Neonatal Isoerythrolysis in Foals

April 1, 2007 (published)

Today we are going to discuss a condition that develops in newborn foals that causes the destruction of their red blood cells. The condition is called neonatal isoerythrolysis and although that sounds like a confusing term, it simply means that the foal's red blood cells are being destroyed. The mare has antibodies that can damage the foal's red blood cells, and the antibodies are absorbed in the colostrum when the foal nurses. These antibodies then destroy the foal's red blood cells and cause anemia. These foals become weak usually in the first 1 to 4 days of life, and their mucous membranes become pale and then develop a yellow color called icterus.

If the problem is discovered before 24 hours of age, the foal must be stopped from nursing and fed an alternative food source. However, most of the time a foal is found to be sick after all the antibodies have already been ingested. Treatment of these foals sometimes requires a blood transfusion. Blood can by collected from the mare for transfusion, but it must be washed multiple times to remove the antibodies. Also, blood can be collected from another horse that is negative for the most common reactive blood types. It's a lot easier to prevent this syndrome than treat it. If a mare has had a foal develop this problem in the past, it is a possibility she could do so again. To determine if a future foal might be at risk for developing this condition, blood testing of the mare and stallion can be performed before the mare is even bred. Also, if the mare is already pregnant, the mare's blood can be tested for anti red blood cell antibodies by sending samples to the University of California at Davis.

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