Genetic parameters for milk yield of Bubalus bubalis using unadjusted and adjusted milk production for days in milk.

Abstract

The objectives of this study were to estimate genetic parameters for unadjusted and adjusted milk production for 270 and 305 days of lactation and, subsequently, to verify the coincidence of rank of 2%, 5%, 20% and 40% best sires selected based on both models. Complete lactations from 90 or 150 days of lactation to 270 or 350 days of lactation were considered in the analyses. Milk production was adjusted for lactation length by multiplicative correction factors, or by including lactation length as a covariable in the model. Heritabilities, genetic correlations and breeding values were estimated for each trait, and variance and covariance components were estimated by restricted maximum likelihood methodology. Heritability estimates varied from 0.16 to 0.27. Genetic correlations between unadjusted and adjusted milk production for lactation length were higher than 0.64. Heritabilities for adjusted milk production were higher than heritabilities for unadjusted milk production for lactation length. In situations with high selection intensity, probably, modifications will happen in the rank of bulls and/or in the bulls chosen for mating if records are adjusted or unadjusted for 305 days.