Neonatal Isoerythrolysis: An Ounce of Prevention
Dr. J. Barry David, Diplomate ACVIM, Specialist in Internal Medicine
Dr. Krista Estell, DVM
Ms. Hope Connelly, Laboratory Supervisor
Neonatal Isoerythrolysis (NI) is an immunologic disease which affects approximately 1% of Thoroughbred and 2% of Standardbred foals each year. NI occurs when the mare has produced antibodies that are directed against her foal’s red blood cells and the foal nurses and absorbs this colostrum. These mare generated antibodies destroy the foal’s red blood cells and result in anemia. The severity of clinical signs depends on the amount and strength of the antibody absorbed by the foal and the degree of anemia produced. Affected foals are normal when they are born and then develop clinical signs within 5 hours to 5 days after birth. Clinical signs include lethargy, depression, an increased heart rate, an increased respiratory rate, a yellow (jaundice) tinge to the eyes and gums, and dark colored urine. Severely affected foals may go into hemodynamic shock, have seizures and die due to the lack of red blood cells available to carry oxygen to the brain and other vital organs.
In peracute cases the foal may die before the disease is recognized, whereas foals with slowly progressive signs often live with appropriate supportive care. Depending on the age of the foal when neonatal isoerythrolysis is diagnosed, the foal should be muzzled for approximately 48 hours and fed an appropriate milk replacer. During this time the mare should be milked every 2 hours and the milk then discarded. Additional treatments will be dictated by the severity of the foal’s condition at the time a diagnosis is rendered. Other therapies may include: admission to an equine referral hospital, anti-inflammatory agents (+/- corticosteroids), IV fluids, and supplemental oxygen. Severely affected foals may require a blood transfusion from either washed red blood cells from the foal’s mare or blood from a suitably cross-matched blood donor. If a diagnosis of NI is made early, the majority of these cases are discharged from the hospital after 5-7 days of therapy.
Like most diseases, NI is much more easily prevented than treated. Your index of suspicion should be high for any mare that has produced an NI foal previously. Fortunately for mares that have not produced an NI foal previously, there is a simple blood test that can identify “at risk” mares before the foal is born. Collect 6 mls of blood into a red top tube from your foaling mares within 14 – 21 days of foaling and submit the blood to an approved laboratory. The test detects the presence of anti-red blood cell antibodies in your mare’s blood. If the NI blood screening test is positive, your foal should be muzzled immediately after it is born and you should call your veterinarian.
The laboratory at the Equine Medical Center of Ocala is one of few laboratories in the Southeast United States that performs the screening test for NI. If you have additional questions regarding NI as a disease, please contact Dr. J. Barry David at the Equine Medical Center of Ocala at 352.479.0480. If you have questions regarding the specific days that our laboratory run the test, submission requirements (blood tube type, volume required, cost) please contact Hope Connelly at 352.840.0965.