Heritability Estimates for Juvenile Body weight by Least Squares and DFREML in a Commercial Broiler Breeder Dam Population

To date commercial broiler breeders have focused primarily on increasing early growth rate in selection programmes aimed at improving overall production efficiency. In commercial programmes, early growth rate is simplified to a single body weight measure taken at a fixed age during the growth phase approaching common slaughter weights. Most recent selection studies report heritabilities from experimental populations that are at best, synthesised from crossing modern broiler material from several different sources (Leenstra et al, 1986; Wang et al, 1991). Therefore, such populations are likely to exhibit greater heterozygosity than many commercial lines which have undergone many generations of intense selection in closed populations. This paper reports heritabilities estimated using both least squares and derivative-free maximum likelihood techniques for data from a commercial breeder dam line which has remained closed since its inception in 1975.