The Horse

JAN 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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26 January 2019 The Horse | Steroids Steroids—both endogenous (produced naturally by the mare) and exogenous (ad- ministered by a human)—can affect the fetus. Examples of endogenous steroids include testosterone and progesterone. Some breeders administer the pro- gestin altrenogest (e.g., Regu-Mate) to mares in early pregnancy to prevent pregnancy loss associated with placentitis or low progesterone levels. The theory is it causes the cervix to remain closed and the uterus firm. While many veterinarians consider it safe for use in at-risk mares (e.g., those with a history of repeated pregnancy loss), they don't advocate for its use in healthy pregnant mares. "It is commonly used as a supplement for progesterone during pregnancy but may alter the local immune system and result in a decreased immune response in the mare," says Linton. Other exogenous steroids include those administered in joint injections, to treat hives or other allergic responses, or to treat shock. "They're the best anti- inflammatory we have," says Linton. "Yet steroids can also trigger labor, because labor is stimulated by a big steroid release from the fetus when it's ready to be born." If you're considering having your veterinarian inject your pregnant mare's joints, first ask yourself if she really needs it. "If she has hock arthritis and is so un- comfortable she won't lie down, and she's really lame, we might decide that giving her a hock injection would improve her overall clinical condition enough that it would be better for the fetus," says Lin- ton. "On the other hand, if you are simply routinely giving hock injections every six months, you might hold off on those while she is pregnant." A small amount of steroid injected into a joint might be less likely to cause systemic issues and affect the fetus than steroids given systemically, however, be- cause less would enter the bloodstream. Sheerin says veterinarians have admin- istered ophthalmic ointments containing low doses of corticosteroids for multiple days without much adverse effect. One risk when giving steroids, however, is the potential for developing laminitis, says Linton. "If a pregnant mare has something similar to gestational diabetes, she is already at risk for developing lami- nitis," she says. "A low dose of steroids that ordinarily would not cause laminitis could push her over that edge." Taking these factors and more into con- sideration, your veterinarian will weigh steroid administration in the pregnant mare on a case-by-case basis. Dewormers Most dewormers are labeled as safe for use in pregnant mares at the appropriate dose. An overdose of praziquantel or iver- mectin (both safe for broodmares), says Linton, can be toxic, but typically only in very high doses—more than 10 times the weight dose of ivermectin, for instance. "With dewormers, the biggest thing is to read labels," says Sheerin, noting that even with those approved for use in pregnant mares, many vets warn against giving them within 30 days of foaling and advise waiting until after the mare foals. If you have a good parasite control program, trying to keep the environment relatively free of parasite eggs, doing fecal egg counts, and deworming horses as needed, the mare might not need to be dewormed while pregnant. "You can probably wait until after she foals and have a strategy and management plan to help avoid having to give dewormers frequently," says Sheerin. Anti-Ulcer Medications Other drugs given to pregnant mares include anti-ulcer medications such as omeprazole (e.g., GastroGard), even though the label says safety for use in pregnant mares has not been determined. In the absence of data during pregnancy and lactation, veterinarians warn against administering GastroGard in pregnant and lactating mares, says Sheerin. "Anti-ulcer medications have not been shown to have negative effects in the fe- tus, but should only be used when gastric ulcers have been definitively diagnosed by a veterinarian," Linton says. Domperidone One drug that is safe is the dopa- mine antagonist domperidone, labeled to prevent fescue toxicosis in pregnant mares. Ingesting tall fescue infected with endophyte—a fungus that produces harmful alkaloids—is toxic to pregnant mares, particularly in the third trimester. If a mare can't be removed from an af- fected pasture in late pregnancy, veteri- narians might prescribe domperidone to block the toxin. Take-Home Message Giving medications to pregnant mares is never without risk and should always be discussed with your veterinarian. "Even then, owners can't expect their veterinarian to have a wealth of informa- tion on this topic because we don't have that much data," says Macpherson. Horse owners and vets try to make the best decisions possible—in the interest of the mare and foal's health—with the in- formation available, but there is still a lot of research to be done. When in doubt, consider with your vet whether your mare really needs a certain medication. h MEDS FOR MARES Read Labels Read the labels of any medications before administering them to pregnant mares. Some will clearly say, "Do not use in pregnant mares," while others have simply not been tested in that population. "Some drugs have not had enough testing in pregnant animals to have safety claims," says Jennifer Linton, VMD, Dipl. ACT, assistant professor of clinical studies at the University of Pennsylvania School of Veterinary Medicine's New Bolton Center, in Kennett Square. "For instance, rabies vaccines are not labeled for use in pregnant mares just because pharmaceu- tical companies have not done the studies that meet the requirements for them to state that information. Yet most of us include rabies in the vaccines we give mares ahead of foaling, because we want them to be protected and to provide antibodies in colostrum for their foals." So just because certain drugs or vaccine labels say they are not tested or certified for use in pregnant mares does not mean you can't use them. "It may simply mean testing has not been done to the level USDA requires," she says. "Ask your veterinarian about these. Your vet may call a referral clinic or a reproductive specialist to answer some of these questions." —Heather Smith Thomas

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