Incidence, severity, and relationship of broiler footpad lesions and gait scores of market-age broilers raised under commercial conditions in the southeastern United States

Incidence, severity, and relationship of broiler footpad lesions and gait scores of market-age... SUMMARY The prevalence and severity of footpad dermatitis (FPD) and gait score (GS) as an indicator of lameness in commercial broiler production in the United States has not been widely reported. The objectives of this field study were to determine the prevalence and severity of FPD and lameness in commercial broilers, as well as the relationship between FPD and GS under the production conditions typical of the southeastern United States. Observations were collected from an integrated broiler complex producing a light broiler (1.94 to 2.22 kg) and an integrated broiler complex producing a heavier broiler (3.62 to 3.76 kg). Data were collected from 554 farms, 16,697 houses, and 166,977 broilers, representing over 328 million birds over the 3-year span of the study. Light broilers had significantly better FPD and GS than heavier broilers. Additionally, there was a strongly significant association between FPD and GS within a complex. There were significantly greater odds of GS worsening as FPD worsened and significantly high odds of FPD becoming more severe as GS worsened. DESCRIPTION OF PROBLEM In spite of tremendous advances in breeding, health, nutrition, and environmental control, footpad dermatitis (FPD) and lameness continue to be important welfare concerns facing the modern broiler industry [1–3]. Comprehensive information on the pathology and etiology of FPD [4–8] and lameness [9–11] in poultry has been published. Primary contributors to the development of FPD in poultry are the type of bedding material and high litter moisture. Gross FPD is usually categorized using a 3-point scale based on lesion severity [12, 13]. Lameness, on the other hand, has a more complex etiology involving both infectious and non-infectious causes [14]. Lameness has been scored kinetically by visually observing and categorizing the walking ability (i.e., gait) of broilers [15, 16]. A 3-point gait score (GS) system has been validated to assess overall leg health in commercial broiler flocks [17]. Although simple to implement and widely adapted to assess lameness, GS is subjective and not a very sensitive tool to discriminate if pain is involved with leg abnormalities and pathologies at the farm level [18, 19]. Reports from Europe indicate a high proportion of broilers with FPD and lameness [15, 20–22]. These studies are in contrast, however, to a recent study in which a steady improvement over time in leg health is reported in broilers [23]. The relationship between FPD and lameness as measured by GS is not clear. When present, abnormal gait was not associated with physiological stress or stress-associated pain [24, 25]. Reluctance to move was reported only in broilers exhibiting inflammatory FPD [26, 27]. Other studies could not demonstrate a correlation between FPD and GS under controlled experiments [28, 29]. The objectives of this field study were to determine the prevalence and severity of FPD and lameness in commercial broilers, as well as the relationship between FPD and GS under the production conditions typical of the southeastern United States—tunnel-ventilated, evaporative cooled, floor-raised broilers in which bedding material consists of at least 10 cm of pine shavings, peanut hulls, or some combination. While bedding is maintained at a depth of 10 cm, it is typically not totally removed after each flock; rather, the caked material is removed at the end of each flock, and new material is added back to maintain at least the 10 cm depth. MATERIALS AND METHODS Birds and Housing This study involved 2 commercial integrated broiler complexes in the southeastern United States from 2012 to 2014. One complex (A) produced a small broiler (1.94 to 2.22 kg), while the other (B) produced a heavier broiler (3.62 to 3.76 kg). A Hubbard M99 x Cobb 500 cross was used in complex A, and a Ross 344 x Ross 708 cross was used in complex B. Data were collected from 554 farms, 16,697 houses, and 166,977 broilers, representing over 328 million birds over the 3-year span of the study. Production volume and characteristics of each integrated complex for each yr are presented in Table 1. Table 1. Production characteristics. Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 View Large Table 1. Production characteristics. Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 View Large All commercial broiler houses assessed were of standard size (12 m x 152 m or larger), had power-assisted tunnel ventilation with 15 cm evaporative cooling pad systems, and were either curtain-sided, solid side-walled, or a combination of both. All houses had at least 4 lines of nipple drinkers and 2 feeder lines. Bedding material was allowed to build up and complete clean-out down to the dirt pad was done, on average, once per yr per house. If complete clean-out of a house was not completed, caked bedding material was removed from the house, and fresh bedding material was added back to attain at least 10 cm dry, un-caked litter base. Bedding material consisted of peanut hulls, pine shavings, or a combination of the 2 materials. Broilers received a standard 4-stage diet consisting of starter, grower, finisher, and withdrawal feeds. The general nutritional plan for each feed between complexes was similar with the major difference being the feed quantity of each specific feed type provided