Syrstad O, Ruane J
Centre for International Environment and Development Studies, Agricultural University of Norway, As, Norway.
Trop Anim Health Prod. 1998 Aug;30(4):257-68. doi: 10.1023/a:1005083430140.
The import of genetic material and the use of crossbreeding to improve the dairy merit of tropical cattle has been criticized for eroding the livestock genetic resources of the tropics. An alternative is genetic improvement of the indigenous cattle through selection. The objective of the present paper is to examine the feasibility of this alternative. Constraints to genetic improvement of tropical cattle through selection are discussed. Low reproductive rates and high calf mortality reduce the intensity of selection. The generation interval, which is long in cattle, is further prolonged by the late sexual maturity and the long calving intervals in most tropical breeds. The most serious constraint is, however, that the extensive milk recording schemes which support dairy cattle breeding programmes in many temperate countries are almost non-existent in the tropics. In this situation, the most realistic approach to improvement through selection is to start with a single nucleus herd (or a group of cooperating herds). Two alternative selection programmes (with and without progeny testing) for a closed herd of 500 cows are outlined. The alternative which assumed no progeny testing, i.e. selection of bulls on pedigree information only, gave the fastest genetic improvement (predicted at 36 kg/year). By distributing breeding bulls from the herd the genetic progress can be disseminated to the outside population with a time lag of about two generations. A nucleus herd can supply about 15 selected bulls per 100 cows in the herd per year, enough for a population of several thousand cows.
引进遗传物质以及利用杂交来提高热带牛的产奶性能，因侵蚀热带地区的家畜遗传资源而受到批评。另一种方法是通过选育来改良本地牛的基因。本文的目的是研究这种替代方法的可行性。文中讨论了通过选育来改良热带牛基因所面临的限制因素。低繁殖率和高犊牛死亡率降低了选育强度。牛的世代间隔本来就长，而大多数热带品种的性成熟晚和产犊间隔长，进一步延长了世代间隔。然而，最严重的限制因素是，许多温带国家支持奶牛育种计划的广泛的产奶记录方案在热带地区几乎不存在。在这种情况下，通过选育进行改良的最现实方法是从单个核心牛群（或一组合作牛群）开始。文中概述了针对一个500头母牛的封闭牛群的两种替代选育方案（有后代测试和无后代测试）。假设无后代测试的方案，即仅根据系谱信息选择公牛，能实现最快的基因改良（预计为每年36千克）。通过从该牛群分发种公牛，基因进展可以在大约两代的时间滞后传播到外部群体。一个核心牛群每年每100头母牛可以提供约15头经过挑选的公牛，足以满足几千头母牛群体的需求。
