Endocrine responses to standardized cervical manipulation in the mare

Abstract

IntroductionManipulations of the cervix are a prerequisite for numerous diagnostic and therapeutic techniques in equine gynaecology, obstetrics and reproductive biotechnology such as endometrial swabs, cytology and biopsies, palpation of the vaginal portion of the cervix, intrauterine insemination and instillation, therapeutic uterine flushing, embryo collection and transfer, and surgery of the cervix. Depending on the reproductive status of the mare, knowledge of the effects of cervical manipulations would allow avoiding negative consequences for the reproductive success in mares.The effects of cervical manipulations on oestrous cycle and early pregnancy in the mare have been under discussion for decades. Insertion of aluminum rods into the cervical canal did not change oestrous cycle patterns (Arthur 1975). In contrast, Hurtgen (1975), Hurtgen and Whitmore (1978) and Hurtgen and Ganjam (1979) were able to shorten dioestrus in mares by simply dilating the cervix manually. Moreover, Berglund et al. (1982) SummaryThe impact of manipulations of the equine cervix on the endocrine system, oestrous cycle patterns, pregnancy rates and embryonic development was investigated by six studies in cyclic and inseminated pregnant mares. In cyclic mares, standardized cervical dilation at Day 7 after ovulation (Day 0 = ovulation) shortened luteal phase and oestrous cycle by almost 2 days. Cervical dilation did not provoke an immediate release of PGF2α, but stimulated a distinct secretion of oxytocin. Starting from Day 10, dilated mares showed significantly lower progesterone levels and went two days earlier into luteolysis compared with controls. Administration of xylazine hydrochloride blocked the oxytocin release completely and oestrous cycle length was not altered by combined treatments. In inseminated, pregnant mares, dilation of the equine cervix did not affect pregnancy rates and early embryonic growth rates. Cervical manipulation also stimulated the secretion of oxytocin, but plasma levels of progesterone did not vary among groups. In contrast, dilated mares treated with xylazine hydrochloride did not secrete oxytocin, but progesterone levels tended to be lower compared with untreated controls (xylazine hydrochloride only). Surprisingly, embryonic growth rates were significantly higher in dilated mares pretreated with xylazine hydrochloride compared with controls. Cervical dilation did not change plasma concentration patterns of LH and prolactin with one exception. Only one pregnant mare showed a distinct rise of prolactin after cervical dilation. Moreover, this mare was the only one, which developed endometrial inflammation and subsequent embryonic death by Day 12. This observation needs to be investigated further for clarification of a possible contribution of prolactin to the mechanisms involved. Additionally, the role of xylazine has to be evaluated, because there is no further evidence from our data that the inhibition of oxytocin release is of significance concerning the effects on embryonic growth by combined tre...