to the bird based on the age of processing within each complex. Generally speaking, both complexes provided approximately the same amount of starter feed, but complex B provided 2 to 3 times more grower, finisher, and withdrawal feeds per bird. Measures As part of their normal flock service visit and animal welfare verification checks [30], trained company flock service technicians examined 10 randomly selected broilers per house for FPD [31] and GS [32, 33] 7 to 10 d prior to processing. In order to assess the relationship between FPD and GS, each of the 10 birds per house was scored for both attributes, and the data for each bird were linked. Statistics The 1st ordinal logistic model was used to compare FPD and GS distribution by production complex. Distribution of FPD and GS was analyzed using the GLIMMIX procedure of SAS®, version 9.3 or later [34, 35]. The association between FPD and GS was analyzed using the FREQ procedure of SAS® [36]. The 2nd ordinal logistic model compared the distribution of FPD score for different levels of GS by complex. The 3rd ordinal logistic model compared the distribution of GS for different levels of FPD by complex. Both the 2nd and 3rd ordinal logistic models were analyzed using the GENMOD procedure of SAS® [37]. RESULTS AND DISCUSSION The FPD and GS data presented in this manuscript (Table 1) represent a wide range in market age (36.9 to 58.2 d), placement density (0.07 to 0.10 m2/bird), finishing density (28.95 to 37.17 kg/m2), and slaughter weights (1.94 to 3.76 kg). The general distribution of FPD scores and GS remained about the same from yr to yr, with no significant difference between the yr within a complex (P > 0.05). Figures 1 and 2 represent the distribution of FPD and GS by production complex, respectively. The difference in distribution of FPD and GS between and within the 2 complexes was significantly different (P ≤ 0.0001). Complex B, which produced heavier broilers, had poorer FPD scores and GS than the lighter birds grown in complex A. This is a trend that has been reported previously [22, 38–40], although the differences found in previous studies from Europe were much greater than the results reported here. Factors that could lead to the difference in FPD and GS in birds of different ages include deterioration of litter quality and increased litter ammonia, moisture, and house humidity as the birds age [38]. Additionally, litter type has been identified as a factor that can influence incidence and severity of FPD [41]. For the specific complexes involved in this study, a greater percentage of farms in complex B used peanut hulls as their primary litter material vs. pine shavings. Complex A typically used more pine shavings than peanut hulls. Atencio and Opengart [42] showed that birds reared on peanut hulls had a greater incidence and severity of FPD than birds raised on pine shavings. Consequently, it is likely that litter type was an additional factor contributing to the greater incidence and severity of FPD in complex B. Figure 1. View largeDownload slide Foot pad dermatitis lesion score distribution by complex (2012-2014). Foot Pad lesion score distribution between complexes is different (P < 0.0001). Figure 1. View largeDownload slide Foot pad dermatitis lesion score distribution by complex (2012-2014). Foot Pad lesion score distribution between complexes is different (P < 0.0001). Figure 2. View largeDownload slide Gait score distribution by complex (2012-2014). Gait score distribution between complexes is different (P < 0.0001). Figure 2. View largeDownload slide Gait score distribution by complex (2012-2014). Gait score distribution between complexes is different (P < 0.0001). The incidence and severity of FPD and lameness reported in this study are lower than what has been previously reported, mostly from Europe. Based on the American Association of Avian Pathologists’ Broiler Paw Scoring Guide [13], >98% of the footpads in complex A and > 95% of the footpads in complex B would pass footpad evaluation (score 0 or 1). Several studies from the Netherlands, Denmark, and across Europe have reported severe FPD lesions (score 2) of 38.4, 13.1, and as high as 63%, respectively [39, 43, 44]. Differences in production practices may contribute to the reported differences in severity of FPD lesions. In many parts of Europe, e.g., flock thinning is practiced, where broilers are initially placed at high stocking densities [45], and a portion of the birds are removed for processing, allowing for additional floor space for the birds left in the house. Meluzzi et al., [45] reported placement density as tight as 0.055m2/bird in flocks that were to be thinned. While this practice may provide economic and commercial benefits, it may create an environment more likely to induce FPD. Young et al., [46] reported that FPD lesions formed relatively early in life, between 12 and 21 d, as litter conditions rapidly changed (increased total nitrogen, ammonia, and moisture). The incidence of FPD did not increase over the life of the flock in that study, indicating that the lesions that formed early may have remained as the birds aged. Placement density (m2/bird), therefore, may be a more important factor than finishing density (kg/m2) assuming other environmental factors that impact FPD remain constant. Dawkins et al., and Haslam et al. [7, 47] concluded that litter condition is more critical than stocking density in the development of FPD. We suggest that high stocking density contributing to poorer litter conditions early in a broiler's life may be a significant factor