Genetic Changes in Meat-Type Chickens in the Last Twenty Years

Three experimental strains and two modern commercial stocks of meat-type chickens were compared in 1978. One experimental strain, K, an unselected control, represented broilers of 20 yr ago. A second experimental strain, A, selected for high broiler weight and a third, D, selected for high broiler and low adult weights had been derived from strain K and represented experimental strains genetically improved by artificial selection. All stocks were hatched and reared simultaneously using modern industrial practices. At 47 days, 70 birds of each sex and stock were slaughtered and the carcasses chemically analyzed. Also, 25 hens of each of strains A, D and K were slaughtered when 68 wk old and abdominal fat and carcass weight data were analyzed. The selection for higher broiler weight in strain A increased both broiler and adult body weights more and percent carcass fat less than the selection for high broiler and low adult weight in strain D. Relative to strain A, carcass weight of strain D was 10% lower in broilers and 16% lower in adult hens. Respective means for the modern commercial broilers, strain A broilers, and "broilers of 20 years ago" were 1552, 1001 and 676 g dressed carcass weight; 2.4, 1.6 and 1.4% abdominal fat; 17.2, 15.4 and 12.4% carcass fat (wet basis) and 1.90, 1.92 and 2.01 feed conversion. Thus, the modern broilers have a dramatically increased growth rate accompanied by higher fat content. The greater fat deposition may at least partly account for the lack of significant improvement in feed conversion.