DIAGNOSTIC PROBLEMS ASSOCIATED WITH OVARIAN ACTIVITY IN BARREN AND POSTPARTUM MARES EARLY IN THE BREEDING-SEASON

Three studies were carried out to monitor or induce ovarian activity a nd sexual behaviour in maiden, barren and postpartum mares during the anovulatory season. In the first study maiden and barren mares were fo llowed up by regular blood sampling. In 39% of anoestrus mares the ano vulatory season was started after December 1. Mares that stopped cycli ng before December 1 had significantly longer anovulatory period (P<0. 001) and resumed cyclic ovarian activity one month later (P<0.01) than mares that stopped cycling after December 1. The first ovulation was not preceded by overt oestrus in most of the cases (64.7%). In the sec ond study 38 mares, foaling in the first three month of the year, were monitored. Cyclic ovarian activity resumed more than 20 days after pa rturition in 11 mares (28.9%, between 22 and 111 days). Only 52.6% of the animals showed heat before the first postpartum ovulation. The fol licular phase after the luteolysis of the first corpus luteum was long er than normal (>10days, between 22 and 64 days) in 10 mares (43.5%). In the third study 44 mares in spring transition were treated with Alt renogest for 10 days. In 8 treated mares a GnRH-challenge (40 mu g Bus erelin iv.) was carried out before treatment. Despite the same inclusi on criteria used for all mares, in case of II mares (25%) the treatmen t was not successful and the ovulation occurred more than 20 days afte r the end of treatment.(between 29 and 70 days). The result of the GnR H-stimulation gave an explanation for this difference. Mares that were treated successfully with Altrenogest had a higher maximum LH-respons e and area under the curve indicating higher LH-content of the pituita ry before treatment.