by Anna Hiatt, HEHC Veterinary Assistant Intern

Breeding horses is not a simple subject. Aside from finding a suitable sire and dam, certain requirements must be met such as space and available funds. Even a use for the horse must be considered when planning for a foal. There is a hidden requirement, however. The genetics of a horse play as much of a part in the breeding process as anything else. Without proper DNA testing, owners can create lethal crosses resulting in an early death for the foal.

Through genetics, a horse can carry a defective gene without showing any signs of sickness. When a foal is conceived, it receives two copies of each gene; one from their father, and one from their mother. A horse may carry a mutated version of a gene, however, and pass it onto their offspring. Thankfully, most genetic disorders are recessive, meaning that the foal needs two copies of a defective gene for any problems to arise. Still, tests must be conducted before breeding to ensure the safety of the foal. Listed below are some common lethal disorders that different breeds can carry. All can be tested for, but there is no cure for these deadly disorders.

Arabians: Lavender Foal Syndrome, or LFS, is apparent particularly in “Egyptian” lines of Arabians. Foals will be born with a diluted color of coat and will not stand, and often experience seizures. Severe Combined Immunodeficiency (SCID) is also a concern, as a foal never develops its own antibodies aside from the ones received from the mother. Thus, it has no immunity to infections later in life. This will present possibly up to 5 months after birth, since foals with this condition appear normal at first due to antibodies provided by the dam’s first milk.

Paints: Overo Lethal White Syndrome is a large concern among breeders. Non-afflicted horses will usually have solid darker coat colors, and carriers will be mostly white overo Paints. In crossing two carriers together, a white foal with blue eyes can be born. It will appear normal at first, but will then colic within the first few days of life as it is unable to pass feces due to the colon ending in a blind end. Not all overos carry this gene, however. Most issues seem to be with the frame overo pattern.

Draft and Saddlebreds: Both of these breeds can carry different variations of junctional epidermolysis bullosa, otherwise known as Red Foot Disease due to foals often sloughing off their hooves. Foals born with this condition lack the protein to bind their epidermis (outer skin) to their dermis (deep skin), and any form of slight trauma will cause the skin to slough and ulcerate.

Fell and Dales Ponies, Gypsy breeds: Foal Immunodeficiency Syndrome is present in these rare breeds. Foals born with this condition suffer progressive anemia, anorexia, diarrhea, and nasal discharge. Sadly, there is no cure for this disease and treatment is unsuccessful, unlike in humans afflicted with this disorder.