in FPD prevalence. Another factor that may account for some of the difference between FPD prevalence and severity is bedding source. As stated, the primary bedding material used in the current study was pine shavings, peanut hulls, or a mixture of both. Chopped straw is frequently used in Europe [8]. Several have reported that the incidence and severity of FPD is higher in birds raised on straw vs. pine shavings [40, 41, 48–50]. Other production factors that may contribute to the higher FPD lesions reported in Europe include (a) more impactful seasonal effect in certain parts of Europe [40, 45], (b) concrete floors in broiler houses, which can create condensation as well as act as a vapor barrier trapping moisture in litter compared with dirt floors typically found in broiler houses in the United States, and (c) relatively thin placement of bedding after complete clean-out after each flock in Europe as opposed to the deep, absorbent litter base of built-up litter common in U.S. production systems. Tables 2 and 3 represent the number and frequency of birds with various combinations of FPD and GS. These numbers serve as the basis for the odds calculation presented in Tables 4 to 7. Odds ratios (OR) were used to compare the probability, or likelihood, of association between the FPD scores and GS. Table 2. Percentage (total number) of birds within each FPD and gait score category for small birds (Complex A). Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) View Large Table 2. Percentage (total number) of birds within each FPD and gait score category for small birds (Complex A). Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) View Large Table 3. Percentage (total number) of birds within each FPD and gait score category for big birds (Complex B). Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) View Large Table 3. Percentage (total number) of birds within each FPD and gait score category for big birds (Complex B). Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) View Large Odds of a Change in GS with Changing FPD (Tables 4 and 5) FPD has been shown to have a negative impact on GS in some studies [51, 52], while other studies [53] have reported a lack of association. We found a strong relationship between FPD and GS in this study. In both complex A and complex B, the odds of higher GS increased with increasing FPD scores. The OR of FPD and GS were, however, varied by each production complex. This is likely due to a number of variables that differed between the 2 complexes that were not evaluated, such as bird age and weight at assessment, breed, farm management, litter type, and differences among individuals involved in scoring. As such, the scores from each location were not aggregated due to the potential of confounding variables between locations. Data indicated that GS was significantly lower in birds with FPD score of 0 than birds with FPD score of 1. Log OR of FPD 1 scored birds compared to FPD 0 birds (LogOR01) was statistically significant at Complex A (Table 4). Table 5 shows that this relationship exists in Complex B as well. Table 4 shows that the odds of having a lower GS are 1.7362 times higher for a bird having an FPD score of 0 compared to birds having an FPD score of 1 in Complex A. The odds of having a lower GS are 1.8711 times higher for a bird having an FPD score of 0 compared to birds having an FPD score of 1 in Complex B (Table 5). The larger OR in Complex B compared to Complex A suggest that bird size plays a role in the relationship between FPD and GS. This relationship has been described previously [22, 38, 39]. Table 4. Contrast estimate results for distribution of FPD for different levels of GS, Complex A Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 View Large Table 4. Contrast estimate results for distribution of FPD for different levels of GS, Complex A Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 View Large Table 5. Contrast estimate results for distribution of FPD for different levels of GS, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 View Large Table 5. Contrast estimate results for distribution of FPD for different levels of GS, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 View Large Table 6. Contrast estimate results for distribution of GS for different levels of FPD, Complex A. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 View Large Table 6. Contrast estimate results for distribution of GS for different levels of FPD, Complex A. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 View Large Table 7. Contrast estimate results for distribution of GS for different levels of FPD, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 View Large Table 7. Contrast estimate results for distribution of GS for different levels of FPD, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 View Large The odds of having a lower GS in birds having a 2 FPD score compared to birds having a 0 FPD score (LogOR02) at Complex A were not statistically significant (P > 0.05). The odds of having a lower GS in birds having a 2 FPD score compared to birds having a 1 FPD score (LogOR12) at Complex A were statistically significant. The odds of having a lower GS in birds having a 2 FPD score compared to birds having a 0 FPD score (LogOR02) at Complex B were statistically significant (Table 5). The odds of having a lower GS are 12.9811 times higher for a bird having an FPD score of 0 compared to birds having an FPD score of 2 in Complex B. Table 5 shows that the odds of having a lower GS in birds having a 2 FPD score compared to birds having a 1 