Genetic, Environmental and Interaction Effects in Sheep I. Reproduction and Lamb Production per Ewe

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Abstract
Genetic, environmental and interaction effects on ewe reproduction and productivity are reported from a diallel cross among three breeds replicated over 3 years and two grazing management systems. Breeds were the Hampshire, Suffolk and Willamette (a strain with Columbia, Dorset Horn and Border Cheviot ancestry). Management systems were improved dryland hill pastures vs irrigated and heavily fertilized lowland pastures. Hill pasture management resulted in lower prolificacy but greater lamb survival to weaning and more kilograms of lamb weaned per ewe lambing and per ewe joined. Differences among sires accounted for 22% of the variation in ewe fertility. There were no important sire breed differences or sire breed × management system or year interactions. Dam breed × management interactions involving changes in rank were found for ewe fertility and productivity. Averaged across environments, heterosis for fertility, prolificacy, survival and production per ewe lambing and production per ewe bred, respectively, were 5.7%, 1.8% (not significant), 3.2% (not significant), 8.6% and 13.5%. There was a tendency for greater heterosis for ewe productivity from crosses among the breeds less similar genetically. Also heterosis for productivity appeared to be limited when the dam breed in the cross had poor maternal potential. For total ewe production, there was an important mating system × environment interaction. On irrigated pastures which resulted in less production per ewe, heterosis was 30.1%, whereas on hill pastures heterosis was only 1.4%. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.

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