Gicheha M G, Kosgey I S, Bebe B O, Kahi A K
Animal Breeding and Genetics Group, Department of Animal Sciences, Egerton University, Njoro, Kenya.
J Anim Breed Genet. 2006 Aug;123(4):247-57. doi: 10.1111/j.1439-0388.2006.00598.x.
A deterministic approach was used to genetically and economically evaluate the efficiency of five two-tier nucleus breeding systems for meat sheep in Kenya. The nucleus breeding systems differed in terms of whether the system was closed or open, in the type of animals that were involved in the movement of genetic superiority and in the number of selection pathways in each system. These systems were compared under four alternative breeding objectives based on monetary genetic gain and profit per ewe. The first objective simulated a situation where the flock size cannot be increased due to non-feed related constraints (FLOCK). The second specifically assumed that the flock size is restricted due to limited amount of feed resources (FEED). The third and fourth objectives assumed that sheep performed only tangible roles (TR) and both tangible and intangible roles (IR) in the production system respectively. Monetary genetic gains were highest for all objectives in an open nucleus system with a certain proportion of commercial-born ewes being introduced in the nucleus while at the same time utilizing young rams from the nucleus to breed sires and dams for the nucleus and commercial sector (ONyre). Utilizing young rams in a closed nucleus system for the dissemination of superior genes resulted in higher annual monetary genetic gain than utilization of old rams. Profit per ewe was significantly higher for FLOCK and IR in ONyre. In a closed system that allowed for downward movement of dams from the nucleus to the commercial sector to breed sires and dams, profit per ewe was highest for FEED and TR. The success of a nucleus breeding system should also focus on the profitability and logistics of establishing it. The implication of these results on the choice of two-tier nucleus breeding systems for the improvement of meat sheep is discussed.
采用确定性方法，对肯尼亚肉用绵羊的五种两层核心育种系统的遗传和经济效率进行了评估。这些核心育种系统在系统是封闭还是开放、参与遗传优势传递的动物类型以及每个系统中的选择途径数量方面存在差异。基于货币遗传增益和每只母羊的利润，在四个替代育种目标下对这些系统进行了比较。第一个目标模拟了由于非饲料相关限制导致羊群规模无法增加的情况（FLOCK）。第二个目标具体假设由于饲料资源有限，羊群规模受到限制（FEED）。第三个和第四个目标分别假设绵羊在生产系统中仅发挥有形作用（TR）和同时发挥有形和无形作用（IR）。在一个开放核心系统中，所有目标的货币遗传增益最高，该系统中一定比例的商业出生母羊被引入核心群，同时利用核心群中的年轻公羊为核心群和商业部门培育种公羊和种母羊（ONyre）。在封闭核心系统中利用年轻公羊传播优良基因，比利用年老公羊获得的年度货币遗传增益更高。在ONyre系统中，FLOCK和IR目标下每只母羊的利润显著更高。在一个允许母羊从核心群向下转移到商业部门以培育种公羊和种母羊的封闭系统中，FEED和TR目标下每只母羊的利润最高。核心育种系统的成功还应关注建立该系统的盈利能力和后勤保障。讨论了这些结果对选择两层核心育种系统来改良肉用绵羊的意义。
