Influence of strain-cross, sex, and feeding programs on broiler chicken paw (feet) yield and quality

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1 Influence of strain-cross, sex, and feeding programs on broiler chicken paw (feet) yield and quality S.F. BILGILI*, M.A. ALLEY, J.B. HESS and E.T. MORAN, JR. Department of Poultry Science, 201 Poultry Science Building, 260 Lem Morrison drive, Auburn University, Auburn, Alabama , USA Keywords: foot; paw; broilers; strain-cross; yield Summary In two separate experiments (Exp), the effects of strain-cross (SC), sex, and feeding programs on foot quality and yields were determined. In Exp 1, male broilers from four SC were reared to 49 days of age on low and high energy feeding programs. In Exp 2, male and female broilers from two SC were reared to 42 days of age on four diverse feeding programs used by the commercial broiler industry. In each experiment, feet were separated during processing at the hock joint after defeathering, weighed, and visually scored for the incidence and severity of pigmentation and foot pad dermatitis. Strain-cross was a significant (P<0.05) factor in foot weight and pigmentation (Exp 1). However, no differences due to SC were detected in paw yields. As expected, birds reared on low energy feeding programs had significantly higher foot yields than those reared on high energy program. Foot pad dermatitis did not vary by the two feeding programs in Exp 1. Significant SC and sex effects were present for foot yields in Exp 2. The incidence and severity of foot pad dermatitis was higher in males than females, but did not vary by SC. Foot pad dermatitis varied significantly among the feeding programs used. Overall, the pigmentation of the feet was correlated to genetics. On the other hand, the incidence and severity of foot pad dermatitis was attributed to the nutrient density of the diets. Introduction The chicken paw, or portion of the feet just below the spur, has been transformed from a low-value byproduct into a highly profitable export item for the broiler industry (Christensen, 1996; Bilgili and Hess, 1997). Factors affecting the quality and safety of paws have recently become an economic, as well as a welfare concern for the industry (NCC, 2003). The market value of chicken feet is determined by both size (weight) and quality (grade). Size of the feet creates a price differential from small to large, with jumbo paws having the highest value. Quality factors for paws include pigmentation, fractures, bruises, calluses and foot pad dermatitis (Brown et al., 1996). Foot pad dermatitis ranges in severity from mild irritation of the skin (usually removed during scalding and picking) to deep ulcers. Foot pad lesions influenced by several production conditions and practices. High stocking densities and wet litter is the single largest contributor to fad pad dermatitis. Flock management, including ventilation, evaporative cooling and drinker adjustments, correlate with litter moisture in the chicken house (Hester, 1994). Nutritional programs can also affect foot pad dermatitis. High protein feeds lead to increased nitrogen excretion and more food pad dermatitis (Abbott et al, 1969). High levels of dietary potassium, magnesium and sodium can contribute to wet litter through increased water consumption. Harms and Simpson (1975) and Harms et al. (1977) have shown biotin deficiency as a contributing factor to foot pad swelling and ulcerations. Market age is another important factor, as increasing quantities of moisture and nitrogen are excreted into the litter. In this study, the influence of strain-cross, sex and feeding program on paw quality in broiler chickens was investigated. 342

