|Abstract or Summary
- 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.