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Oxytocin uses at foaling

Oxytocin uses at foaling
Oxytocin uses at foaling


Oxytocinís affect on the uterus makes it a very important hormone in a horse breeding program.  This naturally occurring compound is released in increasing amounts during the last few days before foaling.  The effect of oxytocin released into the blood stream is to start contractions of the uterus and release milk from the udder.

Oxytocinís affect on the uterus is to stimulate contraction of the muscles. The uterine muscles are both longitudinal and circular.  The circular muscles tighten around the fetus and the surrounding fluids.  This has the affect of squeezing a water filled balloon. In an attempt to relieve pressure, the fluid filled placenta will search for an escape.  The relaxed cervix waiting for the birth provides the needed escape. As the placenta pushes through the cervix, it widens it which allows more movement, etc.  This in turn stimulates more oxytocin release which starts affecting the longitudinal muscles.  These muscles contract from the ovary end toward the cervix.  This movement of the uterine contents helps to propel them out the cervix.  The continued affect on the uterus after foaling helps the placenta separate from the uterine lining and be passed out.

The above mentioned release of oxytocin also affects the udder. As the blood levels increase we see the udder fill as milk is released from the tissue.  Prior to this let down, the teat ends would almost touch.  With filling by colostrum, the teats will be pointing down, indicating foaling will happen within 24 hours, usually!

Following foaling, each time the foal nudges the udder a signal is sent to the pituitary to release oxytocin.  The affect is to release milk from the udder tissue and into the teats.  Another important affect is the contraction of the uterus, and stimulation of uterine clearance of the products left over from foaling.  Each time the foal nurses, it is helping improve the condition of the uterus and the chances of a successful rebreeding.

We are fortunate to have such an important hormone available for our use.  While it has been around for a very long time, new research is confirming how important it is.  This very versatile drug is used immediately post partum, during treatments and during the breeding process. The dosage is very small and can be given intramuscularly (IM), subcutaneously (SQ), or intravenously (IV).  The onset of action for oxytocin is rapid and its affect on the mare can be seen within minutes. The action and the signs of effectiveness will be discussed below.

We have discussed the affects of the mareís own oxytocin at the time of foaling.  Due to the strong affect the medicine has on the very large uterus, we do not use oxytocin on the day of foaling.  While there is usually some cramping as the uterus closes the space the foal spent the last eleven month, oxytocin will intensify the discomfort. The signs of cramping are similar to those of colic.  The mare may try to lay down and roll while trying to find a comfortable location.  With a newborn foal laying around, this can be a threat.   

Using oxytocin during the first few hours after foaling also increases the risk of prolapsing the uterus.  It is already very active and oxytocin only increases the strength of contractions.

The exceptions to this rule are two:
If the mare has milk in her udder, but refuses to let the foal nurse, oxytocin is used to stimulate milk let down.  This will engorge the udder signally the mare she needs to be nursed.  In addition, oxytocin has a calming affect on the mare and will make her more receptive to the foal. This is especially of interest to the filly foaling for the first time as she adapts to this strange, wet, spindly, creature as it follows her around trying to reach between her hind legs.  The calming affect is not strong so in some of these situations the veterinarian may need to recommend tranquillizers or restraint.

If the mare is receptive and her udder is full, oxytocin should not be given as it will only fill the udder more, making it even more sensitive and increasing the discomfort of nursing.

The other exception is if the mare retains her placenta.  Oxytocin in very small doses stimulates stronger contractions which help the uterus and placenta separate.

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