2 Materials and methods EXPERIMENT male broiler chickens from four commercial strain-crosses (SC; designated as A, B, C, and D) were placed in a curtain-sided, naturally ventilated, concrete floored house (32 pens total; 8 pens per SC; 25 birds per pen). One-half of the replicate pens (1.7 x 2.3 m; 6.4 kg per sq. meter) for each SC were placed on a high energy feeding (3187 kcal/kg ME) program, while the other half received a low energy (3086 kcal/kg ME) program. Both feeding programs were designed and formulated with similar nutrient profiles that meet the NRC (1994 ) requirements for broilers (Table 1). A three stage feeding program, consisting of a starter (1-21 days), grower (22-42 days) and finisher period (43-49 days) was utilized. Birds were reared on a 23:1 h L:D (Light:Dark) lighting program. Feed and water was provided continuously. All birds were weighed and processed at the end of the experiment. EXPERIMENT sexed broiler chickens from two commercial SC were placed in 32 pens (16 pens per SC; 25 males and 25 females per pen) and reared to 42 days of age. A total of eight pens (four per SC; 12.8 birds per sq. meter) were assigned to four commercially used feeding programs. Feeding programs (designated from 1-4) consisted of three stages (starter, grower and finisher), but varied greatly in nutrient content and total days fed (Table 2). Birds were reared on a 23:1 h L:D program. Feed and water was provided continuously. All birds were weighed individually at the end of the experiment and 30 birds were randomly chosen from each pen (960 total) for processing. PROCESSING Birds from both experiments were processed at the Auburn University Pilot Processing Plant. Feed was withdrawn for about 10 h prior to processing. After scalding and defeathering, the feet were separated at the hock joint and chilled in static ice. The entire feet, rather than the shorter paw portion, were used to determine yields for consistency. Foot was weighed and foot yields, as a proportion of live weight, was calculated. Shank lengths were also recorded. Feet were visually evaluated for presence or absence of pigmentation and also scored for severity of foot pad dermatitis. The visual scoring system consisted of 0 for no lesions, 1 for mild lesions of <7.5 mm in diameter, and a score of 2 for lesions >7.5 mm. STATISTICAL ANALYSIS Data form both experiments were analyzed using the General linear Models procedure of SAS (1988). Experiment 1 was analyzed as a 4x2 arrangement of SC and feeding programs, with replicate pens serving as the error term to test the main effects and interactions. Experiment 2 was analyzed as a 2x4 arrangement of SC and feeding programs, with sex nested within replicate pens. Sex by replicate pen interaction was used as an error term to test the main effects and their interactions. When significant (P<0.05), means were separated using the Tukey s test. Results and discussion Live body weights and shank lengths did not vary among the SC and diet energy levels in Experiment 1 (Table 3). However, significant differences were observed for foot weights for SC and foot yields for diet energy levels. Birds reared on low energy diets had higher foot yields (3.60%) than those on high energy diets (3.47%). No foot pad dermatitis was detected in this study. The favourable rearing conditions (i.e., new litter and low stocking density) may have prevented the lesions from developing. The foot pigmentation significantly varied by SC (Figure 1). This was expected, as the presence of melanin pigmentation is an inherited trait in broiler chickens. In contrast to Experiment 1, significant SC, sex and feeding program effects were present for live weights and foot yields in Experiment 2 (Table 4). Males had higher body and foot weights than females. Body weights and foot yields also differed between the two SC. Feeding programs did not affect foot yields. The incidence and severity of foot pad lesions varied significantly among the four feeding programs tested and paralleled the nutrients density levels (Table 5). The severity of foot pad lesions only varied by sex (males>females). 343

