奶牛育种中的长寿性状

A Review on Longevity Trait in Dairy Cattle Breeding

长寿性状是奶牛育种中最重要的功能性状之一,除产量性状之外,长寿性状具有最大的经济价值。由于遗传力低、数据分布特殊和性状表现晚等特点,长寿性状也是选育难度最大的性状之一。自上世纪50年代起,长寿性状就进入了各国奶牛育种家的视野,针对长寿性状的研究持续进行;上世纪90年代后,各奶业发达国家陆续将长寿性状纳入其奶牛综合选择指数。目前,我国奶牛综合选择指数(CPI)中尚不包含长寿性状,对长寿性状的研究也处于起步阶段。文章通过整理分析奶牛长寿性状的有关研究,从性状定义、遗传评估方法、与其他性状的关系、遗传标记、性状选育策略等方面系统介绍了长寿性状的研究和选育情况。通过汇总有关长寿性状与其他性状遗传相关的研究,阐述了长寿性状与其他性状之间的复杂关系;通过收集各国奶牛选育方案中的相关信息,重点介绍了各主要奶业发达国家对长寿性状的选育策略。此外,本文还通过收集在我国奶牛群体中针对长寿性状开展的研究,概述了奶牛长寿性状在我国的研究现状。长寿性状有许多不同的定义,可使用不同的模型对其进行遗传评估,包括线性模型、阈模型、生存分析模型和随机回归模型等。长寿性状与产量、体型、繁殖、健康和管理类性状等存在低到中等的遗传相关,线性体型性状中,与泌乳系统有关的体型性状与长寿性状的遗传相关较高;繁殖和健康性状表现更好的奶牛,其长寿性状通常表现更好;长寿性状与其他性状之间的遗传关系受牛群选育方向的影响较大,在不同群体中,长寿性状与同一性状的遗传相关不尽相同。奶业发达国家的奶牛综合选择指数中均包含长寿性状,这些国家除了使用直接长寿进行选择之外,部分国家还同时采用间接选择的方法对长寿性状进行选育,常用于间接选择长寿性的其他性状主要包括泌乳系统、腰强度、尻角度、肢蹄和乳房炎抗性等。在不同群体中,均发现了大量与长寿性状相关的遗传标记,其中大多数标记都定位在已报道的与繁殖、疾病和体型等性状相关的遗传区域内。文章还提出了从数据收集、遗传参数估计、遗传标记挖掘、评估模型和选择策略探讨等方面针对我国奶牛群体进行长寿性状研究的必要性。

Longevity is an important functional trait in dairy cattle. In addition to yield traits, longevity is more economically important than other traits in dairy breeding. The characteristics of longevity include low heritability, unfollowing normal distribution and performance later, hence longevity is the most difficult trait to select in dairy breeding. Since the 1950 s, dairy breeders have begun to pay attention to longevity traits. Now, researches on longevity traits have continued. After the 1990 s, longevity has been included in total selection index in many countries. However, longevity traits currently are not included in China Dairy Performance Index(CPI), and the study on longevity traits is also in its infancy in China. This review presented the trait definitions, methods of genetic evaluation, relationships between other traits, genetic makers, and selection strategies on longevity traits to systematically introduce its research and application in dairy industry. The complex relationships between longevity and other traits were described by summarizing the genetic correlation coefficients reported by many studies. The selection strategies for longevity traits in the various countries with developed dairy industry were highlighted by summarizing information collected from their dairy breeding program. Furthermore, this review also summarized the studies on longevity traits in dairy cattle in China. Longevity traits had various definitions, and there were various models used to preform genetic analysis, including linear model, threshold model, survival model and random regression model. There were low to moderate genetic correlations between longevity and other traits, including yield, linear type, fertility, health and workability traits, in which the higher genetic correlations were found between longevity and linear type traits in udder system. Generally, dairy cows with better performance on fertility and health traits were better on longevity. Among different populations, there were some differences on relationships between longevity and other traits, which were largely influenced by selection goals of current population. The total selection indexes in many countries included longevity. In addition to using direct longevity to select it, the indirect selection methods were also used in many countries. Udder system, strength, rump angle, feet and leg system, and mastitis resistance were comment traits used to indirect selection. Many genetic markers associated with longevity have been found in various populations, most of which were in genetic regions that have been reported to be associated with traits such as reproduction, disease and body type. Finally, this review also proposed the necessities of collecting longevity data, estimating genetic parameters, locating genetic markers, exploring evaluation model and selection strategy in China dairy cattle population.