Dekkers J C
Department of Animal and Poultry Science, University of Guelph, ON, Canada.
J Dairy Sci. 1994 Nov;77(11):3441-53. doi: 10.3168/jds.S0022-0302(94)77287-8.
Calving ease is of economic importance in dairy cattle and should be considered in breeding programs. Economic values of direct and maternal calving ease were derived based on cost-benefit analysis and gene flow methodology. Marginal returns from dystocia reduction in primiparous dams were -$43 per phenotypic standard deviation compared with $300 for production. For an average mate, numbers of discounted expressions for sires to breed replacements were .58, .44, and .63 for direct and maternal calving ease and production. Discounted expressions for direct calving ease were higher when sires were mated to primiparous versus multiparous dams. Three alternative breeding strategies were compared: 1) separate selection of sires as mates of primiparous and multiparous cows, based on their respective optimal indexes for direct and maternal calving ease, 2) selection based on the optimal index for an average mate, and 3) selection on direct calving ease only. Strategies 2 and 3 allowed for assortative mating of sires with favorable direct calving ease to primiparous females subsequent to selection. Strategy 2 resulted in maximal economic response. Optimal standardized index weights under Canadian circumstances were approximately 100:9:7 for production:direct calving ease:maternal calving ease. Inclusion of calving ease traits had a minor effect (< .5%) on selection responses and efficiency but would provide proper guidelines to producers. Greatest benefits of genetic evaluations for calving ease were obtained through assortative mating.
产犊难易度在奶牛养殖中具有经济重要性，应在育种计划中予以考虑。基于成本效益分析和基因流方法得出了直接产犊难易度和母系产犊难易度的经济价值。初产母牛难产减少带来的边际收益为每表型标准差 -43 美元，而生产性状的边际收益为 300 美元。对于平均配偶，种公牛繁殖后备母牛的直接产犊难易度、母系产犊难易度和生产性状的贴现表达数量分别为 0.58、0.44 和 0.63。当种公牛与初产母牛而非经产母牛交配时，直接产犊难易度的贴现表达更高。比较了三种替代育种策略：1）根据初产母牛和经产母牛各自的直接产犊难易度和母系产犊难易度最优指数分别选择种公牛作为配偶；2）根据平均配偶的最优指数进行选择；3）仅根据直接产犊难易度进行选择。策略 2 和 3 允许在选择后将具有有利直接产犊难易度的种公牛与初产母牛进行选型交配。策略 2 产生了最大的经济响应。在加拿大的情况下，生产性状、直接产犊难易度、母系产犊难易度的最优标准化指数权重约为 100:9:7。纳入产犊难易度性状对选择反应和效率的影响较小（<0.5%），但可为生产者提供适当的指导。通过选型交配可获得产犊难易度遗传评估的最大益处。
