Parámetros genéticos y factores ambientales asociados al peso vivo en vacas lecheras

Live weight (LW) in dairy animals is a trait of strategic relevance in production systems, as it influences both farm income and costs. On the one hand, it relates to productive potential and feed efficiency; on the other, it determines maintenance requirements and conditions animal longevity and health. A detailed understanding of the magnitude of the genetic and environmental variation of LW, as well as its associated parameters, is essential for its inclusion in genetic selection and improvement programs.

The present study aimed to estimate the genetic parameters of LW in dairy cows, using productive and genealogical data processed via Bayesian mixed models implemented in the thrgibbs1f90 program from the BLUPF90 package. For this purpose, 1844 LW records corresponding to 1610 Holstein cows, with productive and genealogical information, were analyzed. The analysis was conducted using a univariate repeated measures model that included fixed effects of contemporary group (combination of herd and weighing date), lactation–age combination, and stage of lactation; and random effects of animal (additive genetic effect), permanent environmental effect, and residual error.

The model outputs allowed for the estimation of additive genetic variance (VA), permanent environmental variance (VEP), and residual variance (VR). From these, total phenotypic variance (VP), heritability (h²), and repeatability (r) were calculated for each posterior sample generated by Gibbs sampling, also obtaining the means and 90% credibility intervals (5th and 95th percentiles) for each parameter.

The results indicated that LW presented an average heritability of 0.593 (90% CI: 0.473 – 0.692) and an average repeatability of 0.778 (90% CI: 0.731 – 0.817). These values reflect that a large part of the phenotypic variation in LW is due to additive genetic variation, and that measurements are consistent for the same animal over time. Likewise, it was observed that the environmental effects included in the model had a significant influence on LW, particularly the contemporary group, lactation–age, and stage of lactation.

Overall, these results suggest that LW is a highly heritable and repeatable trait, with high potential for response to genetic selection. Its inclusion in breeding programs, along with the control of the identified environmental effects, could contribute to optimizing productive and economic efficiency in dairy systems, favoring the sustainability and competitiveness of the activity.