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Effect of Level and Sequence of Feeding and Breed on Ovulation Rate, Embryo Survival and Fetal Growth in the Mature Ewe¹

University of Wisconsin, Madison

Abstract

Ovulation rate, embryo survival and fetal growth at 140 days of gestation were studied at slaughter in 80 Hampshire and 88 Columbia mature ewes. Straight-bred and reciprocal crossbred fetuses were produced by mating purebred Hampshire and Columbia rams to the two breeds of ewes. The ewes were subjected to flushing (grain feeding) for periods ranging from 0 to 87 days prior to breeding and then placed on either limited (ad libitum fed hay) or full (ad libitum hay plus 2 lb. grain daily) feeding from breeding until 140 days gestation.

A highly significant breed difference in ovulation rate in favor of the Hampshire ewes was found. Flushing produced a significant increase in ovulation rate in the Columbia but not in the Hampshire ewes; however, the breed-feed interaction was nonsignificant.

Evidence suggesting a negative genetic correlation between additive genetic contribution and maternal environment in response to gestation feed level effects on fetal survival was found.

Grain feeding during gestation increased all fetal body characters measured in both single and twin fetuses. Hampshire dams produced heavier single fetuses than Columbia dams, and twin fetuses sired by Hampshire rams tended to be heavier than those sired by Columbia rams.

Non-additive gene action was in evidence in the Columbia-Hampshire crossbred fetuses. The genetic contribution of the Columbia breed appeared to be dominant to the Hampshire breed in its effect on shin bone length in single fetuses.

Between pairs of twin fetuses at 140 days of gestation, fetal cotyledon weight had a significant direct effect on fetus weight which was greater than its indirect effect through fetal membrane weight. This relationship was not evident between fetuses of twin pairs.

An age difference between yearling and mature ewes of the same breed in response to flushing, embryo survival and feed effects on fetal growth is suggested.

¹ Paper from the Division of Genetics, No. 897 and from the Department of Meat and Animal Science, No. 359. Published with the approval of the Director of the Agricultural Experiment Station.

² Present address: U. S. Range Livestock Experiment Station, Miles City, Montana.