Impact of conformation traits on genetic evaluation of length of productive life of holstein cattle

摘要

Length of productive life is an important economic trait in dairy cattle that has shown to have a genetic component and thus, it is subject to improvement through selection. Lifetime records of 13,659 Holstein cows from 72 herds, calving for the first time between January 2000 and December 2014 and their conformation, milk yield (ME 305 d milk) and pedigree information were used to evaluate the relationship of conformation and length of productive life. Length of productive life was adjusted to a maximum of 305 days for each lactation and of these 34% were right censored records. The objective of this study was to investigate the effect of conformation traits on the genetic evaluation of functional length of productive life of Mexican Holstein cattle using survival analysis with a sire-maternal grandsire model. The hazard function was modeled with a baseline function assumed to follow a Weibull distribution, including the fixed covariates of age at first calving and conformation traits (one at a time), time dependent covariates (random effect of herd-year of calving, milk yield level, and lactation phase with changes at 29, 249 and 305 days in each of the first four lactations), and random effects of sire and maternal grandsire. All effects incorporated in the model, before including conformation traits had significant contributions to the likelihood function (P <0.05), and when conformation traits were included, five of them (chest width, teat length, median suspensory ligament, udder texture and udder depth) were statistically significant in order to predict breeding values for length of productive life; therefore the genetic evaluation for length of productive life should include these traits as indirect predictors of longevity. This study strongly recommends the inclusion of conformation traits in the model for genetic improvement of length of productive life of Mexican Holstein cattle.