Estimated Genetic Improvement in Weaning Weight of Beef Cattle

Individual and Maternal Additive and Heterotic Effects on 205-Day Weight in Beef Cattle

“…Currently, genetic methods to increase weaning weight involve the choice of replacement animals. The low to moderate heritability of weaning weight (Preston and Willis, 1974;Woldehawariat et al, 1977), low reproductive rate of cattle, long generation interval and the relatively low selection differentials make traditional intrabreed phenotypic selection for higher weaning weights a slow and tedious method of improvement (Chapman et al, 1969;Koch et al, 1974;Nwakalor et al 1976). A more viable option may be to choose among breeds in a way that permits utilization of breed differences in individual and maternal additive effects and heterosis to increase weaning weight.…”

Selection for Increased Weaning or Yearling Weight in Hereford Cattle. II. Direct and Correlated Responses2

“…54 kg/yr for BW and WW in inbred Hereford lines selected for increased growth. Nwalakor et al (1976) also selected for growth in inbred Buchanan et al (1982), also in Hereford lines, reported similar genetic responses/generation for WW (.24 and .25 o in WWL and YWL) but higher responses for YW (.29 and .39 o in WWL and YWL), where genetic responses were predicted from paternal half-fib and parent-offspring regression estimates of genetic parameters in the lines and selection indexes calculated in retrospect. Brinks et al (1965), selecting on an index of several traits in Hereford lines, reported more rapid genetic changes/generation for WW (.33 o) and postweaning growth (.38 o in off test weight for bulls and .40 e for 18-too weight in heifers).…”

Selection in Hereford Cattle. II. Expected and Realized Response

“…Genetic change amounted essentially to zero for HGC at birth and showed a slight decrease of -.024 points for WS during the selection period. About equal phenotypic and genetic changes of .432 and .423 kg/yr in WW would imply that the environment was fairly stable so that virtually all the phenotypic improvement was genetic; the results obtained for the inbreds and those from previous study (Nwakalor et al, 1976) make this seem unlikely.…”

“…The line culling provided opportunity to enlarge more promising lines and start new ones and also should lead to faster genetic progress in the overall herd. Previous analysis of data demonstrated that the discontinued lines had, in fact, below-average genetic merit (Nwakalor et al, 1976).…”

“…Received April 1, 1985. Accepted October 30, 1985 can be a potent means of changing the population means (Flower et al, 1963;Harwin, 1963;Brinks et al, 1967Brinks et al, , 1971Brinks et al, , 1972Urick et al, 1968;Ray et aI., 1970;Lasley, 1972;Nwakalor et al, 1976).…”