GENETIC ROULETTE - CHANCE OR CHOICE?

By: Kathy St.Martin
(First appeared January/February 1997, Hunter & Sporthorse Magazine)

Throughout the ages, human arrogance and vanity have caused countless problems in society. Generations of medieval monarchs and aristocrats married only within their limited class at the top of the social heap. Whether for political expediency or eventually for tradition, they married cousins, sisters, brothers, daughters, etc. The final result of these countless unions within a small group, resulted in idiocy, genetic diseases (e.g. hemophilia, cleft palates, mongolism) and a general declining ability and intelligence of the individuals involved. Is it any surprise then, that humans should impose these same standards on other endeavors? Our interest here, in particular is the lack of adequate criteria to select animals worthy of reproduction.

When man intervenes in the genetic selection of animals, he opens doors for many kinds of mutations upon the particular breed or species he chooses to "manipulate". Since many naturally occurring mutations are lethal in the wild, the resulting mutants (also known as "sports") rarely, if ever, manage to reach maturity and thereby obtain the opportunity to reproduce. However, when man intervenes, the chances of an animal with a genetic defect reaching maturity and thereby reproducing, increases dramatically. Albinos, for example, are rarely seen in the wild inasmuch as they are highly visible to predators. Their eyesight is generally poorer and they are unable to resist the effects of the suns ultraviolet rays as well as their pigmented counterparts. When albinism occurs in captivity, the likelihood of survival increases exponentially and thereby, their chances of reproducing offspring like themselves.

In an attempt to obtain desirable characteristics more quickly, we have often resorted to in-breeding or line-breeding to create a smaller gene pool. With a smaller pool, the opportunity to "match" genes is greatly heightened. Unfortunately, in an attempt to match genes and maximize desirable traits, you also maximize the opportunity to match undesirable traits as well.

With the American horse industry being as open as it is, restricting breeders from allowing animals with negative genetic traits to reproduce is difficult. An example of this is the Quarter Horse industry which is currently struggling with the hyperkalemic periodic paralysis (HYPP) scandal and shows little progress in moving towards any definite resolution. The gene is traceable to a specific Quarter Horse stallion, Impressive, and as there is a test currently available, breeders have the option of testing their animals for the gene. However, many stallion owners, rather than risk losing bookings, do not disclose positive results of tests or don't have their stallions tested at all. The flip side of the coin is the mare can also be a carrier of the gene, so they need to be tested as well. Not surprisingly, with the massive amount of information presented to the horse oriented public, Impressive bred horses have become less marketable. Consequently, owners are reluctant to use Impressive bred individuals, especially HYPP positive animals.

The current brouhaha over the Impressive line, and more specifically, (HYPP) carrying horses in the Quarter Horse industry is probably one of the most publicized and controversial of any equine related problem in some time. Quarter Horses are are not the only breed to have been plagued with genetic problems. Arabians, Saddlebreds, Morgans, Thoroughbreds, and Paints, all have skeltons in their genetic closets. How we as humans deal with the issue is, to a large part, the basis of the controversy.

The Arabian industry fell victim to a similar problem in which combined immunodeficiency (CID) is suspected to be traceable back to a particular group of animals. Unfortunately, it wasn't until recently that efforts were made to publicly disclose those animals which are known carriers. It is estimated that as many as 30% of the registered stock are now carriers. Fred Metcalf, Chairman of the recently formed Fighting Off Arabian Lethals (FOAL) Commission of the International Arabian Horse Association stated that breeders of Arabians are overwhelmingly supportive of disclosure of CID carriers. He is hopeful that with the revealing of known carriers, a common denominator can be determined. By knowing which particular bloodlines the gene originated from, breeders will then be able to make informed decisions on how best to proceed with their breeding programs. Lance Perryman, DVM, PHD, formerly of Washington State University (home of the largest CID carrier herd) and one of the leading researchers of CID, stated that although there is no test available to date, he is optimistic that one will someday be developed. To date, the only way to discover which animals are carriers is when a foal is born with CID (this will occur in approximately 25% of the matings of two CID carrier parents). When a CID foal is born, you know both parents are carriers of the particular gene and should no longer be allowed to reproduce.

In the Paint industry, the dilemma is "Lethal White" in which foals die, usually within hours of birth . The problem is usually associated with mating overo to overo. By avoiding the crossing of this color pattern, you minimize the chance of producing a foal that is destined to die shortly after birth. When horses with this particular color pattern are crossed, they have a higher likelihood of producing "color". Unfortunately, many breeders still pursue this crossing as they believe the greater probability of producing that colored foal outweighs the risks involved.

So, how does the horse industry regulate itself? With registries reluctant to impose any kind of restrictions upon breeders, it doesn't. Also, as most breed registries are "closed", breeders are required to pick from animals within the registry and thereby are again limited to a specific gene pool.

In a recent interview with Ekkehard Brysch of the Oldenburg Verband/International Sporthorse Registry, the subject of genetically unsound horses was discussed. I asked him how he would attempt to control such a problem, if it ever arose, to minimize the impact upon the rest of the breed. His solution was to require all currently approved stallions to disclose the results of a test (if one were available), with the results being published in the current year's Breeders Guide. Owners who did not have their stallions tested or who did not wish to disclose the results, would have a notation on the information page of their stallion. Any young stallion requesting certification or approval would be tested and a negative result would be required before being allowed to receive a breeding license. By publicizing results and requiring negative test results for newly approved stallions, the impact would be minimized. Also, as the Oldenburg Verband/ISR is an "open" registry, there is always the opportunity for new blood and the chances of undesirable genes being matched is considerably less.

In the United States, our philosophy has been to avoid interfering or placing restrictions on individuals. Hopefully, most people will do what is correct when faced with a moral or ethical choice, but there are always a few individuals who believe they have the "right" to do as they wish. Without any kind of restrictions, guides or controls, it is up to the individual breeder to make a decision which will not perpetuate a problem. The final product will ultimately be the breeder's responsibility. Optimal breeding of horses will always be a slow and arduous process. Attempts to take short cuts will not always produce the desired effect. Indeed, as discussed above, there are many genetic pitfalls into which a breeder can fall. Making a decision which is morally and ethically correct will ultimately be the most rewarding for all concerned. Allowing animals with known genetic disorders to reproduce perpetuates a problem which can only lead to disappointment. It is to be hoped that more breeders will take the ethical and moral "higher ground" and choose to follow a path that will produce not only genetically sound offspring, but financial profits as well.

A special thank you to Dr. Lance Perryman, D.V.M., PhD, North Carolina State University College of Veterinary Medicine; Ekkehard Brysch, Oldenburg Verband/International Sporthorse Registry; Fred Metcalf, Fighting Off Arabian Lethals (FOAL) Commission, International Arabian Horse Association; and Dr. James Noone, D.V.M, Town and Country Animal Hospital, Gunnison, Colorado.


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