Nugent R A, Jenkins T G
Roman L. Hruska U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NE 68933-0166.
J Anim Sci. 1993 Feb;71(2):310-20. doi: 10.2527/1993.712310x.
A deterministic computer simulation model was used to estimate the effects of different culling strategies for nonconception and age on the biological efficiency of an annual lambing system. Interaction among culling strategy and genotype for system efficiency was estimated by also varying ewe genetic potentials for fertility, precocity of fertility, and litter size. Biological efficiency was defined as grams of empty body weight equivalent value of market lamb, cull ewe, and wool output per kilogram input of TDN. Pure breeding with random selection of intraflock replacement ewe lambs was assumed. Sheep were fed to maintain normal weight. Maximum allowable ewe age (i.e., time at culling for age) was varied from 2 to 10 yr. The four strategies of culling for nonconception that were simulated ranged from no removal for nonconception to removal of all nonpregnant ewes 15 wk after exposure. During calculation of lamb empty body weight equivalent, relative values per kilogram of output for market lambs, cull ewes, and clean wool were assumed to be 1 to .33 to 2.04 for most simulation runs. In addition, relative value of cull ewes was varied to .01, .16, .50, or .99 for some simulations. The effect of strategy for removal of nonconceiving ewes on system efficiency depended on maximum ewe age and genotype. In general, if relative value per kilogram of cull ewes to market lambs was < or = .50, ewes should be allowed to produce through 4 or 5 yr of age and then be salvaged. Unless salvage value of culled ewes approaches that of market lambs, ewe lambs should not be culled for failure to conceive.
使用确定性计算机模拟模型来估计不同的非受孕和年龄淘汰策略对一年生羔羊系统生物效率的影响。通过改变母羊在繁殖力、繁殖早熟性和产羔数方面的遗传潜力，还估计了淘汰策略与系统效率基因型之间的相互作用。生物效率定义为每千克可消化总养分（TDN）投入所产生的市场羔羊、淘汰母羊和羊毛产量的空体重当量值（以克为单位）。假设采用随机选择群内替代母羊羔进行纯种繁育。给绵羊喂食以维持正常体重。最大允许母羊年龄（即因年龄而淘汰的时间）从2岁到10岁不等。模拟的四种非受孕淘汰策略范围从不对非受孕母羊进行淘汰到在配种后15周淘汰所有未怀孕母羊。在计算羔羊空体重当量时，对于大多数模拟运行，市场羔羊、淘汰母羊和净毛每千克产出的相对值假定为1比0.33比2.04。此外，在一些模拟中，淘汰母羊的相对值分别变为0.01、0.16、0.50或0.99。淘汰未受孕母羊的策略对系统效率的影响取决于最大母羊年龄和基因型。一般来说，如果每千克淘汰母羊相对于市场羔羊的相对值≤0.50，则应允许母羊产仔至4或5岁，然后进行淘汰。除非淘汰母羊的残值接近市场羔羊的残值，否则不应因未受孕而淘汰母羊羔。
