EFFECTS OF ENERGY LEVELS IMPOSED BEFORE OR DURING THE ESTROUS SEASON ON RATES AND LOCATIONS OF OVULATION IN SHEEP

Abstract

Forty-five crossbred ewes were randomly assigned to two feeding energy regimes (high, H; low, L) 6 wk before the expected onset of the first estrus and were randomly reassigned 3 days after the second estrus. Although the date of the first observed estrus was similar for both groups, the mean weight of ewes in the H group was 5.3 kg more than the average in the L group (P < 0.05). At the first and second estrous periods, respectively, 18 and 20% more of the ewes in the H group had multiple ovulations. At both the third and fourth estrous periods, 68% of the ewes in the H regime had multiple ovulations as compared to 44 and 26%, respectively, for ewes in the L regime (P < 0.05 at the fourth estrus). The ovulation rate at an estrus was more dependent upon the feeding energy level imposed during that estrous period than upon exposure during previous periods. Among the four estrous periods studied, the only significant increase in ovulation rates occurred between the first and second estrus. The location of the corpus luteum at one estrus had no significant effect on the location of the next ovulation.