FPD score (LogOR12) at Complex B were statistically significant. The odds of having a lower GS are 6.8897 times higher for a bird having an FPD score of 1 compared to birds having an FPD score of 2 in Complex B. This study confirms the previous reports that GS is negatively impacted by severe FPD [51, 52]. The negative impact of severe FPD on GS has been attributed to the pain associated with ulceration of the footpads [54, 55]. Improvements in gait by the administration of analgesics to birds with severe FPD have indirectly confirmed this relationship [56]. Odds of FPD with Changing GS (Tables 6 and 7) Our data indicated that as GS increased from 0, the odds of FPD increased in both complexes. The overall likelihood of poorer FPD scores due to GS changes was less in the small bird complex, suggesting, again, that bird size plays a role in the relationship between FPD and GS. The odds of having a lower FPD in birds having a 1 GS compared to birds having a 0 GS (LogOR01) at Complex A were statistically significant (Table 6). The odds of having a lower FPD are 1.7312 times higher for a bird having a GS of 0 compared to birds having a GS of 1 in Complex A. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 0 GS (LogOR02) at Complex A were statistically significant. The odds of having a lower FPD are 1.7019 times higher for a bird having a GS of 0 compared to birds having a GS of 2 in Complex A. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 1 GS (LogOR12) at Complex A were not statistically significant (P > 0.05). The odds of having a lower FPD in birds having a 1 GS compared to birds having a 0 GS (LogOR01) at Complex B were statistically significant (Table 7). The odds of having a lower FPD are 1.9632 times higher for a bird having a GS of 0 compared to birds having a GS of 1 in Complex B. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 0 GS (LogOR02) at Complex B were statistically significant. The odds of having a lower FPD are 6.7702 times higher for a bird having a GS of 0 compared to birds having a GS of 2 in Complex B. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 1 GS (LogOR12) at Complex B were statistically significant. The odds of having a lower FPD are 3.4485 times higher for a bird having a GS of 0 compared to birds having a GS of 2 in Complex B. The likelihood of worse FPD scores when GS increased from 0 to 2 in both complexes suggests that improvements in GS are associated with similar improvements in footpad condition. This does not necessarily indicate causation, but perhaps an association. The influence of GS on FPD has not been reported before in the literature, to the best of our knowledge. With this analysis, it is difficult to determine cause and effect, which may be confounding the risk assessment. It is far easier to explain how severe FPD can affect poor GS as opposed to how poor GS may cause severe FPD. Birds with poor mobility are more likely to sit than stand or walk and, therefore, would have more contact time with litter and be lighter in weight, eliminating some of the risk factors associated with poor GS and FPD [39]. CONCLUSIONS AND APPLICATIONS Over the course of this 3-year study, lighter broilers (∼2kgs) had significantly better FPD and GS than heavier broilers (∼3.7kgs). The relative incidence of severe FPD and GS (score 2) reported in this study is less than that reported from earlier studies from Europe. A number of environmental and management practices may contribute to this difference. There was a strongly significant association between FPD and GS within a complex. There were significantly greater odds of GS worsening as FPD worsened. There were also significantly high odds of FPD becoming more severe as GS worsened. Footnotes Primary Audience: Flock Supervisors, Production Managers, Veterinarians REFERENCES AND NOTES 1. Bessei W. 2006 . 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Google Scholar PubMed © 2018 Poultry Science Association Inc. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Poultry Research Oxford University Press

Incidence, severity, and relationship of broiler footpad lesions and gait scores of market-age broilers raised under commercial conditions in the southeastern United States

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Applied Poultry Science, Inc.
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© 2018 Poultry Science Association Inc.
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1056-6171
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1537-0437
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10.3382/japr/pfy002
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Abstract

SUMMARY The prevalence and severity of footpad dermatitis (FPD) and gait score (GS) as an indicator of lameness in commercial broiler production in the United States has not been widely reported. The objectives of this field study were to determine the prevalence and severity of FPD and lameness in commercial broilers, as well as the relationship between FPD and GS under the production conditions typical of the southeastern United States. Observations were collected from an integrated broiler complex producing a light broiler (1.94 to 2.22 kg) and an integrated broiler complex producing a heavier broiler (3.62 to 3.76 kg). Data were collected from 554 farms, 16,697 houses, and 166,977 broilers, representing over 328 million birds over the 3-year span of the study. Light broilers had significantly better FPD and GS than heavier broilers. Additionally, there was a strongly significant association between