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Immune-deficiency Diseases in Horses


Ian Rodney Tizard

, BVMS, BSc, PhD, DSc (Hons), DACVM, Department of Veterinary Pathobiology, College of Veterinary and Biomedical Sciences, Texas A&M University

Reviewed/Revised Mar 2019 | Modified Oct 2022
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Immune-deficiency diseases have serious consequences and often lower the body’s defenses against infection. Some are inherited, and others are caused by viral infections or cancer.

Immunoglobulin Deficiency

This condition is due to a failure of the body to produce antibodies (immunoglobulins). The deficiency can be acquired (caused by other diseases) or congenital (present at birth). Congenital antibody deficiencies can occur alone or as part of combined immunodeficiency (see below). Older foals born with this deficiency often develop respiratory infections.

Acquired deficiencies occur in foals that do not receive adequate maternal antibodies from the colostrum produced by the dam during the first several hours of nursing. This is also called failure of passive transfer. It can occur when a newborn foal fails to nurse properly, when the mare's colostrum contains low levels of certain antibodies, or when the antibodies are not absorbed properly from the digestive tract. Newborn animals that do not obtain adequate levels of these antibodies often develop fatal bacterial or viral infections of the gastrointestinal or respiratory tract.

It is important to ensure that newborn foals receive appropriate amounts of colostrum, preferably within the first 30 to 90 minutes after birth. Your veterinarian can measure the level and, if it is low, may recommend providing colostrum from another mare or from a frozen supply.

Foal nursing

Foal nursing

Some foals have temporary antibody deficiencies. Affected foals frequently develop respiratory infections around 6 months of age (when antibody levels from the mother become low). Supportive treatments and antibiotics are often necessary until they begin to produce antibodies on their own, usually when they are 9 to 11 months of age.

Immunoglobulin deficiency can occur as part of any disease that disrupts the production of antibodies in the body. For example, certain tumors (such as lymphosarcoma and plasma cell myeloma) cause the production of abnormal antibodies, which decreases production of normal antibodies. Affected horses can develop severe infections due to the deficiency. Depending on whether the deficiency is short- or longterm, treatment with antibiotics and intravenous immunoglobulins may be needed.

Combined Immunodeficiency Disease

Combined immunodeficiency disease involves a defect in both cell-mediated immunity and antibody production. This inherited disease has been seen in Arabian foals in which the thymus (the organ that produces certain immune cells) is abnormal. Affected foals lack both T and B cells, which makes it impossible for the body to fight foreign invaders. The foals are healthy during the first several months of life but become progressively more susceptible to bacterial infections as the antibodies they received during nursing disappear. They tend to die from pneumonia or other infections, frequently by 2 months of age. No treatment is available. Testing is available to detect the disorder in foals and the abnormal gene in breeding animals. As a result of this testing, the prevalence of the disease has declined significantly.

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