Crossbreeding programmes of different complexity are formulated and used in various parts of the world with the objective to improve the biological efficiency of livestockproduction. A central theme of the crossbreeding strategy is the utilisation of heterosis (or hybrid vigour) which, as a measure of the superiority in performance_of the Fj_ crossbreds over the comparable purebreds, may originate from the sire, the dam and/or the progeny. There is evidence (Nitter, 1978) to suggest that different sources of heterosis U) i.e. paternal (h?), maternal (hM), and individual (hi), are involved in the superior lamb production performance observed to occur usually with crossbreeding. No published data, however, appear to be available on the comparative magnitude of these 3 sources of heterosis, or between each of them and the recombination effect (rl, Dickerson, 1969) which may also be present in a crossbreeding programme for lamb production.

In Phase III of the CSIRO sheep crossbreeding experiment, a 3-year project (1979-1981/82) was undertaken to evaluate five heterosis utilisation breeding policies (Ch ang and Atkins, 1981) in terms of 'total weight of lambs weaned per ewe joined' in a 3-breed (Dorset Horn, Merino, Corriedale) population. The purpose of this paper is to present the main results from the project with special reference to the comparative estimates of h*, h^, hi, and their utilisation in formulating a breeding policy to maximise lamb production per ewe joined.

T. S Ch'ang, R Evans

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 8. Symposia (2), , 796-801, 1982
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