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276 - METABOLISM AND NUTRITION Influence of Broiler Strain...

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276 METABOLISM AND NUTRITION Received for publication March 24, 1997. Accepted for publication September 22, 1997. 1 Supported by state and Hatch funds allocated to the Georgia Agricultural Stations of The University of Georgia. 2 To whom correspondence should be addressed: [email protected] uga.edu Abbreviation Key: FCR = feed conversion ratio. Influence of Broiler Strain Cross and Dietary Protein on the Performance of Broilers 1 E. R. SMITH and G. M. PESTI 2 Department of Poultry Science, The University of Georgia, Athens, Georgia 30602-2772 ABSTRACT The purpose of this experiment was to quantify the responses of two broiler strain crosses to different dietary protein levels on performance and carcass yields. Day-old broiler chicks from a high-yield strain cross (Ross × Ross 208) and a fast-growing strain cross (Peterson × Arbor Acres) were placed in floor pens on fresh pine shavings. All birds were fed a 23% CP starter for the first 18 d. During Days 18 to 53, birds were fed either 16, 20, or 24% CP diets (3,200 kcal ME/ kg). At 53 d of age, significant differences ( P < 0.05) were noted in the performance of the strains. Overall, Ross × Ross birds had higher body weights (3.29 vs 3.10 kg), higher feed intakes (6.40 vs 6.11 kg), and higher carcass yields (72.51 vs 71.17%), although the differences were dependent on dietary protein levels. Strain cross had no significant effect on feed conversion (1.95 g feed: g gain vs 1.97 g:g). Results indicated that both strain cross and protein level had effects on body weight and feed intake, and there were significant strain cross by protein level interactions for body weight and carcass weight. Increasing dietary protein level increased body weights more for the Ross × Ross 208 than for the Peterson × Arbor Acres broilers. Feed conversion was indirectly proportional to dietary protein level, but was not affected by strain cross. Percentage carcass yield was greatly affected by strain ( P < 0.0001), but protein level had no significant effect ( P = 0.68). The significant interactions indicate that different strain crosses should have different feeding programs to maximize profitabil- ity. ( Key words : carcass yield, broiler, abdominal fat pad, strain, dietary protein) 1998 Poultry Science 77:276–281 INTRODUCTION Genetics have been shown to have a major impact on the growth rate of broiler chicks. A relationship has been reported between feed protein level and genotype (Leclerq, 1983; Marks and Pesti, 1984; Cahaner et al ., 1987). Hulan et al . (1980) showed that genotype affects the feed conversion ratios (FCR; grams feed consumed per gram body weight change). This effect could be due to a decreased feed intake for the same gain or increased body weight for the same amount of feed or a combination of the two. Genetics have also been found to play a role in the abdominal fat pad weight of broilers (Jackson et al ., 1982; Leclerq, 1983; Marks and Pesti, 1984; Barbato, 1992). A variance in carcass yield due to genetics was found by Renden et al . (1992). Evans et al .
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