Effects of body condition and environmental stress on ovulation rate, embryo survival, and associated plasma follicle stimulating hormone, luteinizing hormone, prolactin and progesterone profiles in Scottish Blackface ewes

Abstract

ABSTRACTIn a 2 × 2 factorial experiment, half of each of two groups of ewes in high (20 ewes) or low body condition (20 ewes) were subjected to procedures designed to simulate normal management and climatic stresses, and the effects of these treatments on ovulation rate, embryo survival and endocrine status were investigated.The mean ovulation rate of ewes in the high condition group was significantly higher than that of ewes in the low condition group (1·8 v. 11) (P < 0·001). Embryo survival rates were unaffected. Neither ovulation rate nor embryo survival were affected by stressful treatments.Circulating follicle stimulating hormone, luteinizing hormone and prolactin levels were recorded in the peri-ovulatory period. Mean circulating follicle stimulating hormone levels were similar in three of the treatment groups but were generally lower in ewes in the low condition/stressed group. This difference was significant in some of the sampling periods. Neither basal levels of luteinizing hormone nor the size of the pre-ovulatory luteinizing hormone surge were significantly affected by level of body condition or stress but the surge began earlier in ewes in the low condition groups. The difference in timing was not, however, related to ovulation rate. Circulating prolactin levels were consistently and often significantly lower in ewes in poor condition (P < 0·05). Levels were not significantly affected by stress.While ovulation rate was affected by body condition, the recorded progesterone profiles during the first 2 weeks after mating suggest that luteal function was not affected by any of the treatments applied.