3 Overall, the chicken paw downgrading factors, such pigmentation and dermatitis can directly be attributed to the live production phase. The results of this study confirms the field observations that genetics plays a major role in shank pigmentation and that feeding programs (i.e., nutrient density) may be a significant factor in the etiology of foot pad lesions. References ABBOTT, W.W., COUCH, J.R. and ATKINSON, R.L. (1969) The incidence of foot pad dermatitis in young turkeys fed high levels of soybean meal. Poultry Sci. 48: BILGILI, S.F., and HESS, J.B. (1997). Maximizing chicken paw yield and quality. Meat and Poultry 43(5):54. BROWN, H.G., ZELENKA, D.J., AND REINHART-JONES, L. (1996) Effects of breed, sex, age and size on quality and value of chicken paws. Poultry Sci. 75:24. CHRISTENSEN, H. (1996). PRESTO! An insatiable market in southern China and Hong Kong changes a chicken by-product into a snack food. Poultry Marketing and Technology. April/May p HARMS, R.H. and SIMPSON, C.F. (1975) Biotin deficiency as a possible cause of swelling and ulceration of foot pads. Poultry Sci. 54: HARMS, R.H., DAMRON, B.L., and SIMPSON, C.F. (1977). Effect of wet litter and supplemental biotin and/or whey on the production of foot pad dermatitis in broilers. Poultry Sci. 56: HESTER, P.Y. (1994) The role of environment and management on leg abnormalities in meat-type fowl. Poultry Sci. 73: NATIONAL CHICKEN COUNCIL (2003) Animal welfare guidelines and audit checklist. National Chicken council, Washington, DC. NATIONAL RESEARCH COUNCIL (1994) Nutrient requirements of poultry, ninth revised edition. National Academy Press. Washington, D.C. SAS INSTITUTE (1988) SAS/STAT Users Guide for Personal Computers, release SAS Institute, Raleigh, NC. Table 1 Composition of Experimental Diets: High and Low Energy Feeding Programs (Experiment 1) 1. Starter Grower Finisher Ingredients High Low High Low High Low ME (kcal/kg) Protein (%) Lysine (%) Calcium (%) Phosphorus (%) 1 Birds grown to 49 days of age

4 Table 2 Composition of Feeding Programs (Experiment 2). Program 1 2 Program 2 Program 3 Program 4 Ingredients ST 3 GR 4 FR 5 ST GR FR ST GR FR ST GR FR ME (kcal/kg) Protein (%) Lysine (%) TSAA (%) Days Fed Birds grown to 42 days of age 2 Commercial feeding programs used in the study 3 ST = Starter period 4 GR = Grower period 5 FR=Finisher period TSAA= Total sulphur amino acids. 345

5 Table 3 Influence of Strain-cross and Feeding Program on Live Body Weight, Foot Weight and Yield (Experiment 1) 1. Foot Treatment Body Weight (g) Weight (g) Yield (%) Shank Length (cm) Strain-cross NS * NS NS A b B a C ab D ab SEM Feed Program 2 NS NS ** NS HE a 8.12 LE b 8.07 SEM Interaction NS NS NS NS 1 Birds grown to 49 days of age 2 HE=High energy; LE= low energy NS= not significant (P>0.05) SEM= Pooled standard error of the mean. 346

6 Table 4 Influence of Strain-cross, Sex, and Feeding Program on Body Weight, Foot Weight and Yield (Experiment 2) 1. Foot Treatment Body Weight (g) Weight (g) Yield (%) Strain-cross *** NS ** A 2245 a b B 2160 b a Sex *** *** *** Male 2353 a a 4.43 a Female 2052 b 76.1 b 3.71 b SEM Feed Program *** *** NS ab 90.5 a a 93.5 a b 89.8 ab c 86.8 b 4.11 SEM Interaction NS NS NS 1 Birds grown to 42 days of age 2 Numbers denote different commercial feeding programs used in the study NS= Not significant (P>0.05) SEM= Pooled standard error of the mean. * P<0.05; **P<0.01; ***P<

7 Table 5 Influence of Strain-Cross, Sex, and Feeding Program on the incidence of Foot pad lesions (Experiment 2) 1. Foot Pad Lesion (%) Treatment None Mild Severe Strain-cross NS NS NS A B Sex NS NS * Male a Female b SEM SEM Feed Program ** * ** a 29.1 ab 5.4 ab b 45.4 a 18.6 a ab 34.2 ab 7.3 b a 23.1 b 3.7 b Interaction NS NS NS 1 Birds grown to 42 days of age 2 Numbers denote different commercial feeding programs used in the study NS= not significant (p>0.05) SEM= Pooled standard error of the mean. *P<0.05; **P<0.01; ***P<

8 16 14 % Birds with Pigmentation A B C D Strain-Cross Figure 1 Strain-cross differences in shank pigmentation in Experiment 1 (SEM=2.6). 349