Genotype x environment interactions in sheep Public Deposited

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  • The 865 ewe production records taken from three lamb crops, were analyzed to study breed effects, heterosis, environmental effects and interactions between them, and breed and heterosis x environment interaction effects on ewe production traits. In each of two environments, approximately 144 ewes were mated in a three breed reciprocal cross design each year. The resulting 757 parturitions produced 1263 lambs. Hampshire, Suffolk and Willamette sheep from university flocks were used. Two rams of each breed were used in each environment each year. One location was rolling hill land, the other was level, irrigated, valley bottom land, both near Corvallis, Oregon. Least squares analyses of variance were computed on ewe production traits which included fertility, lambs born, percent survival to weaning, lambs weaned and pounds of lamb weaned. None of the effects tested in the analysis of fertility showed significance. On the other traits, year was significant except for survival. Location was significant for pounds weaned per ewe mated and for lambs born, percent weaned and pounds weaned per ewe lambing. The main effect of the hill land was superior except for lambs born per ewe which lambed. Dam age was significant except for survival. The age effect on fertility was not tested. Otherwise production increased with age. Dam weight change during the mating season was significant for pounds weaned per ewe mated and for prolificacy. Pounds weaned increased with weight gain while prolificacy decreased. Lambing date was significant for lambs born and lambs weaned per ewe lambing. Prolificacy increased as the lambing season progressed. Location x year interaction effects on pounds of lamb weaned per ewe mated and on lambs weaned, percent weaned and pounds of lamb weaned per ewe which lambed were significant. Dam breed and dam x location interaction were significant for pounds weaned per ewe mated. The overall and hill land ranking of ewe breeds was Willamette, Suffolk, then Hampshire. The interaction re. sulted primarily from a disproportionate increase in the performance of the Willamette ewes on the hill land. The Suffolk ewes were superior on the irrigated pasture. This suggests that a superior adaptation of Willamette ewes to hill land has resulted during their development and selection there. Sire x year was significant for lambs born. The interaction effect alone, however, in no case was more than 0.10 lamb so its importance is questionable. Heterosis and heterosis x location interaction were significant for pounds weaned per ewe mated. Heterosis was 31.3% for pounds weaned per ewe mated on the valley pasture and 8.2% on the hill pasture. These results suggest that heterosis is greater when conditions for the expression of a given trait are suboptimal.
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