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Some Aspects of Twin versus Single Lambs of Navajo and Navajo Crossbred Ewes

United States Department of Agriculture¹

Abstract

The advantage in weight of lambs produced by ewes having twins compared to ewes having singles, weaning weight of single and twin lambs, survival rates of single and twin lambs and heritability of type of birth was investigated for Navajo and Navajo crossbred ewes.

The difference in weight of lambs weaned per ewe between the two breeds studied was not significant. However, the difference in weight of lambs per ewe between ewes having singles, and ewes having twins, was highly significant. The interaction between Navajo versus crossbred times year was not significant, indicating the Navajo ewes do not withstand severe drought conditions any better than do the crossbred ewes. On a per lamb basis, the difference in weight of lambs weaned is significantly greater for crossbreds than for Navajo ewes. A significant difference was found in survival rates for crossbred single and twin lambs. This was not true for Navajo single and twin lambs, A higher death rate was observed in the crossbred twin lambs than in the Navajo twin lambs. The Navajo ewes show a 10 percent advantage in the number of ewes having twins. The heritability of twinning was found to be 22 and 12 percent, respectively, for mature crossbred and Navajo ewes.

¹ Southwestern Range and Sheep Breeding Laboratory, Fort Wingate, New Mexico, in cooperation with the New Mexico State College, and the Bureau of Indian Affairs, Washington, D. C.