Heterogeneity of variance for lactation persistency and milk yield at 305 days of Gir cows in different environments

Abstract Text: The objective of this study was to evaluate the heterogeneity of variance for lactation persistency and milk yield at 305 d (MRA 305) according to different production environments. Records from 38,220 test day milk yield of Gir cows were analyzed. Environments were discriminated in high and low production using k-means clustering. In genetic analysis was used a two-trait random regression model, by Legendre polynomials. Covariance components were obtained by Bayesian inference. To verify the behavior of persistence in different production environments were employed 12 measures (PSi). K-means provided significant differences between environmental groups. Generally, both estimates of heritability and genetic correlation for different measures of persistence and MRA305 showed differences in the two environmental groups. Results showed that in groups of low production, PS2 and PS10 could be considered in genetic evaluations for increased production in the first lactation of Gir cattle.

Keywords:

Genetic evaluation

Random regression

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