Effects of nutritional environment on breeding season in range sheep

TitleEffects of nutritional environment on breeding season in range sheep
Publication TypeConference Paper
Year of Publication1984
AuthorsHulet CV, Shupe, W. Larry, Ross T.T.
Conference NameJournal of Animal Science
Date Published1984
Keywordsbreeding season, nutrition, ovulation rate, range sheep

The objectives were to determine effects of the season, nutritional environment, and presence of the ram on incidence and rate of ovulation in finewool sheep in southern New Mexico. Mature ewes (144 head) were randomized into groups maintained either on arid Southwest range or in drylot on alfalfa hay (1.59 kg/head/day). These nutrition-environment groups were further randomized into ram-exposure subgroups to test effects of continuous or intermittent exposure (30-day periods) to sterile rams. Both drylot and range-managed ewes were in good condition and gained weight during the study (9.8 and 5.1 kg/ewe). Copora lutea were observed twice each month for 13 months in random samples of three to six ewes from each subgroup. Seasonality of ovulation in finewool sheep managed on the range was much more marked than in animals managed on alfalfa hay in drylot. The incidence of ovulation approached zero in the range-managed ewes during May, June, and July (8%, 0%, and 4%, respectively), compared with 42%, 17% and 75% for the alfalfa-drylot group (P<.02, P<.10, P<.01). Although the incidence of ovulation in the range-managed group increased to 50% in August, the incidence was still lower (P<.05) than in the drylot-hay group (83%). The incidence of ovulation also was lower (P<.01) in the range-managed than the drylot ewes during February (33% vs. 83%). Ovulation rate was highest in October (1.66) and November (1.63) and lowest in March (1.14) and May (1.14). The mean annual ovulation rate of the drylot group (1.48) was very similar (P>.10) to that of the range-managed group (1.39). Continuous or intermittent presence of a ram had no real effect on either the incidence or rate of ovulation. It is concluded that the nutritional environment can significantly affect seasonality of breeding in finewool range sheep. This may not be consistently modified by ram exposure.