The literature on seasonality of breeding and prolificacy in sheep and goats is reviewed. The evidence in relation to genetic variation within and between breeds is most substantial in the case of prolificacy in sheep; showing large and essentially additive differences among breeds and considerable genetic variation within breeds including genes with a large effect on ovulation rate in at least three very different populations. The literature on goats is much less extensive. Information on the genetic architecture of breed differences in breeding season length is very limited in both species and substantial information on within breed genetic variation is largely confined to data relating to the onset of the breeding season in sheep. The available information for sheep suggests that breeding season length has a low to moderate heritability and is positively related to prolificacy. It is suggested that increased annual reproductive rate is readily obtained by exploiting breed differences in ovulation rate or utilising single gene effects. Increasing the number of pregnancies per annum should be pursued by selecting directly for length of the breeding season in an index with ovulation rate.

J. P Hanrahan, J. F Quirke

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XI. Genetics of reproduction, lactation, growth, adaptation, disease, and parasite resistance., , 30–45, 1986
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