中国荷斯坦牛优化繁育体系研究

本文论述了目前各国使用的三种奶牛繁育体系（待定公牛体系、精液长期保存体系、青年公牛体系）的优缺点，结合我国特别是北京市现行育种方案，比较了不同繁育体系的育种成效，根据我国目前的生产条件和价格体系，提出了对我国现行奶牛繁育体系的优化方案。

Studies on the optimization of breeding programs for Chinese Hostein Cattle

The currently proceeded breeding system in Chinese Hostein cattle (CS)was analyzed and compared with the three world wide commonly used breeding systems, waiting bull system(WB), semen storage system(SS), and yang bull system(YB), in terms of genetic progresses and breeding benefit by using gene now method and model calculations. Traits considered are fat yield, daily gain, carcass quality, growth capacity, mating interval, stayability, and somatic dell score. The results shows that for the current population structure and production and market conditions, the SS system would give the greatest aggregated genetic progress while the YB system would give the greatest aggregated genetic progress while the YB system give the largest breeding benefit. The CS system, which is a mixture of WB and YB system but much closer to YB, is slightly better than WB system in both aspects. However, the differences among the sour systems are generally small and it seems that it is not necessary to change the currently used breeding system in China. Although the current sysetem is acceptable, it still needs to find an optimized breeding plan under this system with respect to population and breeding structure to make greatest genetic progress and breeding benefit. Following factors are considered in the optindzation: population size, number of bulls to be progeny tested each year, proportion of cows to be used for progeny testing. The results from a lot of model calculations show that with population size changing from 30, 000, 60, 000, 120, 000, to 240, 000, and with a proportion of active breeding cows being 50%, the optimal proportion of cows to be used for progeny testing is 50% to 70%, and the optimal number of bulls to be progeny tested each year is 20, 30, 50, and 70, respectively. The corresponding breeding benefit increases from 155. 45, 178. 47, 199. 22, to 217. 63(Yuan) and the aggregated genetic progress increases from 20.66, 23. 00,25.24,to 27. 39(Yuan), respectively. At present, the dairy cattle breeding in different provinces and cities in China is basically independent of each other and the present population size in each province or city is generally small, for example, only about 30, 000 cows in Beijing area. One way to increase population size is to join the neighbored provinces or cities together, which can be realized greatly by selecting and utilizing common bulls across provinces or cities. Moreover, in each province or city, only about 25% of active breeding cows participate progeny testing programs and only 5 - 10 young bulls are progeny tested each year. This situation needs to be changed very urgently according to this study.