Neonatal isoerythrolysis: When mare’s milk can kill

Read more: Reuse: You may use up to 20 words and link back to this page. Other reuse not permitted Follow us: @HorsetalkNZ on Twitter | Horsetalk on Facebook  Hannibal was allowed to stay in the same stall as his mother to help promote maternal bonding, but for 24 hours had to wear a foal-size leather muzzle to prevent him from suckling.
Hannibal was allowed to stay in the same stall as his mother to help promote maternal bonding, but for 24 hours had to wear a foal-size leather muzzle to prevent him from suckling.

Hannibal was keen to drink his mother’s milk, but veterinarians knew her colostrum could potentially kill him.

For that reason, he spent the first 24 hours of his life in a leather muzzle – hence his name.

The muzzle came off for regular feeds with more suitable milk from another mare, while his mother’s milk was taken from her every hour and discarded before Hannibal was able to safely suckle after 24 hours.

Mother’s milk is almost always best for the baby, especially when that baby has four legs, weighs about 45 kilograms and is born hungry. However, in some equine cases, a mother’s milk can be toxic and lead to severe illness and, if untreated, even death.

Hannibal was spared this fate because veterinarians at the Colorado State University Equine Reproduction Laboratory used a simple test to find out if he was at risk.

Neonatal isoerythrolysis (NI), also known as jaundice foal syndrome, is a rare disease that may occur in a foal if the mother has antibodies against the red blood cell type of the newborn foal.

Foals are normal at birth and are affected only if they ingest colostrum with anti-RBC antibodies directed against their own red blood cells.

If the foal has the same blood type as its mother, there is not a problem.

NI occurs if the foal inherits the blood type of its father and if the mare’s antibodies are directed against that specific blood type.

These antibodies are sequestered into colostrum, the first “mother’s milk” the foal will suckle. Exposure to these antibodies puts susceptible foals at risk.

“A blood sample from Hannibal’s mum showed a strong positive reaction for antibodies against Aa blood group antigens,” said Dr Patrick McCue, an equine reproduction specialist at the Veterinary Teaching Hospital and Equine Reproduction Laboratory.

“The immune system of the mare must have been exposed to ‘foreign’ red blood cell antigens by leakage across the placenta during a previous pregnancy or foaling.”

During the first 24 hours of life, the gut of a foal absorbs antibodies from the mare’s colostrum after nursing.

Ingestion of colostrum is critical for the health of the foal as foals are not born with antibodies in their blood that will protect them from various infectious disease organisms they will encounter after they are born.

Foals and other large animal newborns are dependent on antibodies from their mother that they obtain through colostrum; a process called passive transfer of immunity.

However, if a foal ingests colostrum containing antibodies against its blood type its red blood cells can be damaged or destroyed, leading to anemia.

“In Hannibal’s case, we collected a blood sample from him immediately after birth and performed a jaundice foal agglutination test using his blood and colostrum from the mare,” McCue said.

“The test indicated a positive reaction; therefore, the foal could not safely ingest colostrum from his own mother.”

NI-affected foals usually begin to show clinical signs, such as jaundice, weakness, increased respiratory rate, and passage of red-colored urine within 24 to 72 hours after taking in ‘toxic’ colostrum.

Severely affected foals may die if untreated.

Hannibal was allowed to stay in the same stall as his mother, to help promote maternal bonding, but for 24 hours had to wear a foal-size leather muzzle to prevent him from suckling.

His mother’s colostrum was hand-milked and discarded every hour.

Meanwhile, Hannibal received colostrum that had been harvested from another mare that was known to be free of the anti-RBC antibodies.

The alternative colostrum provided the immune protection he would need to survive until his own immune system produced antibodies. He was also bottle fed a commercial mare milk replacer until he was allowed to nurse from his mother.

“After 24 hours, the mare did not have any more colostrum and Hannibal was no longer at any risk,” said McCue.

“Fortunately, the mare’s maternal instincts were strong and Hannibal eagerly suckled once his muzzle was removed. A healthy Hannibal and his mom went home five days after foaling.”

McCue said the take-home message for horse owners is that neonatal isoerythrolysis is a life-threatening condition of newborn foals. It can be prevented by a pre-foaling screening of the mare’s blood and, when a potential problem is detected, screening of the foal to determine if its mother’s first milk – exquisitely designed to protect the foal from infectious disease – is a lifesaver or threat to its health.

First published on in July, 2011

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One thought on “Neonatal isoerythrolysis: When mare’s milk can kill

  • August 4, 2019 at 1:35 am

    I had foal he was month old doing.good couldn’t.afford feed a bunch of horses anymore so gave to rescue 6 weeks later baby got sick diarrhea bad lost weight lady took to vet 3days later 2weeks after he passed away.I guess they couldn’t figure it out I thought maybe colic but not bound up theatre moms milk since she had baby’s before him one every year for 3years they were fine


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