Some steroids in the blood of mares suffering from endometritis and post-partum mares as compared to normal cycling mares.

It appeared that in mares suffering from endometritis the concentrations of pregnenolone, of the compound "5.4", and of progesterone in the blood during the first 2 days of the heat period were significantly higher than in normal cycling mares, in which the concentrations of all steroids were less than or equal to 1 ng/ml. In five endometritis mares the "5.4" and progesterone concentrations decreased after the first days of the heat period, and at about two days before ovulation the values were comparable to those of normal cycling mares. Eight mares suffering from a severe endometritis did not ovulate, their oestrous period was prolonged, and the follicles became atretic. Possibly the relatively high progesterone content found in these mares, caused the reduction of the follicular growth, and this might explain the prolonged oestrous period which is observed in many mares suffering from endometritis. Often we observed in post-partum mares the same changes in concentration as in endometritis mares. An elevated level of these steroids was sometimes found in the blood a few days after foaling and, in four of eight post-partum mares, during the foal heat. Most probably this was caused by infection or stimulation of the uterus. The hypothesis is advanced that progesterone originating in the uterus can influence ovarian activity and that it may be one of the factors responsible for the anoestrous periods which can occur in mares with endometritis and in post-partum mares.