Effect of oxytocin and seminal plasma treatment on uterine contractile activity and pregnancy rates in subfertile mares

Abstract

The aim of the study was to find out how reproductive disorders in problem mares, with a disposition to persistent mating induced endometritis, are related to dysfunctional uterine contractile activity (UCA). Additionally, seminal plasma, given into the uterus after insemination, and oxytocin administered immediately after insemination, were tested on their stimulating effects on uterine contractions and influence on pregnancy rates. Also the influence of UCA on uterine bacteriological and cytological findings before and after insemination was examined. The subfertile mares were inseminated into the uterine body 24 h and 48 h after hCG-administration and were treated immediately after AI with oxytocin (Group 1, n = 27 cycles) or additional seminal plasma (Group 2, n = 25 cycles) or were left untreated (Group 3, n = 30 cycles) after AI. Group 4 (healthy mares with foal,n = 12 cycles) was inseminated twice without further treatment and served as control. UCA was evaluated by transrectal ultrasonography 16 to 18 days after last estrus, before and after the first and second AI and 48 h after the second AI. Contractions were documented in a score-level-system (0-IV). Bacteriological and cytological samples were taken before the first and 48 h after the second AI. A uterine biopsy was analysed in interestrus before insemination. Significant differences in the UCA of the total group of mares were obtained between the different times of evaluation. Comparing the 4 treatment groups, the fertile control group showed in general stronger uterine contractions than the other groups. UCA between the fertile control and the oxytocin treated mares on the one side and the seminal plasma and untreated mares on the other side differed significantly. A positive correlation was shown between UCA and pregnancy results. The pregnancy rates differed significantly between the fertile control group (83 %) and the 3 experimental groups (40 %). There was no correlation between UCA and the results of the bacteriological and cytological samples of the endometrium. But there was a significant relationship between the results of the cytological sample obtained 48 h after the second insemination and the pregnancy results. Because of the positive correlation between UCA and pregnancy rate, poor uterine contractions are seen as one of the major causes of subfertility in mares. The present study demonstrated that uterine contractions are stimulated by artificial insemination and that consecutive inseminations even intensified uterine contractions. Barren mares showed in general a lower UCA than fertile mares did. To obtain good pregnancy results, also negative cytological swabs 48 h after insemination were important, since mares with positive results at this time had a minor chance of becoming pregnant. Based on these results optimal insemination frequency and way and time of uterine sampling should be discussed in the management of broodmares.