Genetic parameter estimates for functional herd life for the South African Jersey breed using a multiple trait linear model (Short Communication)
Longevity reflects the ability of a cow to avoid being culled for low production, low fertility or illness. Longevity can be used in breeding programmes if genetic parameters are known. Various measures are used for longevity. In this study survival in each of the first three lactations was analysed. Survival was denoted by a 1 if a cow survived, and 0 otherwise. The primary objective of the current study was to estimate genetic parameters for functional herd life. The secondary objective was to compare estimates of genetic parameters from the linear sire and animal models. Data and pedigree records on purebred Jersey cows that participated in National Milk Recording and Improvement Scheme of South Africa were used to estimate genetic parameters. A total of 181 269 cow records from 636 herds recorded over 16 years were available for analysis. Estimates of genetic parameters for herd life were obtained using REML procedures fitting three-trait (first three lactations as separate traits) linear animal and sire models. Heritability estimates (0.02 to 0.03) from the animal and sire models were somewhat similar for all lactations. However, heritability estimates for lactations 2 and 3 were slightly higher with the sire model compared to the animal model. The genetic correlation between lactations 1 and 2 from both the sire and animal models was higher than that between lactations 2 and 3. Genetic correlations from the sire model ranged from 0.68 to 0.99, compared to 0.76 to 0.99 from the animal model. Results from the current study suggest that genetic variation exists for functional herd life to allow for genetic improvement through selection. The moderate positive genetic correlation between survival in the first and third lactation suggest that early selection for functional herd life is feasible.