“We try to focus genetic research on traits that are of greatest economic value,” said Samantha Brooks, who has a PhD in veterinary science.
In this podcast episode, we talk about topics from coat color (which also has deadly health ramifications), to genetics that link height of horse and health issues, to how genes react to virus such as those that cause sarcoids.
Coat color
While coat color is extremely important to some breeds, there also can be genes that affect coat color that affect the health of the horse. One example of this is lethal ovaro coat syndrome. “One copy of the gene gives a beautiful spotting pattern,” said Brooks. “Two copies of the gene mean the foal is born entirely white and the GI tract doesn’t work. If the fetus survives to birth, the foal won’t survive.”
There are natural mutations that are not linked to health issues, such as white and paint-colored Thoroughbreds.
Height and roaring
An individual inherits two alleles, one from each parent, for any given genomic location.
There are five genes that affect height of a horse. “Pony breeds have genes that select to short height,” said Brooks, and draft breeds have genes that select for larger horses.
However, research has shown that the same allele(s) that contributes to height also could affect roaring (laryngeal hemiplegia, where the larynx is unable to move properly and doesn’t move out of the airway and can interfere with air flow).
Other research has linked OCD in joints to a genetic risk. And still other research has shown that Thoroughbreds with longer limbs/shoulders equaled increased earnings.
“So, a horse that is taller can win more, but has an increased risk of RLN and OCD,” noted Brooks. “Now what do we do?”
She said genetic testing might help owners know what risks a horse has and could advise a better breeding to gain the desired traits while avoiding the undesired problems.
Genetics and sarcoids
We know sarcoids in horses are caused by viruses. However, there are genetic influences that tell the body how to react to viruses, noted Brooks.
Genetics and anhidrosis
Horses and humans sweat to thermoregulate. There are no treatments for horses with anhidrosis (inability to sweat). The only way to help these horses is to move them to areas that have low heat and humidity.
Research has shown that there could be genetic triggers for anhidrosis. If this turns out to be true, “there are lots of human drugs that might be able to treat this disease in horses,” noted Brooks.
Neurologic and metabolic genetics
Some horse breeders don’t want to test for potential genetic problems because of the marketability of horses that have specific genetics.
“Genetics can be used for culling and strategic breeding,” noted Brooks. “That’s important. Some of these [genetic] issues can be deadly.
“Breeders should think of genetic testing as an investment for management,” she said. “That’s a big responsibility of breeders and horse owners.”
About Dr. Brooks
Brooks is an Associate Professor of Equine Physiology in the Department of Animal Sciences at the University of Florida. Her research program explores a variety of topics relevant to horse health ranging from gene expression studies to mapping of genetic disorders in the horse. Previously her research group discovered genetic mutations and markers for coat colors, height, sarcoid tumors and two neurological conditions. Ongoing work targets variation in gait, susceptibility to infectious disease, metabolic syndrome and skeletal defects using genome wide association and genome re-sequencing.
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