Association of uterine edema with follicle waves around the onset of the breeding season in pony mares.

During spring transition, when estrus may be exhibited for prolonged periods, it is important for veterinarians and stud farm personnel to be able to predict whether a large follicle will ovulate or regress. It is thought that the presence of ultrasonically detectable uterine edema indicates that a follicle will ovulate, however, there is little evidence to support this. In the present study, 16 mares were regularly examined by transrectal ultrasonography to follow growth and regression of follicles from seasonal anestrus in February until second ovulation. Blood samples were collected daily for measurement of estradiol concentrations when a large ovarian follicle was present. Estrous-like uterine edema was detected during 7 of 11 (64%) anovulatory follicle waves, in 12 of 14 (86%) mares before their first ovulation, and in 100% of mares before their second ovulation. Uterine edema was first detected 43+/-6.7 days before first ovulation. Large anovulatory follicles tended to be present for longer periods of time than ovulatory follicles. Uterine edema was present for a significantly greater proportion of time in the presence of a large follicle at second ovulation than at first ovulation (P<0.05) or for anovulatory follicles (P<0.01). Peak plasma estradiol concentrations and mean plasma estradiol concentrations were significantly higher (P<0.001) when a dominant preovulatory follicle was present compared with a dominant anovulatory follicle, but there was no difference in estradiol concentrations between first and second ovulations. It was apparent, therefore, that uterine edema was not a reliable indicator of follicular steroidogenic competence, or of whether the follicle would ovulate.

Release of oxytocin and prostaglandin f(2alpha) around teasing, natural service and associated events in the mare.

Mating has been shown in many species to provoke the release of oxytocin (OT). In our study, various stimuli were applied to mares to study release of OT and prostaglandin F(2alpha) (PGF(2alpha)) associated with mating. Blood samples were collected from mares around the time of teasing both in oestrus and dioestrus and at mating. For comparison, blood samples were also collected at the time of manual manipulation of the genital tract and after intrauterine infusion of 500 ml phosphate buffered saline (PBS). Additional samples were collected 16 to 18 h after mating. Mating caused a significant increase in OT in all mares and teasing caused a significant OT response in 6 of 10 oestrous and 3 of 5 dioestrous mares. However, mating and teasing had no significant effect on concentrations of 15-keto-13,14-dihydro-PGF(2alpha) (PGFM). Manual manipulation of the clitoris, vagina and cervix caused significant OT release in all mares and intrauterine infusion of 500 ml PBS caused significant OT release in three of the five mares. However, only one mare had a significant PGF(2alpha) response during manual manipulation and only one responded positively to intrauterine infusion of 500 ml PBS. We concluded that events around mating, including stimulation of the genital tract and uterine distension, often caused an increase in circulating concentrations of OT but only rarely in PGFM.

Immunolocalization of oxytocin and neurophysin in the mare uterus.

The presence of oxytocin in the mare uterus was determined by radioimmunoassay of tissue extracts and uterine lavage fluid, and by immunohistochemistry. Samples were obtained from mares during the oestrous cycle and on day 14 of pregnancy. Immunoreactive oxytocin was detected in extracts of endometrium and myometrium, and in uterine lavage fluid. In tissue sections, the luminal epithelium, the epithelium of the superficial, but not deep, glands, blood vessel walls and myometrium all stained positively for oxytocin, whereas only the luminal epithelium and epithelium of the superficial glands stained positively for neurophysin. These results indicate that oxytocin is synthesized in the epithelium but not in the myometrium. Immunostaining for oxytocin was most intense in early pregnancy and least intense during mid- to late dioestrus. The great variation in staining density during different reproductive states indicates that uterine oxytocin may have an autocrine or paracrine role in controlling uterine function.

Oxytocin and PGF2alpha release in mares resistant and susceptible to persistent mating-induced endometritis.

Mares resistant (n=7) and susceptible (n=9) to persistent mating-induced endometritis were artificially inseminated (AI) during oestrus with chilled extended semen. Blood samples were collected from 30 min before AI, for 2 h after AI and again between 16 and 18 h after AI. Samples were assayed for oxytocin and the PGF2alpha metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM). AI caused a significant increase in oxytocin concentrations in both the resistant and susceptible mares and there was no significant difference in oxytocin release between the two groups of mares. Mean PGFM concentrations were significantly higher in the resistant group for the first 30 min after AI. In a second experiment, an i.v. injection of oxytocin (1 iu per 20 kg body weight) was administered to both resistant and susceptible oestrous mares. Blood samples were collected at 5min intervals from 10 min before until 60 min after oxytocin administration. Administration of exogenous oxytocin caused significantly greater PGF2alpha release in resistant than in susceptible mares. The observed pattern of decreased PGFM concentrations in the susceptible group of mares after both AI and oxytocin administration indicates a possible defect in PGF2alpha release at the oxytocin receptor or post-receptor level.

Oxytocin in the semen and gonads of the stallion.

It has been suggested that oxytocin is involved in sperm transport and motility in domestic animals. Immunoreactive oxytocin was measured in seminal fractions (pre-ejaculatory fluid, seminal plasma, gel and sperm) and in extracts of testis and epididymis from stallions. In addition, sections of gonadal tissue from stallions were immunostained for the presence of oxytocin and its neurophysin. Oxytocin was detected in all of the seminal fractions, being highest in the gel. It was also present in washed, lysed sperm and in extracts from the testis and epididymis. Immunostaining for oxytocin was present in occasional interstitial cells in the testis and in the epididymal epithelium and smooth muscle. However, immunostaining for neurophysin was detected in a few interstitial cells in the testis of only 1 of 8 stallions and was absent from all areas of the epididymis. These data demonstrate for the first time the presence of oxytocin in stallion semen and gonadal tissue; however, lack of immunostaining for neurophysin indicated that it was unlikely that there was local synthesis within the gonads.

Uterine contractility is necessary for the clearance of intrauterine fluid but not bacteria after bacterial infusion in the mare.

Bacteria were infused into the uteri of 5 estrous mares resistant to persistent mating-induced endometritis, first during a control cycle, and then during treatment with clenbuterol, a beta 2 agonist. Uterine cellular response was evaluated 48 h later by transrectal ultrasonography, followed by uterine lavage. During clenbuterol treatment all mares accumulated intrauterine fluid, whereas in the control cycle none of the mares retained fluid. There was no significant difference between the 2 cycles in the cloudiness of the lavage fluid, number of cells per milliliter, percentage of neutrophils and frequency of bacterial growth from the recovered fluid. We conclude that uterine contractility is important in the clearance of uterine fluid, but not necessarily for the elimination of bacteria, thus supporting the published evidence that impaired uterine contractility contributes to the pathogenesis of persistent mating-induced endometritis.

Does artificial insemination with chilled, extended semen reduce the antigenic challenge to the mare's uterus compared with natural service?

Uterine response in infection-resistant mares (n = 5) at 48 h after AI was compared with that following natural service in these same mares, and after AI in infection-susceptible mares (n = 6). In the resistant mares, small amounts of uterine fluid were detected and bacteria were isolated infrequently at 48 h after breeding, but cytological examination of uterine flushes revealed that a significant degree of endometritis was present. There was no difference in the degree of inflammatory response by 48 h after AI or natural mating. In 4 of the 6 susceptible mares moderate to large accumulations of intrauterine fluid were detected at 48 h after AI, and massive uterine neutrophilia was present in all 6 mares. It was concluded that there was no evidence that using conventional AI techniques limited the inflammatory response of the mare's uterus.