Authors: E D Ilatsia T K Muasya W B Muhuyi A K Kahi
Publish Date: 2006/12/20
Volume: 39, Issue: 1, Pages: 37-48
Abstract
Data comprising 7211 lactation records of 2894 cows were used to estimate genetic and phenotypic parameters for milk production lactation milk yield LMY and lactation length LL and fertility calving interval CI number of services per conception NSC and age at first calving AFC traits Genetic environmental and phenotypic trends were also estimated Variance components were estimated using univariate bivariate and trivariate animal models on based restricted maximum likelihood procedures Univariate models were used for each trait while bivariate models were used to estimate genetic and phenotypic correlations between milk production and fertility traits and between LMY LL CI and NSC within each lactation Trivariate models were used in the analysis of LMY LL CI and NSC in the first three lactations Heritability estimates from the univariate model were 016 007 003 004 and 001 for LMY LL CI AFC and NSC respectively The heritability estimates from trivariate analysis were higher for milk production traits than those from univariate analyses Genetic correlations were high and undesirable between milk production and fertility traits while phenotypic correlations were correspondingly low Genetic trends were close to zero for all traits while environmental and phenotypic trends fluctuated over the study period
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