Genetic correlations between longevity and conformation traits in an upgrading dairy cattle population.

Genetic correlations between longevity and conformation traits were estimated 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 equivalents (i.e., the longevity traits corrected for production). For the 1989 plus 1990 data file, only stayabilities until 36 and 48 mo of age were considered. Conformation traits were rear legs set, front teat placement, udder depth, suspensory ligament, and subjective scores for udder, feet and legs, and type. Also investigated was a possible nonlinear relationship between conformation and longevity traits. Genetic correlations between conformation and longevity traits differed between years of birth, mainly because farmers practiced large-scale upgrading with Holstein-Friesian bulls during the period considered, which caused a change in desired type. Therefore, the predictive value of conformation traits for longevity based on data from an upgrading population, might be limited. Estimates of genetic parameters should be based on the most recent data possible, and these parameters should be reestimated over time. From the 1989 plus 1990 data file, subjective scores for udder and feet and legs had the highest predictive values for functional longevity. Quadratic relationships between conformation and longevity traits did exist, but generally the linear relationships prevailed.