Ins and Outs of Equine Lactation

Lactation is a very important function in a mare. So important, in fact, that two lives depend on it. A mare's body will sacrifice her foal's health to save her own life ... both during gestation and after foaling. In other words, you must feed her adequately to maintain her body condition with surplus calories to feed the placenta during gestation and to make milk to fill the udder after foaling.

Many nutritionists believe pregnant mares should be fed the same as nonpregnant mares until the last third of gestation, when nutrient intake might increase to 1.3 times the level of the nonpregnant horse.

During the heaviest lactation periods, a mare might require 1.5 to 1.7 times the nonpregnant horse's nutrient density, and she might need 50-75% more water. Mares that have had foals before might start producing milk in the final 30 days of gestation. Maiden mares might also secrete milk during this time, but many will not produce milk until the hours before foaling. Both situations are considered normal.

A few potential lactation issues follow:

Mastitis, inflammation of the mammary gland(s), is most often seen at weaning. Keep a watchful eye on mares for one to two weeks after you wean a foal at 4-6 months of age. The alveolar cells of the udder will continue to secrete milk, and the udder will become distended. As it distends, a negative feedback loop occurs, milk production decreases, and distension subsides. If the well-meaning owner continues to manually express ("milk") the udder, more milk will be secreted and the udder will not decrease in size. Removing the foal from the mare's view and reducing her feed intake will decrease milk production. Your vet can easily diagnose mastitis, which can present with pain, fever, hind limb lameness, and, occasionally, anorexia. After diagnosis and treatment, the mare usually recovers in less than a week.

Lactation tetany (often called "eclampsia" in farm animals) rarely occurs in horses. It develops when heavily lactating mares are exposed to work requiring muscle contraction, since calcium stores are required for muscle activity.

Agalactia is the absence of milk production (when it should be present). Almost all cases result from ingesting fescue-type grasses contaminated with Claviceps spp. This ergot alkaloid-producing fungus contaminates up to 70% of U.S. fescue. Ergot alkaloids also cause thickened fetal membranes, prolonged gestation, abortion, and premature rupture of the chorioallantois (red-bag delivery). Ergot alkaloids reduce prolactin (a lactation hormone) secretion since they are dopamine agonists (activators). To treat ergot-caused agalactia, use dopamine antagonists (domperidone, reserpine, and sulpiride), and phenothiazine tranquilizers (acepromazine). Pregnant mares can graze fescue, but remove them from fescue-contaminated pastures during the last 90 days of gestation and provide alfalfa with high levels of available calcium.

Galactorrhea is spontaneous lactation. Impending abortion or premature foaling of a twin pregnancy might trigger lactation. Premature lactation, a subset of galactorrhea, is a common cause of colostrum loss and failure of neonate passive transfer. Vets should evaluate the immunoglobin G (IgG, plasma proteins that defend against foreign invaders) transfer status of foals born to mares dripping milk when the foal is 6-8 hours old--when passive transfer is almost 85% complete--to ascertain the need for supplemental colostrum/plasma. If there has been a partial failure, there is time for colostrum absorption before resorting to plasma. In the past many vets have waited until foals were 24 hours old to check IgG status, but by then colostrum cannot be absorbed in appreciable amounts and plasma is the only option--and it's a costly one.

Inappropriate lactation is another subset of galactorrhea. In female neonates or weanlings, the filling of the udder is called "witch's milk." Lactogenic chemicals accessed through the dam's udder or blood circulation cause this condition, and no treatment is recommended.

About the Author

Benjamin Espy, DVM, Dipl. ACT

Benjamin Espy, DVM, Dipl. ACT (boarded in equine reproduction), has practiced veterinary medicine in Texas and Kentucky. He has been licensed to practice acupuncture for nine years and is on numerous AAEP committees and task forces. Espy serves on the alternative therapy committee for the Texas Veterinary Medical Association, and he's an animal treatment consultant for the Professional Rodeo Cowboys Association.

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