Neonatal isoerythrolysis (NI) is a condition in where the mare produces antibodies concerning her foal’s red blood cells (RBC). The foal consumes these antibodies in the mare’s colostrum as it nurses. These antibodies cause clumping and rapid destruction of the foal’s red blood cells. Neonatal isoerythrolysis is an immunological ailment that characteristically affects foals between 1 and 7 days of age. Neonatal isoerythrolysis is an
…acquired form of immune-mediated hemolytic anemia, resulting from a blood-type incompatibility of the mare and foal. (Bailey)
This ailment is quite rare, with an estimated 14% of foals having “…erythrocyte incompatibilities with the dam (Polkes).” However, the prevalence of the ailment is only 1-2%, with some breeds reporting a higher frequency (Bailey).
There are numerous explanations as to why this ailment transpires. One of these explanations is that these antibodies form due to the mare being exposed to foreign red blood cells. This occurs for a plethora of reasons, including if: the individual receives a whole-blood transfusion or other blood products, vaccines containing equine tissue or if a mare is exposed to foetal blood during a previous pregnancy. (Finding)
Common reasons for the mixing of the mare’s and foal’s blood include a placental hemorrhage at parturition. If the mare happens to be carrying a foal with different red blood cell antigens than hers and their blood mixes then her body produces antibodies against the foal’s red blood cells in order to safeguard her from the threat. However, while the foal is in utero, it is unaffected; due to there being no mixing of the blood. (Finding)
Strangely enough, foals from maiden mares are rarely diagnosed with neonatal isoerythrolysis. Thi...
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...outcome. In a study done by A.C. Polkes, et. al, they found out that out of 72 foals, the survivors were admitted with an average temperature of 101.8 °F. Other factors include: respiratory rate, heart rate, age, and RBC level (Polkes).
The prevention of this disease is to identify the mares that are predisposed to causing RBC destruction in foals. One way to test for this is to blood-type mares before their first breeding. This lets the owner/breeder find both mares and stallions that are negative for blood antigens to breed together. However, in rare instances blood –typing will not successfully identify mares that have hemolytic antibodies (Bailey). Mares with unknown blood-types can also be tested for the antibodies before the predicted due-date; if this test comes back positive then the foal must be removed immediately until the mare stops producing colostrum.