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Estradiol is the most active of the endogenous estrogens.
Estradiol cypionate (ECP) is an esterified estrogen that is more potent and
has a longer half-life than the predominant naturally occurring estrogen,
estradiol 17 beta. The actions of estrogen hormones on the female include
maturation of the reproductive tract and mammary glands, modulation of pituitary
gonadotropin secretion, expression of estrus behavior, enhanced uterine resistance
to infection, gestational support during pregnancy, and modulation of uterine
contractions and cervical relaxation during labor.
ECP is most commonly used in mares in order to enhance sexual receptivity in ovariectomized mares being used as stimulus mares in a semen collection program. ECP may also be used in a seasonally anestrous mare to produce sexual receptivity for the same purpose. Although the anestrous mare may be sexually receptive due to the effect of the ECP, if she is truly anestrous, she will of course not produce follicles or ovulate. ECP or other estrogens will not produce sexual receptivity in mares that are in diestrus with circulating progesterone.
Other less common uses for ECP in the mare include:
• Increasing sexual receptivity in mares that are
in physiological estrus but are still not receptive to the stallion.
• Silent heats" can be a real management headache when natural service
is necessary. The administration of exogenous estrogen has been tried under
these circumstances, but research has not been done in the horse to prove
whether or not there are any adverse effects on conception rates.
• Some labor induction protocols include the use of ECP to soften the
cervix prior to the administration of oxytocin.
• Some veterinarians use exogenous estrogens on mares while treating
uterine infections because research shows that the uterus is more effective
at clearing infection while under the influence of estrogen.
• Some researchers are working with exogenous estrogens or progesterone/
estrogen combinations for pregnancy maintenance in mares that habitually suffer
early embryonic loss.
• Many of these treatments are still in the research stages and the most
recent information should be consulted before embarking on treatment.
• Injection site reactions may occur. No other side
effects have been reported when ECP is used in ovariectomized mares.
• Estrogens are generally contraindicated in pregnant
mares. As noted above there is some research on their uses in mares with a
history of early pregnancy loss but our understanding of this process is still
evolving.
• Rifampin, phenobarbital and phenylbutazone may decrease estrogen
activity.
• The effects of glucocorticoids may be enhanced when used with estrogens.
The dose of corticosteroids may need to be reduced.
• No information regarding overdose was found.
Dr.
Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania.
She has a master's degree in animal science from the University of Delaware
and graduated from the University of Pennsylvania School of Veterinary Medicine
in 1982.
She began to develop her interest in client education and medical writing 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
The information contained on this site
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risks and benefits of using a particular product. You should consult your doctor
about diagnosis and treatment of any health problems. Information and statements
have not been evaluated by the Food and Drug Administration ("FDA"),
nor has the FDA approved the products to diagnose, cure or prevent disease.
Wedgewood compounded veterinary preparations are not intended for use in food and food-producing animals.
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