Ecbolic agents are those that have the ability to generate uterine contractions, the two most used products in equine reproduction are oxytocin and prostaglandin F2 alpha.
The application of ecbolics aims to expel the fluid that is accumulated in the uterus; which is usually found due to a mechanical disability (deficiency in myometrial contractions) or the body’s own drainage (lymphatic system) to defend itself against said alteration.
Normally mares that suffer from endometritis (inflammation of the endometrium) tend to retain fluid in the uterus, thus being prone to suffer from infections. Ecbolic agents are used in combination with uterine lavages as therapy to treat endometritis; however, they can be applied without the need for prior lavage with good results.
Oxytocin is the most used in equine reproduction, it is a synthetic hormone and the most used dose is 20 IU intravenously or intramuscularly; having an action of 30 to 50 minutes post injection. It can be administered with intervals of 4 to 6 hours daily; It is important that the interval is not less than this time because it can produce spasmodic contractions that are not beneficial for the evacuation of uterine fluid.
This hormone can be applied 6 hours after service with or without a uterine lavage to help remove semen or fluid; Some professionals recommend it with intervals of less or more than 6 hours after service. If necessary, its use is recommended up to 2 or 3 days after ovulation without affecting fertility. It is important to mention that on the day of service no pretreatment should be performed close to that time.
The hormone prostaglandin F2 alpha is another ecbolic agent known in equine reproductive practice to treat fluid retention in the uterus. Cloprostenol is a synthetic analogue of this hormone and the recommended dose is 250 µg intramuscularly. The action time of this product ranges from 2 to 4 hours after the injection, that is, it will generate uterine contractions for that time.
Unlike oxytocin, prostaglandin F2 alpha should not be administered after ovulation occurs; studies have shown that it decreases the serum concentration of progesterone (P4); and can affect the development of the next corpus luteum in formation, thus decreasing pregnancy rates. P4 is responsible for maintaining pregnancy and preparing the uterus to receive the embryo among other functions; and is produced by the corpus luteum (CL). PGF2 alpha has luteolytic action, that is, it is capable of eliminating CL.
Some side effects that may occur with the application of prostaglandin are sweating and abdominal pain (colic).
In some cases it is feasible to combine oxytocin and prostaglandin to obtain a better result in those mares where they do not respond correctly to the application of one of these products alone.
In the case of oxytocin, it has other uses in reproduction, this hormone can be used to induce labor in the mare; under certain necessary conditions. It is also suggested in the treatment of mares with retained placenta after foaling, as well as to promote milk let-down.
Prostaglandin F2 alpha, for its part, has effects on the corpus luteum and hemorrhagic follicles, eliminating them and thus causing the return of estrus; It has also been used to induce labor despite not being the preferred agent for this event.
University of Zulia, Faculty of Veterinary Sciences (FCV)
Member of the College of Veterinary Doctors of the state of Zulia, no. 2483
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