摘要
The current interest in crossbreeding in the commercial dairy industry, even though it is quite limited, raises questions of breed utilization. Fewer than 5% of US dairy cattle are other than purebred or grade Holsteins. The large advantage of Holsteins for additive genetic merit for lactation milk yield is apparently responsible for this trend. Why, then, this interest in crossbreeding? The economic importance of traits such as reproduction, health, and survival in dairy production systems is likely the basis for the interest in crossbreeding, even though these traits are secondary to milk yield. Several US studies and a Canadian study confirmed that while several crossbred groups were equivalent to Holsteins for lactation milk yield, none were superior. Two crossbred groups in the Canadian study had lifetime yields, milk value, and net returns equivalent to Holsteins. In the New Zealand study, Friesian-Jersey reciprocal crossbreds were predicted to exceed Friesians in first-lactation fat yield. Crossbred performance is dictated by a combination of additive and nonadditive genetic effects. Evidence exists for direct, maternal, heterosis, and cytoplasmic maternal effects. Heterosis of 15 to 20% for lifetime traits was found in two studies. Results from previous crossbreeding studies have something to recommend for inclusion of Holstein, Ayrshire, Brown Swiss, and Jersey breeds in a crossbreeding scheme. However, multiple-generation lifetime performance on an array of purebreds and crossbreds under US condition does not exist. Full unique identification of individual animals, including breed composition, would permit the use of DHIA data to estimate additive and nonadditive genetic parameters for the traits recorded therein. Survival data from birth and health data would need to be fully recorded to provide complete data on lifetime performance. Self-propagation of crossbred replacements is mandatory if any crossbreeding system is to be successful. Based on current empirical data, a two-breed rotational crossing system appears to be the most viable system to maximize economic merit. The theoretical advantages of a three-breed rotational crossing system are clear, but the data to recommend the third breed and this system in practice are limited. Full-scale long-term breeding experiments or analysis of field data paired with a comprehensive modeling of alternative breed utilization strategies for US conditions are recommended.
摘要译文
目前对商业乳品行业的杂交育种的兴趣虽然很有限，但却引发了品种利用的问题。美国奶牛不到5％不是纯种或等级荷斯坦奶牛。荷尔斯泰因对哺乳期泌乳量的添加遗传价值的巨大优势显然是造成这一趋势的原因。那么，为什么这种兴趣在杂交？奶牛生产系统中繁殖，健康和生存等特征的经济重要性可能是杂交育种的基础，即使这些特征是产奶量的次要因素。美国的几项研究和加拿大的一项研究证实，尽管几种杂交组与泌乳牛奶产量相当，没有优势。加拿大研究中的两个杂种群体的终身收益率，牛奶价值和相当于荷尔斯泰因的净收益。在新西兰的研究中，预计Friesian-Jersey互惠杂交种在第一次泌乳期的脂肪产量方面超过Friesians。杂种表现由加性和非加性遗传效应的组合决定。存在直接，母体，杂种优势和胞质母体效应的证据。两项研究发现终生性状的杂种优势为15％至20％。以前的杂交育种研究的结果有一些建议将荷斯坦，艾尔郡，布朗瑞士和泽西品种纳入杂交育种计划。然而，在美国条件下的纯种和杂交种阵列上的多代生命期表现不存在。对个别动物的完全独特识别，包括品种组成，将允许使用DHIA数据来估计其中记录的性状的加性和非加性遗传参数。需要完整记录出生和健康数据的生存数据，以提供有关终生表现的完整数据。如果任何杂交育种系统成功，则杂交替代品的自繁殖是强制性的。根据目前的经验数据，一个双品种的旋转交叉系统似乎是最大化经济价值的最可行的系统。三品种旋转交叉系统的理论优势很明显，但在实践中推荐第三品种和该系统的数据是有限的。建议进行全面的长期繁殖实验或现场数据分析，并对美国条件下的替代品种利用策略进行全面建模。
A.J.McAllister;. Is Crossbreeding the Answer to Questions of Dairy Breed Utilization?1[J]. Journal of Dairy Science, 2002,85(9): 2352-2357