近交与贴现对优化群体规模的影响

小群体的闭锁选育不可避免产生近交及遗传方差下降，导致近期与远期选择效果的矛盾。本文通过考察猪核心群育种方案中群体规模及公母比例对近交增量（％）及累积育种产出（元）的作用，分析遗传方差下降以及育种产出的贴现等因素对选择方案评估效果的影响。群体有效规模主要受每世代选择公猪头数的影响，为了控制群体近交增量必须维持一定的公猪头数。在所模拟的１６种方案中，１５代的贴现累积选择进展以每代选择８头公猪为最高；而母猪规模越大，累积选择进展越高。不考虑近交引起遗传方差的下降，或不进行选择进展的贴现，都造成过高估计选择方案的效果，且导致选择不适当的方案；对各世代选择进展进行贴现时，需要考虑较大的世代数，否则也会影响各选择方案的比较结果。

EFFECTS OF INBREEDING AND DISCOUNTING ON THE OPTIMUM POPULATION SIZE

Closed nucleus breeding in a small population inevitably result in inbreeding and decreasing of genetic variance. The present paper investigates the effects of population size on the inbreeding rate as well as accumulative genetic response. Meanwhile, the effects of considering the decreasing of genetic deviation and(or) discounting on the ranking of breeding schemes are analyzed.The effective population size mainly depends on the number of boars selected per generation. In order to control the inbreeding rate, it is necessary to maintain a highly number of boars per generation. For the alternative schemes, 8 boars selected per generation is optimum. The selection response increase with the number of sows.Disregarding the decreasing of genetic variance owing to selection and(or)discounting for selection response would result in overestimating of breeding schemes, and furthermore improperly selection of schemes. When the selection response is discounted, a high number of generation is needed, otherwise the errors may occur.