The magnitude and nature of changes in performance of the chicken

The authors summarize the magnitude and nature of the improvement of produc tion traits in layers and broilers based on the results of international st rain comparisons conducted in Hungary and other European countries, Layer h ibrids showed an annual improvement exceeding 2 eggs/hen in the last two de cades. Brown egg layers improved more rapidly in feed efficiency compared t o leghorns (-0,6 kg feed/egg kg for the browns, -0,5 kg/egg kg for leghorns ), mainly due to improved egg production and reduced body weight. Today lay ers start to lay 15-20 days earlier than 20 years ago. Weight gain of broilers improved by 30% for males, and 40% in females in th e last 20 years comparing both the best individual and pen mean performance s (49 day body weight). As a correlated response, broiler males reach 6 kg live weight 7 weeks earlier compared to broilers of the 1980s, in females t he difference is even greater. In layer type hens selection for egg product ion traits did not lead to negatively correlated responses regarding vitali ty related characteristics, Selection for Improved growth rate in broiler p opulations resulted in a decreased adaptiveness to various unfavourable env ironmental conditions.