FSH and LH activity of PMSG from mares at different stages of gestation

Blood was collected from each of four mares at approximately 60, 90 and 120 days of pregnancy. Pregnant mare serum gonadotrophin (PMSG) was prepared in a relatively impure form from each serum sample. Biological activities of FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone) were determined for each sample. FSH activity was greatest at 60 days of gestation and was reduced by day 90; this reduction persisted through day 120. LH activity was highly variable among mares at 60 and 120 days, and variability and mean values were lowest at 90 days. The mean ratio of FSH to LH was greatest at 90 days. The mean ratio of FSH to LH was greatest at 90 days and somewhat lower at both 60 and 120 days. The results suggest that the composition and biological activity of PMSG, as prepared and assayed by these procedures, may vary during gestation as well as among mares.