| Abstract: | Peripheral plasma progesterone and corticosteroid concentrations were studied in ewes grazing oestrogenic pastures during oestrus, pregnancy and parturition in 1974 and during pregnancy in 1975. Haemoglobin (Hb) type A ewes had significantly higher mean corticosteroid concentrations than HbB ewes in both years. In 1974 the concentration of progesterone did not differ significantly between Hb types whilst in 1975 the concentration was significantly (P less than 0.001) higher in HbA ewes. The mean corticosteroid concentrations were higher in selenium-supplemented ewes of both Hb types than in unsupplemented ewes in 1974 but lower in 1975. Selenium treatment did not significantly influence the progesterone concentration in ewes of both Hb types in 1974 but significantly (P less than 0.01) increased in 1975. It is concluded that the higher concentration of plasma corticosteroids or factors regulating the relationship between corticosteroids and progesterone could be responsible for the higher estimates of embryonic mortality reported in HbA ewes. |
