Can Neurological Signs be Mimicked?

If a mare has a neurological disease, will the foal copycat her behavior? This veterinarian explains what happens to foals born to infected mares.

Q: If a mare with neurological problems gives birth, will the foal mimic her behavior? This is an ongoing debate at our barn. Some people are theorizing that as mom walks, baby walks, and as mom eats, baby eats. I understand that some foals, however, can be born with neurological diseases. Can you help us settle this?

Foals do not typically mimic neurological quirks of their dam, unless they themselves are affected by the disorder.

A: Although it is true that foals sometimes mimic the behavioral patterns of their mothers, those born to mares with neurological issues generally do not imitate those deficits. At our neonatal intensive care unit, we have delivered many foals from mares who were afflicted with equine protozoal myeloencephalitis (EPM), one of the more common infectious neurological diseases seen in horses. These foals do not display any of the neurological signs their mothers do.

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However, foals can be born infected with organisms that cause neurological disease that are passed down from the mother. For example, studies show that one of the organisms that can cause EPM, Neospora hughesi, can be transmitted via the placenta to the fetus carried by some naturally infected mares; however, the foals who were found to be infected with the protozoa did not necessarily demonstrate neurological signs for up to three months after birth. Likewise, transmission of the highly contagious equine herpesvirus type-1 (EHV-1) can also occur from the dam to the fetus via the placenta, but while these foals are born with EHV-1 in their bloodstream and various organs (lungs, liver, thymus), the majority of them do not show any neurological signs.

The most common cause of neurological disease seen in the newborn foal is neonatal encephalopathy. This can occur when the fetus is deprived of oxygen in the womb because the placenta is not functioning properly, usually because of a bacterial infection (placentitis). In cases like these, the foals are born with neurological abnormalities, such as incoordination and lack of the suckle reflex. Neonatal encephalopathy may also develop in foals who are deprived of oxygen for too long during the birthing process, as we often see with difficult deliveries (dystocias); these foals generally do not develop neurological signs for up to 18 to 24 hours. In both scenarios, the lack of oxygen leads to fluid accumulation in the brain tissue (cerebral edema), and damage may also occur to other organ systems, such as the kidneys and gastrointestinal tract. The prognosis for these foals is generally very good if they are treated early and appropriately.

Rodney L. Belgrave, DVM, DACVIM
Director of Internal Medicine
Mid-Atlantic Equine Medical Center
Ringoes, New Jersey

This article first appeared in EQUUS issue #427.

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