Early pregnancy diagnosis in the mare by estimation of the level of progesterone in the peripheral blood

Abstract

During the 3 weeks which follow the end of oestrus, in the course of which mating takes place, only 60% of non-pregnant mares are found by the traditional method of detection of oestrus. An equal percentage of non-pregnant females can be detected by a rapid estimation of the level of progesterone in the peripheral plasma carried out systematically 18 days after the end of oestrus. The animals found by one or the other method are always non-pregnant, but they are not all the same animals. Since the detection of oestrus is necessary for insemination, we propose to carry out the rapid progesterone analysis only on those females not returning to oestrus. The diagnosis thus realised when the mare refuses the stallion for 15–23 days after insemination, allows us to detect, without error, 50% of those which are not, however, pregnant. Using an identical analysis carried out on weekly samples, it is possible to distinguish several sorts of ovarian activity in the animals not showing oestrous cycles: maintenance of the luteal phase, silent ovulations, or prolonged absence of luteal activity.