Genetic parameters for weaning weight of Kenyan Boran cattle accounting for direct-maternal genetic covariances
CB Wasike, ED Ilatsia, J MK Ojango, AK Kahi
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Genetic parameters were estimated for weaning weight (WW) in Kenya Boran cattle using animal models that assumed non-zero direct-maternal genetic covariance. In addition to the direct and maternal genetic effects, maternal permanent environmental and sire by herd-year interaction effects were tested. Two datasets were used. Dataset 1 (DS1) included all animals while dataset 2 (DS2) constituted only records of animals with known paternity. Estimates of direct and maternal heritabilities from DS1 ranged from 0.61 to 0.64 and 0.25 to 0.27, respectively. Estimates of direct and maternal heritabilities from DS2 ranged from 0.07 to 0.31 and 0.16 to 0.23. Direct-maternal genetic correlations were large and negative but were lower in the analyses of DS2 than in DS1. Similarly, estimates of direct and maternal heritability were lower in the analyses of DS2 than in DS1 especially when the effect of sire by herd-year effect was fitted in the model. This study shows that WW is highly heritable and under the influence of maternal effects. Estimates of genetic parameters and direct-maternal genetic covariance are dependent on data size and structure and how direct and maternal effects have been accounted for.