GENETIC CORRELATIONS BETWEEN LONGEVITY AND CONFORMATION TRAITS IN AN UPGRADING DAIRY-CATTLE POPULATION

Genetic correlations between longevity and conformation traits were es timated using data on Dutch Black and White cows born in 1978 (11,558 records), 1982 (39,252 records), and 1989 plus 1990 (58,864 records). Longevity traits considered were number of lactations, herd life, and stayabilities until 36 and 48 mo of age and their functional equivalen ts (i.e., the longevity traits corrected for production). For the 1989 plus 1990 data file, only stayabilities until 36 and 48 mo of age wer e considered. Conformation traits were rear legs set, front teat place ment, udder depth, suspensory ligament, and subjective scores for udde r, feet and legs, and type. Also investigated was a possible nonlinear relationship between conformation and longevity traits. Genetic corre lations between conformation and longevity traits differed between yea rs of birth, mainly because farmers practiced large-scale upgrading wi th Holstein-Friesian bulls during the period considered, which caused a change in desired type. Therefore, the predictive value of conformat ion traits for longevity based on data from an upgrading population, m ight be Limited. Estimates of genetic parameters should be based on th e most recent data possible, and these parameters should be reestimate d over time. From the 1989 plus 1990 data file, subjective scores for udder and feet and legs had the highest predictive values for function al longevity. Quadratic relationships between conformation and longevi ty traits did exist, but generally the linear relationships prevailed.