Activity of the genital tract and plasma levels of oxytocin and cortisol at the time of mating in the ewe

Abstract

Experiments were conducted in the ewe to determine the effects of mating on the activity of the genital tract and on blood levels of oxytocin and cortisol. The activity of the uterus and cervix was recorded by electromyography, oxytocin was measured by radioimmunoassay, and cortisol by high performance liquid chromatography. Mating itself did not increase circulating oxytocin or cortisol; uterine motility remained unchanged during and after copulation but the cervix was significantly stimulated during teasing and after copulation. It is suggested that increased cervical activity resulting from adrenergic mechanisms may facilitate the generation of a cervical reserve of spermatozoa.

Plasma levels of cortisol and oxytocin, and uterine activity after cervical artificial insemination in the ewe

“…Because AI was performed using a catheter empty of semen, it is concluded that these endocrine responses were due to environmental and genital stimuli associated with the handling of animals and the AI procedure only. By comparison, earlier studies in the same species had reported that stimuli associated with mating, such as olfactory, visual and tactile signals, and then coitus did not modify plasma levels of CORT and OT [12,26].…”

“…However, it is also well established that strong peristalsis does not facilitate sperm transport, but often reduces fertility [22,25]. Indeed, the uterus responds to mating by increasing its contractile rate, but only transiently, for less than 1 min in the ewe [12,42] and macaque [14,44], or for no longer than 2 min in the rabbit [11] and woman [10]. Therefore, it is tempting to speculate that a secretion of OT altering the contractile rate of the uterus for a long period is detrimental to fertility in a number of species, including the ewe.…”

“…Furthermore, there is evidence that in an attempt to enhance sperm transport, such an OT treatment in the ewe considerably diminishes the number of spermatozoa recovered in the fallopian tubes after insemination [27]. On the contrary, since a reflex release of OT does not occur at mating in the ewe [12,26], as in the cow [42], it is assumed that OT does not play a significant role in sperm transport in these species. These observations account for interspecies differences, since an OT release in response to mating has been demonstrated in sows [5], and results from a higher stimulation of the genital tract when intra-uterine deposition of semen occurs.…”

“…In the estrus ewe, this supports the idea that a change in the motor pattern may occur when the speculum is inserted and opened into the vagina, and may account for low fertility when this procedure is used for cervical AI. According to earlier studies, vaginal dilation at estrus is effective in evoking a reflex release of oxytocin (OT) from the pituitary gland [1,35,38], which in turn stimulates uterine motility [12]. In the ewe, although Prud'homme and Rousseau [34] reported that a hypophysectomy abolished the uterine response to vaginal stimulation with a speculum, suggesting a reflex release of OT, no study has investigated OT secretion during routine procedures for cervical AI in this species.…”

“…Using electromyography, Van der Weyden [49] reported that environmental disturbances during estrus (such as the presence of an observer in the stable) induced an increase in uterine activity. Since plasma cortisol (CORT) levels remain unchanged after mating in the ewe, and that uterine motility was not stimulated, or very briefly (less than 1 min) [12], it is suggested that the absence of normal mating stimuli, together with stress during the AI procedure, may affect uterine motility for a long period.…”