GENETIC ANTAGONISM BETWEEN GROWTH AND MATERNAL ABILITY IN NELORE CATTLE

This study evaluated direct and maternal effects on 205 and 365 day we ights (W205 and W365) of 7415 Nelore calves, sired by 59 bulls and rai sed on pasture in the state of Sao Paulo, Brazil. Thirteen valiance an d covariance components for several different sets of related animals were estimated by least squares procedure and equated to their expecte d causal components. The system of equations gave estimates of heritab ility for direct effects (h(o)2) and for maternal effects (h(m)2). Est imates of h(o)2 were 0.26 for W205 and 0. 18 for W365. The estimates o f h(m)2 were 0.28 for W205 and 0. 18 for W365. The estimates of geneti c correlations between the direct and maternal effects (r(A)o(A)m) wer e -0.91 for both traits, suggesting a severe antagonism between the ef fects of genes for growth and genes for maternal ability. Estimates of total heritability (h(T)2) were only 10% of those obtained by the usu al paternal half-sib correlation.These results suggest that analyses t hat do not consider maternal effects in the Nelore breed overestimate genetic progress and long term response may be less than has been pred icted.