FPD and GS within a complex. There were significantly greater odds of GS worsening as FPD worsened and significantly high odds of FPD becoming more severe as GS worsened. DESCRIPTION OF PROBLEM In spite of tremendous advances in breeding, health, nutrition, and environmental control, footpad dermatitis (FPD) and lameness continue to be important welfare concerns facing the modern broiler industry [1–3]. Comprehensive information on the pathology and etiology of FPD [4–8] and lameness [9–11] in poultry has been published. Primary contributors to the development of FPD in poultry are the type of bedding material and high litter moisture. Gross FPD is usually categorized using a 3-point scale based on lesion severity [12, 13]. Lameness, on the other hand, has a more complex etiology involving both infectious and non-infectious causes [14]. Lameness has been scored kinetically by visually observing and categorizing the walking ability (i.e., gait) of broilers [15, 16]. A 3-point gait score (GS) system has been validated to assess overall leg health in commercial broiler flocks [17]. Although simple to implement and widely adapted to assess lameness, GS is subjective and not a very sensitive tool to discriminate if pain is involved with leg abnormalities and pathologies at the farm level [18, 19]. Reports from Europe indicate a high proportion of broilers with FPD and lameness [15, 20–22]. These studies are in contrast, however, to a recent study in which a steady improvement over time in leg health is reported in broilers [23]. The relationship between FPD and lameness as measured by GS is not clear. When present, abnormal gait was not associated with physiological stress or stress-associated pain [24, 25]. Reluctance to move was reported only in broilers exhibiting inflammatory FPD [26, 27]. Other studies could not demonstrate a correlation between FPD and GS under controlled experiments [28, 29]. The objectives of this field study were to determine the prevalence and severity of FPD and lameness in commercial broilers, as well as the relationship between FPD and GS under the production conditions typical of the southeastern United States—tunnel-ventilated, evaporative cooled, floor-raised broilers in which bedding material consists of at least 10 cm of pine shavings, peanut hulls, or some combination. While bedding is maintained at a depth of 10 cm, it is typically not totally removed after each flock; rather, the caked material is removed at the end of each flock, and new material is added back to maintain at least the 10 cm depth. MATERIALS AND METHODS Birds and Housing This study involved 2 commercial integrated broiler complexes in the southeastern United States from 2012 to 2014. One complex (A) produced a small broiler (1.94 to 2.22 kg), while the other (B) produced a heavier broiler (3.62 to 3.76 kg). A Hubbard M99 x Cobb 500 cross was used in complex A, and a Ross 344 x Ross 708 cross was used in complex B. Data were collected from 554 farms, 16,697 houses, and 166,977 broilers, representing over 328 million birds over the 3-year span of the study. Production volume and characteristics of each integrated complex for each yr are presented in Table 1. Table 1. Production characteristics. Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 View Large Table 1. Production characteristics. Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 Complex A Complex B 2012 2013 2014 2012 2013 2014 Slaughter volume (Mil./week) 0.985 1,150 1,190 1,270 1,270 1,270 Number of farms involved 62 60 69 125 118 120 Total number of houses sampled 1,418 2,195 2,350 3,660 3,583 3,491 Total number of broilers examined 14,184 21,949 23,502 36,600 35,833 34,909 Slaughter age (d) 36.9 37.9 38.7 58.2 55.5 56.9 Slaughter weight (kg) 1.94 2.12 2.22 3.73 3.62 3.76 Stocking density (m2/bird) 0.07 0.07 0.07 0.09 0.10 0.10 Stocking density (kg/m2) 30.47 28.95 29.15 35.06 36.13 37.15 View Large All commercial broiler houses assessed were of standard size (12 m x 152 m or larger), had power-assisted tunnel ventilation with 15 cm evaporative cooling pad systems, and were either curtain-sided, solid side-walled, or a combination of both. All houses had at least 4 lines of nipple drinkers and 2 feeder lines. Bedding material was allowed to build up and complete clean-out down to the dirt pad was done, on average, once per yr per house. If complete clean-out of a house was not completed, caked bedding material was removed from the house, and fresh bedding material was added back to attain at least 10 cm dry, un-caked litter base. Bedding material consisted of peanut hulls, pine shavings, or a combination of the 2 materials. Broilers received a standard 4-stage diet consisting of starter, grower, finisher, and withdrawal feeds. The general nutritional plan for each feed between complexes was similar with the major difference being the feed quantity of each specific feed type provided to the bird based on the age of processing within each complex. Generally speaking, both complexes provided approximately the same amount of starter feed, but complex B provided 2 to 3 times more grower, finisher, and withdrawal feeds per bird. Measures As part of their normal flock service visit and animal welfare verification checks [30], trained company flock service technicians examined 10 randomly selected broilers per house for FPD [31] and GS [32, 33] 7 to 10 d prior to processing. In order to assess the relationship between FPD and GS, each of the 10 birds per house was scored for both attributes, and the data for each bird were linked. Statistics The 