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The mare’s first milk, or colostrum, provides essential antibodies and is usually beneficial. In rare cases, however, this life-giver can prove toxic to her own foal.

The condition, termed neonatal isoerythrolysis (NI), can occur if a foal inherits the same blood type as his father. If his dam’s antibodies are directed against this blood type, the foal’s own red blood cells will be slowly destroyed as he ingests and absorbs colostrum.

He will quickly become pale and jaundiced, possibly suffering seizures and liver failure.

Lucy Brock MRCVS, of Twemlows Stud Farm in Shropshire, explains that broodmare Della Nossa’s foal
died last year from NI.

“Once a mare has had one foal with NI, there’s a high chance of recurrence, especially if she goes back to the same stallion,” says Lucy. “We couldn’t risk her foal drinking her colostrum this time, so we muzzled him at birth and bottlefed him another mare’s colostrum.

“We stripped colostrum from Della Nossa until we were sure that there was only milk coming out of all four quarters of her udder, which would not harm the foal.”

The process need not damage the mare-foal bond, adds Lucy.

“Stripping colostrum helps the mare produce oxytocin, the natural hormone that makes her protective
towards her foal,” she explains. “The foal is driven by instinct to suck, so he latched onto the bottle readily yet was still drawn to his mother’s udder. The minute the muzzle came off he nursed — and he hasn’t looked back since.”

Predicting a potential case of NI is possible by blood testing the mare in the last two weeks of pregnancy, but the most practical measure is close observation of the newborn.

“Be alert for a normal foal who suckles but then goes downhill,” says Lucy. “His gums and the membranes
under his eyelids should stay pink and moist, not pale or yellow. A weak, pale or jaundiced foal, perhaps  with a temperature or tremor, could well have NI and needs urgent veterinary attention.

“Once a foal becomes sick, it can be difficult to save him. Treatment needs to be aggressive and may be
expensive. Sadly, he could die in as little as 48 hours.”