Ewe efficiency is extremely topical in the New Zealand sheep industry. This paper describes a stochastic simulation model which facilitates partitioning of a defined ewe efficiency equation into its component genetic traits. It accounts for, and simplifies, the complex and sometimes unfavorable interactions among components of ewe efficiency. The model tracks simulated genetic effects, inherited from the ewe's sires, in breeding ewes and their lambs for key performance recorded traits. The traits simulated are weaning weight, mature weight, number of lambs born, lamb survival, and longevity. Ewe efficiency is defined as the difference between value of lambs weaned and ewe and lamb costs, rather than as a ratio. Output value in NZ$ for the efficiency equation is computed on a ewe by ewe basis, as a function of number of lambs born, lamb survival and weight of lamb weaned, with each of these components partly influenced by one or more genetic effects inherited from simulated sires of the breeding ewes. Preliminary results from the model have identified litter size, ewe longevity, maternal lamb survival, and maternal weaning weight as being important drivers of ewe efficiency. The relative balance of their importance is influenced by farm production levels and environment.

JA, Sise, GH Shackell, TJ Byrne, SF Glennie, and PR Amer

Proceedings of the New Zealand Society of Animal Production, Volume 69, Christchurch, 223-227, 2009
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