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Ovulation Rate and Litter Size of Barbados, Targhee and Crossbred Ewes¹

University of California^,3, Davis 95616

Abstract

Ovulation rate was measured in Barbados Blackbelly (United States strain; B), Targhee (T), Barbados x Targhee (B x T) and Barbados x Dorset-Targhee (B x DT) ewes at first and second estrus following synchronization of cycles early in the breeding season. Body weight at sponge removal differed (P<.001) between B (30.9 kg) and T ewes (54.9 kg) and was intermediate for B x T (44.9 kg) and B x DT (43.5 kg) ewes. Ovulation rate was higher (P<.01) at first and second estrus for B (1.86, 2.04), B x T (1.93, 2.04) and B x DT (1.72, 1.80) than for T (1.29, 1.40) ewes. Regressions of ovulation rate on body weight within the breed groups did not differ significantly from each other and the average was significant (b = .049 ± .014 CL/kg at first estrus and b = .046 ± .011 CL/kg at second estrus, where CL = number of corpora lutea), but differences between the groups in body weight did not explain the differences in ovulation rate. Litter size for B, B x T, B x DT and T groups was 1.71, 1.84, 1.84 and 1.28, respectively. The B x T ewes were superior to the average of the B and T ewes for ovulation rate (P<.05) and litter size (P<.01); there was no direct estimate of embryo survival, but the results indirectly indicate superiority of the crossbreds for this component also. The B, B x T and B x DT ewes were all exceptionally uniform in ovulation rate and litter size; 81 and 69% of the CL counts for B and B crossbred ewes, respectively, were two, and 68 and 79% of the litters produced by B and B crossbred ewes, respectively, were twins.

¹ The authors express their appreciation to G. M. Spurlock for his assistance in making available the original Barbados ewes and to D. Torell, M. Dally and J. Hays for assistance with collection of the data. Supported in part by the Small Ruminant CRSP, U.S. AID Grant DSAN-XII-0049.

² The Agr. Inst., Grange, Dunsany, Co. Meath, Ireland.

³ Dept. of Anim. Sci.