Many people are under the impression that grade horses (those whose parentage is unknown, unidentifiable, or of significantly mixed breeding) are largely to blame for the horse overpopulation issue. The May 2010 issue of The Horse had a letter to the editor that again stated horse overpopulation would be reduced if people stopped breeding grade horses.

Grade horses provide a great pool of genetic variation and generally lack many of the genetic diseases that currently can afflict purebreds. Their lack of papers does not decrease their functionality, with the exception of not being able to show at breed-specific events. Papers increase a horse's value only by showing potential based on parentage. Papers do not prove an animal is sound physically or mentally, free of genetic illness, or capable of performing well. Grade horses that sell do so based on their own merits of soundness and functionality.

grade horse

Regardless of whether a horse is grade or purebred, it’s the owner’s responsibility to breed for a sound, disease-free animal.

In purebreds, as you continually select a specific trait or breed type, you diminish the amount of genetic variation within that breed. When this is done, genetic problems, which nature previously reduced through genetic variation, can become focused. Many species of animals that humans breed for specific characteristics develop genetic diseases. In many cases these diseases have decimated breeding populations of purebreds. Foundation breeds may not be available to "restart" the breed.

An example of disease related to the purebred horse industry is HYPP (hyperkalemic periodic paralysis) in the Quarter Horse. Arabians have six genetic illnesses currently in their lines; lavender foal syndrome and severe combined immunodeficiency (SCID) are two. Belgian draft horses can carry genes for junctional epidermolysis bullosa (JEB), a disease that causes skin lesions over pressure points of the body. This is not an all-inclusive list of disease-prone breeds--these are just a few breeds currently popular in the United States.

Owners of purebred horses subject to genetic disease who don’t know if their animals are carriers should spend the money for genetic testing. To reduce the frequency of the disease, those animals that test positive should then not be bred. Many owners don't test; others might test their animal and, if he tests positive, will still breed, but only to other individuals that test negative. This does not eliminate the trait but, rather, dilutes it, and the disease can reappear with more animals ­affected.

In addition to genetic disease, some purebred horses have problems carrying foals to term. Studies have been done to determine how much estrogen must be given to a mare, unable to maintain a pregnancy on her own, to obtain a foal. Continuing to breed these horses has the potential to develop a horse incapable of producing a foal without human intervention and hormone therapy.

Anyone breeding a horse, be it grade or purebred, mare or stallion, is responsible to breed for a quality animal. Horse ­overpopulation won't be solved just by castrating stallions. Mare owners carry as much responsibility as stallion owners to evaluate quality and remove animals with unsoundness or genetic disease from the breeding population. One stallion, purebred or grade, can sire many foals, but only if the mares are bred to him. If multiple foals from a stallion have crooked legs, then you should not be using that stallion. Horses with poor feet or other unsoundness issues shouldn’t be bred, regardless of the financial value of the horse on paper.

Consider the canine mutt, often one of the longest-living and healthiest dogs around (G. J. Patronek, et al., 1996). I don't know if research has been done with horses to determine the longevity of grade horses versus purebred, but if you compared longevity and health I believe you would find the same trend with grade horses as we find in our canine mutts.

Yes, we have a horse overpopulation problem that needs to be dealt with. But do not attack every breeder of grade horses. "Grade horse" does not mean poor quality. Likewise, purebred and papered does not prove good quality. Keeping a population of crossbred and grade horses is a healthy means of maintaining the genetic variability of the horse population as a whole.

Reprinted from the August 2010 issue.


Marla Trowbridge, MS, is a former veterinary technician and researcher at Utah State University, where she worked with genetic disease in Suffolk sheep. She currently lives in Trenton, Utah, and owns eight horses, four of which are grade horses.