Effects of prolonged exposure of ewes to oestrogenic pasture 2. Occurrence of abnormalities of the external genitalia and altered mating performance

Abstract

Abstract Romney ewes grazed pasture initially containing 0 (C), 30 (M), or 60% (P) Pawera red clover for c. 6 months per year (spring-autumn) during the first 4 (P) or 5 (M) years of a 6-year study. When not grazing red clover, all animals grazed C-type pastures. In Years 3–6, ewes were scored on a subjective 0–3 scale for vaginal abnormalities. More of the animals grazing M pasture scored 1 or higher each year compared to the ewes on C pasture (P < 0.001). Similarly, more of the ewes grazing P herbage were scored 2 or higher than either of the other two groups (P < 0.001). A greater proportion of the ewes on the P sward were mated more than once at each joining, compared with the other two groups (P < 0.01 in Year 3; P < 0.001 in all other years) and consequently there were differences in the mean number of times each ewe was mated. Long-term grazing of oestrogenic red clover results in both a high incidence of abnormalities of the external genitalia and decreased mating performance in ewes. However, the...