Selection for the direct and maternal genetic effects for dystocia in Holsteins

The effects of selection for the direct and maternal components of dystocia were estimated for first, second and later, and all parities. The effect of restricting maternal change to zero and the effect of selection for only the direct component were also examined. Gene flow procedure was used to compute economic weights as 1 and .347 for the direct and maternal effects, respectively. Genetic gain in aggregate genotype was the largest for first parity. For all parities all the gain in the aggregate genotype was accounted for by the direct effects. At the same time, a slight decrease in the genetic maternal effects was observed. For all cases, selection for both traits had almost no loss in aggregate genotype or accuracy compared with when maternal changes were restricted to zero. Total genetic gain and genetic gain for the direct effect of dystocia were greater and accuracy of selection was lower when selection was for the genetic direct effect only versus the index that included both direct and maternal effects. Selection for only the direct effects is not likely to produce any significant change in dystocia as a maternal trait.