Influence of broiler strain cross and dietary protein on the performance of broilers.

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 x Ross 208) and a fast-growing strain cross (Peterson x 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 x 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 x Ross 208 than for the Peterson x 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 profitability.