COMMERCIAL APPROACHES TO GENETIC SELECTION FOR GROWTH AND FEED CONVERSION IN DOMESTIC POULTRY

Tremendous genetic progress has been observed historically for growth and feed conversion through the efforts of the primary breeding compan ies. However, significant between-strain variation still exists due to differences in selection emphasis and selection techniques practiced by these organizations. This paper provides an overview of methods cur rently employed in commercial poultry breeding with reference to facto rs complicating program design and future challenges facing the indust ry. Mass selection for body weight has resulted in a significant reduc tion in the number of days required to grow bird to market weight with indirect improvements in feed conversion. Direct selection for feed c onversion is accomplished through part record testing of males that ha ve been preselected for body weight, conformation, and defect traits. Data are commonly subjected to complex statistical analysis both to co rrect feed conversion for variation in body weight and to improve the accuracy of breeding value estimates. Feed conversion breeding values of male sibs are sometimes used for the selection of female candidates as well. Selection for growth rate and efficiency has resulted in neg ative complications, such as ascites, reduced reproductive performance , skeletal abnormalities, and increased carcass fatness. Some of these factors may be partially ameliorated through modified selection pract ices. If not addressed by the breeding industry, the disruption of phy siological homeostasis might ultimately represent economic and genetic barriers to further progress in improving growth and efficiency. Mode rn techniques in molecular genetics, utilized in conjunction with trad itional quantitative genetic approaches, will provide additional oppor tunities to circumvent these physiological complications associated wi th genetic selection for growth and feed efficiency.