Oxytocin is a naturally occurring hormone found in all mammals, produced in the hypothalamus and released by the pituitary gland. It plays a broad role in social bonding and various reproductive processes. While often referred to as the “love hormone” due to its influence on connection, its actions extend significantly into physiological functions.
Primary Uses in Mares
Synthetic oxytocin is widely used in equine veterinary medicine to manage several reproductive conditions in broodmares. A primary application is to stimulate uterine contractions, useful for inducing or augmenting labor. Veterinarians may administer a low dose (typically 2.5 to 3.5 international units) to mares showing clear signs of impending parturition. This controlled approach often aims to shift foaling times to daylight hours, allowing for better supervision and intervention.
Oxytocin also assists in the expulsion of a retained placenta, a common post-foaling concern. Small, frequent doses (e.g., 20 IU intramuscularly every four hours) stimulate the uterine muscles to contract, helping to detach and expel the fetal membranes. This action also aids in clearing any bacterial or inflammatory debris.
The hormone further supports uterine involution, the process where the uterus shrinks back to its normal size after foaling. Regular administration (often 20 to 40 units intramuscularly once or twice daily) helps the uterine muscles “milk” out excess fluid and debris through the cervix. This physical clearance mechanism is beneficial for uterine health.
Beyond its role in uterine health, oxytocin stimulates milk let-down in nursing mares. It causes the smooth muscle cells surrounding the mammary glands to contract, releasing milk for the foal to access. This hormone increases milk availability but does not directly enhance overall milk production.
Behavioral and Stallion Applications
Oxytocin also addresses certain behavioral challenges in mares, particularly those involving mare-foal bonding. In instances where a mare rejects her foal or exhibits poor maternal behavior, controlled administration of oxytocin can encourage a stronger bond. Post-foaling mares show increased sensitivity to oxytocin, meaning smaller doses (5-10 IU) can be effective in promoting maternal instincts.
In stallions, oxytocin has been explored for its role in semen collection, especially when traditional methods are unsuccessful. While oxytocin concentrations naturally increase before ejaculation, its standalone use to induce ejaculation has shown varied results. However, some protocols combining oxytocin (e.g., 20 IU intravenously) with other pharmacological agents have successfully induced ex copula ejaculation, yielding good quality semen for breeding.
Administration and Safety Considerations
Oxytocin is a prescription medication and its administration should always be performed by or under the direct supervision of a licensed veterinarian. It is most commonly given by injection, typically via the intramuscular or subcutaneous route, though small doses can sometimes be administered intravenously. For obstetrical uses, a typical dose for horses is around 5.0 mL (100 USP Units), while for milk let-down, doses of 0.5 to 1.0 mL (10-20 USP Units) are often recommended.
Improper use of oxytocin carries significant safety risks for both the mare and the foal. It should never be administered if the mare’s cervix is not fully dilated, or if the fetus is positioned abnormally or is too large to pass through the birth canal. Doing so can lead to severe complications such as uterine rupture or fetal distress.
Mares may exhibit signs of mild colic, including pawing or kicking at their belly, shortly after receiving oxytocin due to uterine cramping. Higher or more frequent doses, or administering the hormone to a mare not physiologically ready for foaling, can result in the birth of weak or immature foals. To maintain efficacy, oxytocin should always be stored under refrigeration.