1st ordinal logistic model was used to compare FPD and GS distribution by production complex. Distribution of FPD and GS was analyzed using the GLIMMIX procedure of SAS®, version 9.3 or later [34, 35]. The association between FPD and GS was analyzed using the FREQ procedure of SAS® [36]. The 2nd ordinal logistic model compared the distribution of FPD score for different levels of GS by complex. The 3rd ordinal logistic model compared the distribution of GS for different levels of FPD by complex. Both the 2nd and 3rd ordinal logistic models were analyzed using the GENMOD procedure of SAS® [37]. RESULTS AND DISCUSSION The FPD and GS data presented in this manuscript (Table 1) represent a wide range in market age (36.9 to 58.2 d), placement density (0.07 to 0.10 m2/bird), finishing density (28.95 to 37.17 kg/m2), and slaughter weights (1.94 to 3.76 kg). The general distribution of FPD scores and GS remained about the same from yr to yr, with no significant difference between the yr within a complex (P > 0.05). Figures 1 and 2 represent the distribution of FPD and GS by production complex, respectively. The difference in distribution of FPD and GS between and within the 2 complexes was significantly different (P ≤ 0.0001). Complex B, which produced heavier broilers, had poorer FPD scores and GS than the lighter birds grown in complex A. This is a trend that has been reported previously [22, 38–40], although the differences found in previous studies from Europe were much greater than the results reported here. Factors that could lead to the difference in FPD and GS in birds of different ages include deterioration of litter quality and increased litter ammonia, moisture, and house humidity as the birds age [38]. Additionally, litter type has been identified as a factor that can influence incidence and severity of FPD [41]. For the specific complexes involved in this study, a greater percentage of farms in complex B used peanut hulls as their primary litter material vs. pine shavings. Complex A typically used more pine shavings than peanut hulls. Atencio and Opengart [42] showed that birds reared on peanut hulls had a greater incidence and severity of FPD than birds raised on pine shavings. Consequently, it is likely that litter type was an additional factor contributing to the greater incidence and severity of FPD in complex B. Figure 1. View largeDownload slide Foot pad dermatitis lesion score distribution by complex (2012-2014). Foot Pad lesion score distribution between complexes is different (P < 0.0001). Figure 1. View largeDownload slide Foot pad dermatitis lesion score distribution by complex (2012-2014). Foot Pad lesion score distribution between complexes is different (P < 0.0001). Figure 2. View largeDownload slide Gait score distribution by complex (2012-2014). Gait score distribution between complexes is different (P < 0.0001). Figure 2. View largeDownload slide Gait score distribution by complex (2012-2014). Gait score distribution between complexes is different (P < 0.0001). The incidence and severity of FPD and lameness reported in this study are lower than what has been previously reported, mostly from Europe. Based on the American Association of Avian Pathologists’ Broiler Paw Scoring Guide [13], >98% of the footpads in complex A and > 95% of the footpads in complex B would pass footpad evaluation (score 0 or 1). Several studies from the Netherlands, Denmark, and across Europe have reported severe FPD lesions (score 2) of 38.4, 13.1, and as high as 63%, respectively [39, 43, 44]. Differences in production practices may contribute to the reported differences in severity of FPD lesions. In many parts of Europe, e.g., flock thinning is practiced, where broilers are initially placed at high stocking densities [45], and a portion of the birds are removed for processing, allowing for additional floor space for the birds left in the house. Meluzzi et al., [45] reported placement density as tight as 0.055m2/bird in flocks that were to be thinned. While this practice may provide economic and commercial benefits, it may create an environment more likely to induce FPD. Young et al., [46] reported that FPD lesions formed relatively early in life, between 12 and 21 d, as litter conditions rapidly changed (increased total nitrogen, ammonia, and moisture). The incidence of FPD did not increase over the life of the flock in that study, indicating that the lesions that formed early may have remained as the birds aged. Placement density (m2/bird), therefore, may be a more important factor than finishing density (kg/m2) assuming other environmental factors that impact FPD remain constant. Dawkins et al., and Haslam et al. [7, 47] concluded that litter condition is more critical than stocking density in the development of FPD. We suggest that high stocking density contributing to poorer litter conditions early in a broiler's life may be a significant factor in FPD prevalence. Another factor that may account for some of the difference between FPD prevalence and severity is bedding source. As stated, the primary bedding material used in the current study was pine shavings, peanut hulls, or a mixture of both. Chopped straw is frequently used in Europe [8]. Several have reported that the incidence and severity of FPD is higher in birds raised on straw vs. pine shavings [40, 41, 48–50]. Other production factors that may contribute to the higher FPD lesions reported in Europe include (a) more impactful seasonal effect in certain parts of Europe [40, 45], (b) concrete floors in broiler houses, which can create condensation as well as act as a vapor barrier trapping moisture in litter compared with dirt floors typically found in broiler houses in the United States, and (c) relatively thin placement of bedding after complete clean-out after each flock in Europe as opposed to the deep, absorbent litter base of built-up litter common in U.S. production systems. Tables 2 and 3 represent the number and frequency of birds with various combinations of FPD and GS. These numbers serve as the basis for the odds calculation presented in Tables 4 to 7. Odds ratios (OR) were used to compare the probability, or likelihood, of association between the FPD scores and GS. Table 2. Percentage (total number) of birds within each FPD and gait score category for small birds (Complex A). Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) View Large Table 2. Percentage (total number) of birds within each FPD and gait score category for small birds (Complex A). Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) Footpad dermatitis score Gait score 0 1 2 GS total 0 20.41% (34,101) 6.88% (11,486) 0.40% (661) 27.68% (46,248) 1 4.89% (8159) 2.89% (4826) 0.15% (257) 7.93% (13,242) 2 0.10% (163) 0.08% (48) 0.01% (14) 0.13% (225) FPD total 42.23% (42,423) 6.43% (16,360) 0.37% (932) 100% (59,715) View Large Table 3. Percentage (total number) of birds within each FPD and gait score category for big birds (Complex B). Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) View Large Table 3. Percentage (total number) of birds within each FPD and gait score category for big birds (Complex B). Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) Footpad dermatitis score Gait score 0 1 2 GS total 0 24.78% (41,397) 16.03% (26,780) 1.25% (2088) 42.06% (70,265) 1 8.45% (14,118) 10.74% (17,942) 0.75% (1246) 19.94% (33,306) 2 0.54% (899) 0.83% (1391) 0.89% (1481) 2.26% (3771) FPD total 22.18% (56,414) 18.13% (46,113) 1.89% (4815) 100 (107,342) View Large Odds of a Change in GS with Changing FPD (Tables 4 and 5) FPD has been shown to have a negative impact on GS in some studies [51, 52], while other studies [53] have reported a lack of association. We found a strong relationship between FPD and GS in this study. In both complex A and complex B, the odds of higher GS increased with increasing FPD scores. The OR of FPD and GS were, however, varied by each production complex. This is likely due to a number of variables that differed between the 2 complexes that were not evaluated, such as bird age and weight at assessment, breed, farm management, litter type, and differences among individuals involved in scoring. As such, the scores from each location were not aggregated due to the potential of confounding variables between locations. Data indicated that GS was significantly lower in birds with FPD score of 0 than birds with FPD score of 1. Log OR of FPD 1 scored birds compared to FPD 0 birds (LogOR01) was statistically significant at Complex A (Table 4). Table 5 shows that this relationship exists in Complex B as well. Table 4 shows that the odds of having a lower GS are 1.7362 times higher for a bird having an FPD score of 0 compared to birds having an FPD score of 1 in Complex A. The odds of having a lower GS are 1.8711 times higher for a bird having an FPD score of 0 compared to birds having an FPD score of 1 in Complex B (Table 5). The larger OR in Complex B compared to Complex A suggest that bird size plays a role in the relationship between FPD and GS. This relationship has been described previously [22, 38, 39]. Table 4. Contrast estimate results for distribution of FPD for different levels of GS, Complex A Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 View Large Table 4. Contrast estimate results for distribution of FPD for different levels of GS, Complex A Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.5517 0.0206 0.05 0.5113 0.5922 714.79 <.0001 GS 0 vs. GS 2 0.1325 0.1506 0.05 −0.1627 0.4276 0.77 0.379 GS 1 vs. GS 2 −0.4192 0.1513 0.05 −0.7157 −0.1228 7.68 0.0056 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.7362 0.0358 0.05 1.6674 1.8079 GS 0 vs. GS2) 1.1416 0.1719 0.05 0.8499 1.5336 GS 1 vs. GS 2 0.6575 0.0995 0.05 0.4889 0.8844 View Large Table 5. Contrast estimate results for distribution of FPD for different levels of GS, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 View Large Table 5. Contrast estimate results for distribution of FPD for different levels of GS, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted FPD scores comparing GS 0 vs. GS 1 0.6265 0.0131 0.05 0.6008 0.6522 2287.4 <.0001 GS 0 vs. GS 2 2.5565 0.038 0.05 2.482 2.631 4524.1 <.0001 GS 1 vs. GS 2 1.93 0.0385 0.05 1.8546 2.0054 2518.1 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) GS 0 vs. GS 1 1.8711 0.0245 0.05 1.8236 1.9197 GS 0 vs. GS2 12.8911 0.49 0.05 11.9657 13.8881 GS 1 vs. GS 2 6.8897 0.265 0.05 6.3894 7.4292 View Large Table 6. Contrast estimate results for distribution of GS for different levels of FPD, Complex A. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 View Large Table 6. Contrast estimate results for distribution of GS for different levels of FPD, Complex A. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.5488 0.021 0.05 0.5077 0.59 683.37 <.0001 FPD 0 vs. FPD 2 0.5318 0.0732 0.05 0.3883 0.6753 52.74 <.0001 FPD 1 vs. FPD 2 −0.017 0.0742 0.05 −0.1624 0.1284 0.05 0.8184 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.7312 0.0363 0.05 1.6614 1.8039 FPD 0 vs. FPD 2 1.7019 0.1246 0.05 1.4744 1.9646 FPD 1 vs. FPD 2 0.9831 0.0729 0.05 0.8501 1.137 View Large Table 7. Contrast estimate results for distribution of GS for different levels of FPD, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 View Large Table 7. Contrast estimate results for distribution of GS for different levels of FPD, Complex B. Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 Label L’Beta Estimate Standard Error Alpha L’Beta Confidence Limits Chi-Square Pr > ChiSq Contrasted GS scores comparing FPD 0 vs. FPD 1 0.6746 0.0133 0.05 0.6486 0.7006 2582.6 <.0001 FPD 0 vs. FPD 2 1.9125 0.0333 0.05 1.8473 1.9778 3299.1 <.0001 FPD 1 vs. FPD 2 1.2379 0.0332 0.05 1.173 1.3029 1394.3 <.0001 Odds Ratio (Odds of Lower Order FPD Score when comparing) FPD 0 vs. FPD 1 1.9632 0.0261 0.05 1.9128 2.015 FPD 0 vs. FPD 2 6.7702 0.2254 0.05 6.3425 7.2267 FPD 1 vs. FPD 2 3.4485 0.1143 0.05 3.2316 3.6801 View Large The odds of having a lower GS in birds having a 2 FPD score compared to birds having a 0 FPD score (LogOR02) at Complex A were not statistically significant (P > 0.05). The odds of having a lower GS in birds having a 2 FPD score compared to birds having a 1 FPD score (LogOR12) at Complex A were statistically significant. The odds of having a lower GS in birds having a 2 FPD score compared to birds having a 0 FPD score (LogOR02) at Complex B were statistically significant (Table 5). The odds of having a lower GS are 12.9811 times higher for a bird having an FPD score of 0 compared to birds having an FPD score of 2 in Complex B. Table 5 shows that the odds of having a lower GS in birds having a 2 FPD score compared to birds having a 1 FPD score (LogOR12) at Complex B were statistically significant. The odds of having a lower GS are 6.8897 times higher for a bird having an FPD score of 1 compared to birds having an FPD score of 2 in Complex B. This study confirms the previous reports that GS is negatively impacted by severe FPD [51, 52]. The negative impact of severe FPD on GS has been attributed to the pain associated with ulceration of the footpads [54, 55]. Improvements in gait by the administration of analgesics to birds with severe FPD have indirectly confirmed this relationship [56]. Odds of FPD with Changing GS (Tables 6 and 7) Our data indicated that as GS increased from 0, the odds of FPD increased in both complexes. The overall likelihood of poorer FPD scores due to GS changes was less in the small bird complex, suggesting, again, that bird size plays a role in the relationship between FPD and GS. The odds of having a lower FPD in birds having a 1 GS compared to birds having a 0 GS (LogOR01) at Complex A were statistically significant (Table 6). The odds of having a lower FPD are 1.7312 times higher for a bird having a GS of 0 compared to birds having a GS of 1 in Complex A. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 0 GS (LogOR02) at Complex A were statistically significant. The odds of having a lower FPD are 1.7019 times higher for a bird having a GS of 0 compared to birds having a GS of 2 in Complex A. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 1 GS (LogOR12) at Complex A were not statistically significant (P > 0.05). The odds of having a lower FPD in birds having a 1 GS compared to birds having a 0 GS (LogOR01) at Complex B were statistically significant (Table 7). The odds of having a lower FPD are 1.9632 times higher for a bird having a GS of 0 compared to birds having a GS of 1 in Complex B. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 0 GS (LogOR02) at Complex B were statistically significant. The odds of having a lower FPD are 6.7702 times higher for a bird having a GS of 0 compared to birds having a GS of 2 in Complex B. The odds of having a lower FPD in birds having a 2 GS compared to birds having a 1 GS (LogOR12) at Complex B were statistically significant. The odds of having a lower FPD are 3.4485 times higher for a bird having a GS of 0 compared to birds having a GS of 2 in Complex B. The likelihood of worse FPD scores when GS increased from 0 to 2 in both complexes suggests that improvements in GS are associated with similar improvements in footpad condition. This does not necessarily indicate causation, but perhaps an association. The influence of GS on FPD has not been reported before in the literature, to the best of our knowledge. With this analysis, it is difficult to determine cause and effect, which may be confounding the risk assessment. It is far easier to explain how severe FPD can affect poor GS as opposed to how poor GS may cause severe FPD. Birds with poor mobility are more likely to sit than stand or walk and, therefore, would have more contact time with litter and be lighter in weight, eliminating some of the risk factors associated with poor GS and FPD [39]. CONCLUSIONS AND APPLICATIONS Over the course of this 3-year study, lighter broilers (∼2kgs) had significantly better FPD and GS than heavier broilers (∼3.7kgs). The relative incidence of severe FPD and GS (score 2) reported in this study is less than that reported from earlier studies from Europe. A number of environmental and management practices may contribute to this difference. There was a strongly significant association between FPD and GS within a complex. There were significantly greater odds of GS worsening as FPD worsened. There were also significantly high odds of FPD becoming more severe as GS worsened. Footnotes Primary Audience: Flock Supervisors, Production Managers, Veterinarians REFERENCES AND NOTES 1. Bessei W. 2006 . 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Journal of Applied Poultry ResearchOxford University Press

Published: Apr 11, 2018

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