Histomorphological endometrial status and influence of oxytocin on the uterine drainage and pregnancy rate in mares.

The aim of this field study was to examine the influence of the uterotonic substance oxytocin in 2 different therapeutic dosages of 15 and 25 i.u., respectively on the uterine drainage of oestrous mares and on their fertility. In addition endometrial biopsies of mares with and without intrauterine fluid accumulations around the time of ovulation were evaluated histomorphologically regarding the aetiology of susceptibility to uterine infection. A population of 59 Hanoverian Warmblood mares was used in this study. The mares were divided into Group A (mares with intrauterine fluid accumulations [n = 49]) and Group B (controls [n = 10]). Group A was further subdivided into 3 groups according to varying oxytocin administrations (none, 15 i.u., 25 i.u.). Prior to insemination, all mares were examined by rectal palpation, ultrasonography and vaginal inspection. In addition, hormone plasma concentrations were evaluated at the time of ovulation, namely oestradiol and progesterone concentrations. Endometrial biopsies were obtained from all mares. Endometrial samples for microbiological and cytological evaluation were taken from mares of Group A only. All mares were inseminated close to ovulation during the first cycle. This study shows that intravenous oxytocin treatment of mares with intrauterine fluid accumulations results in better pregnancy rates than no treatment.