Simultaneous recording of pituitary oxytocin secretion and myometrial activity in oestrous mares exposed to various breeding stimuli.

This study examined the effect of different mating stimuli on the uterine contractions and pituitary oxytocin release in horses during their breeding cycle, with the goal of improving treatments for horses with faulty uterine clearing mechanisms.

Study Design and Methodology

• The research involved five mares during their oestrous (breeding) cycle.
• Surgical procedures were used to implant electrodes and strain gauges on the uterine myometrium (the middle layer of the uterine wall).
• A graph was used to monitor myometrial activity, which involves the contraction of the myometrium.
• Two catheters were inserted non-surgically in each mare, one in the intercavernous sinus to draw pituitary venous blood samples and another in the jugular vein.
• Continuous sampling was carried out for two hours to establish baseline values for uterine contraction and pituitary oxytocin release.
• Four mating stimuli were applied sequentially: a stallion call, visual contact with a stallion, active teasing, and artificial insemination.

Results of the Study

• During the baseline recording, no relationship was observed between the episodes of uterine contraction and pituitary oxytocin release.
• When the mares were presented with any of the breeding stimuli, rapid onset of myometrial contractions was noted (P < 0.0001).
• The application of a stimulus noticeably increased pituitary oxytocin release (P < 0.02) and contraction duration (P < 0.05).
• Among the responses to all treatments, the reaction to artificial insemination was the most extreme (P < 0.05).
• In most cases, the onset of oxytocin secretion occurred simultaneously with the increase in uterine contraction, rather than preceding it, suggesting a less likely causal relationship between them.

Conclusion of the Study

• Interactions, even visual or auditory, between stallions and mares contribute significantly to the uterine clearance mechanism around breeding time.
• Understanding these physiological responses could assist in creating therapeutic regimens for mares suffering from endometritis due to inadequate uterine contractions.