), and 54.5 at 21 d (0.10%). Addition of β-mannanase resulted in a 4 cm increase ileal length (0.01% and 0.10%), a 0.74 cP reduction in viscosity of ileal digesta (0.05%), 16.7 μm greater crypt depth (0.10%), 64.5 μm greater villi height (0.10%), 25.9 μm greater villi width (0.05%), and a 44.5 more goblet cells (0.10%). Amino acid digestibility was improved (∼23%) by the addition of β-mannanase supplementation. Fat tissue in whole body (1.75%) and bone strength (4.54 kg) positively impact by the addition of β-mannanase supplementation. This study suggests that the 0.10% of β-mannanase is the most ideal level for the ducklings to derive better nutrient absorption and amino acid digestibility. Footnotes Primary Audience: Nutritionists, Live production personnel, Duck producers, Enzyme producers REFERENCES AND NOTES 1. Klein J. , Williams M. , Brown B. , Rao S. , Lee J. . 2015 . Effects of dietary inclusion of a cocktail NSPase and β-mannanase separately and in combination in low energy diets on broiler performance and processing parameters . J. Appl. Poult. 24 : 1 – 13 . Google Scholar CrossRef Search ADS 2. Liepman H. , Nairn C. , Willats W. , Sorensen I. , Roberts A. , Keegstra K. . 2007 . Functional genomic analysis supports conservation of function among cellulose synthase-like a gene family members and suggests diverse roles of mannans in plants . Plant Physiol. 143 : 1881 – 1893 . 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Corzo A. , Kidd M. , Dozier W. III , Kerr B. . 2009 . Dietary glycine and threonine interactive effects in broilers . J. Appl. Poult. Res. 18 : 79 – 84 . Google Scholar CrossRef Search ADS 36. Ashmead H. D. 1993 . The Roles of Amino Acid Chelates in Animal Nutrition . Noyes Publications , Park Ridge, NJ, USA . Acknowledgments This research was supported by funding from CTCBio Inc., Seoul, Korea. The authors also thank Maple Leaf Farms Inc., Leesburg, IN, United States, for their support. © 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)

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Journal of Applied Poultry ResearchOxford University Press

Published: May 14, 2018

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