January 2021 - Horse Breeding Issues: Jaundice Foal Syndrome
Written by courtesy of America’s Horse Daily
Friday, 01 January 2021 19:57
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courtesy of America’s Horse Daily

Early foaling begins soon. With the arrival of January foals just around the corner, now is the ideal time to blood-type mares to estimate the probability that your baby will develop jaundice foal syndrome. As with many other conditions, prevention and early recognition is the best remedy.

Neonatal isoerythrolysis or jaundice foal syndrome is an uncommon but potentially life-threatening condition of newborn foals. It has been estimated to occur in 1 to 2 percent of equine births.

The condition occurs when a foal ingests colostrum containing antibodies directed against its red blood cells. Destruction of red blood cells releases pigment called bilirubin that may cause the gums, white parts of the eye and feces to become yellow or jaundiced.

What Happens

Horses have a number of blood groups, the most common of which are Aa and Qa.

A foal can inherit its blood group type from either the mare or the stallion. If the stallion and mare have the same blood group, the jaundice problem cannot occur. If a foal inherits the blood group type of its dam, there will also be no chance of developing this syndrome.

The condition occurs only when the blood group of the foal is different than that of the mare because it was inherited from the stallion and is different than the dam’s blood group.

Exposure of the mare during pregnancy or at foaling to red blood cell antigens (blood group types) other than her own will cause her immune system to begin developing antibodies against the “foreign” red blood cells.

Typically, limited antibodies are produced during the first exposure to a foreign red blood cell group, so the syndrome is rare in maiden mares.

However, if the mare is exposed a second time, a far greater quantity of antibodies may be produced. The antibodies are concentrated in the colostrum during the last two to three weeks of pregnancy.

In most instances the presence of anti-red blood cell antibodies in the mare goes unnoticed, and the foal is allowed to nurse colostrum from its dam. Antibodies are absorbed into the blood stream of the foal, where they attack the foal’s red blood cells.

Affected foals usually begin to show clinical signs between 24 and 72 hours of life. Signs may include jaundice, weakness, lethargy, decreased nursing vigor, increased respiratory and heart rate, recumbency, passage of red-colored urine and possibly death.


Treatment of affected foals may involve one of more blood transfusions from a cross-matched donor horse or washed red blood cells from the mare.

Additional therapy can include purified hemoglobin, antibiotics and other medications.

In theory, the disease can be prevented by blood-typing the mare and prospective stallion(s) and avoiding breeding a mare without the blood groups Aa or Qa to a stallion with those blood groups. However, this is not very practical.

It is far easier to test the blood of broodmares in the last few weeks of gestation for antibodies against the common red blood cell antigens.

If no potentially offending antibodies are detected, the risk of jaundice foal syndrome is extremely low. However, if antibodies against one or more red blood cell antigens are present in the blood of the mare, the foal could be at risk of developing the syndrome if allowed to nurse colostrum from the mare. The screening test is available through several diagnostic laboratories around the country.

If a mare has had a foal affected by the syndrome in the past, or if she is found to have antibodies in her blood against other equine blood groups, the newborn foal should not be allowed to nurse from her and should be provided colostrum or antibodies from a safe source.

The foal can be muzzled to prevent nursing and yet still allowed to remain with the mare. The colostrum of the mare should be stripped out every few hours and discarded. After approximately 36 hours, the mammary gland of the mare will no longer be producing colostrum and the foal can no longer absorb antibodies if they were present. The muzzle can then be safely removed and the foal allowed to nurse from the dam. It is critical that initially colostrum and then later on an alternative nutrition supply be provided to the foal during the 36-hour period.