Genetic parameter estimates and cluster analysis of breeding values for milk production in Guzerá cattle

Abstract Text: The aim of this study was to explore the genetic curve pattern of EBVs for test-day milk yield of Guzerá cattle using cluster analysis. Test-day milk yields of 5,274 first-lactation Guzerá cows were recorded in a progeny test from 1987 to 2012. A total of 34,193 monthly records were analyzed with a random regression animal model using Legendre polynomials to fit additive genetic and permanent environmental random effects and the mean trend. Residual variances were modeled by a step function. Hierarchical and non-hierarchical cluster analyses were performed based on the EBVs for monthly test-day milk yield, peak yield, lactation persistency, and partial cumulative and 305-day yields. The heritability estimates for test-day milk yields ranged from 0.24 to 0.52. Cluster analysis identified animals in the population that belong to different groups according to milk production level and lactation persistency.

Keywords:

lactation curve

persistency

random regression

Zebu cows