Dietary amino acid density effects on growth and carcass of broilers differing in strain cross and sex

Some broiler integrators in the United States commonly reduce diet nutrient density as a way of reducing overall diet cost because feed represents the majority of live production costs. There is disagreement about amino acid feeding regimens for broilers, particularly when raising heavy broilers for maximum carcass and breast meat yields. Two experiments evaluated the effect of feeding a nutritional program similar to that currently used by the US poultry industry (low amino acid density; LD) and an isocaloric program with higher amino acid levels (high amino acid density; HD) on the performance of broilers varying in sex and strain cross (1 high-yield strain and 2 multipurpose strains). Data from both experiments were pooled because no interactions between trials were noted. Broilers fed HD diets had increased BW and decreased feed conversion (g of feed/g of gain) throughout all phases of the study when compared with broilers fed LD diets. Males had higher BW and lower feed conversion than females. Mortality was unaffected by diet type, strain, or sex. Broilers of the high-yield strain had lower BW and higher feed conversions when compared with the 2 multipurpose strains. Broilers fed HD diets resulted in lower abdominal fat percentage, as well as higher fillet and tender yields at 42 and 56 d of age. No effect of dietary regimen was observed for yield of carcass, wings, drums, or saddle. Carcasses from female broilers typically had higher percentages of fat and wings and lower drum and saddle yields. The high-yield strain had higher percentages of fillets, tenders and carcass and lower fat and saddle yields when compared with the multipurpose strains. Overall improvements in economically important parameters (i.e., feed conversion, and white meat yield) observed after feeding an amino acid concentration greater than that typically used by some broiler integrators in the US suggest that industry standard nutritional programs may be low in amino acids. Considerations for increasing current amino acid concentrations should be made on a cost-benefit basis.