Characteristics of milk ejection, associated intramammary pressure changes and oxytocin release in the mare.

This research investigates the complex process of milk ejection in lactating horses, examining the role of oxytocin and intramammary pressure in this process. The study found that the suckling stimulation of the mammary gland and an oxytocin surge are not essential prerequisites for successful milk ejection.

Objective of the Study

• The study aimed to investigate the neuroendocrine reflex theory of milk ejection under natural suckling conditions in horses. The researched examined the role of intramammary pressure (IMP) changes and oxytocin release in the milk ejection process.

Research Methodology

• The researchers monitored 12 lactating mares, installing acute jugular catheters for blood drawing and intramammary pressure recording catheters. The foals had free access to the contralateral mammary complex.
• The researchers measured oxytocin levels in blood samples drawn during suckling while simultaneously recording intramammary pressure.

Findings of the Study

• Suckling periods involving a characteristic increase in IMP were significantly longer than unsuccessful nursing attempts. Moreover, physical stimulation of the mammary gland, a quiet phase, and a sudden increase in IMP were key elements of successful sucklings.
• Successful suckling usually occurred at intervals of around 20 minutes, but could vary from less than 5 minutes to more than 100 minutes.
• Oxytocin release was not always initiated before an increase in IMP. In some cases, the researchers were unable to detect an oxytocin surge, despite an increase in IMP associated with milk ejection.
• In three instances, an increase in IMP was observed even when the foals were away from the mares and showed no intention to suckle.

Conclusion of the Study

• The findings suggest that elements like physical stimulation of the teat and an oxytocin surge, which are part of the neuroendocrine reflex, are not absolute necessities for successful milk ejection in horses. This suggests that the process of milk ejection in horses might be more complex and not fully reliant on the established neuroendocrine reflex theory.