Lactation: No End in Sight

My mare foaled in November 2007 and to date (Feb. 2011), she still produces enough milk that when you…
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Q:My mare foaled in November 2007 and to date (February 2011), still produces enough milk that … when you squeeze her nipple, a stream occurs. The bag is not extended, but milk is always present. A couple of years ago my veterinarian gave her a shot to help dry up the milk production, and we were going to follow up with a second shot, but she developed a case of laminitis and I did not continue the treatment. There do not seem to be any behavioral or cycling problems, and she can still be ridden with other horses.

Susan Summers, via e-mail

A: Causes of galactorrhea (abnormal milk production) are not well-defined. Most commonly the cause is attributed to an elevation in prolactin secondary to equine Cushing’s disease, so this problem should be ruled out first–especially if your mare is older. Prolactin is a hormone that stimulates mammary gland development and milk secretion.

Prolactin is produced within the brain tissue, and a neurotransmitter called dopamine keeps its production in check. Horses with Cushing’s disease are deficient in dopamine. A drug called pergolide is the treatment of choice for Cushing’s; this drug stimulates dopamine release, and this in turn decreases the prolactin secretion. Pergolide treatment should ultimately cause a drop in prolactin, decrease mammary development, and stop milk production in your mare if she has Cushing’s

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Written by:

Lucas Pantaleon, DVM, Dipl. ACVIM, is an equine internal medicine specialist.

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