Much like HYPP in the QH industry(I also raise QH's) or the Stress Gene in the showpig industry, TH and PHA themselves bring nothing to the industry. The problem is that a lot of animals that carry traits that we really like, also carry these genetic issues. I have personally never owned a horse that I knew carried HYPP or a cow that I have been aware of was a carrier of TH/PHA. But I have owned market barrows that were stress positive and sows that were carriers. My absolute rule has always been that I would not even consider breeding a carrier to a carrier. If I own a carrier it has to be one absolutely great specimen, if not it goes to the sale barn. There is no way, regardless of how good that I would ever breed something that carried any of these recessive traits in the homozygous state. And if I do decide that a carrier is good enough to breed they will absolutely be bred to something that I know for a fact is completely clean of the trait.
The problem comes that the positive traits that accompanies these negative traits are so desirable that people are willing to risk the negative to get the positive so they continue to breed them. There are many who think all the heaviest muscle clubbies will at least be carriers. But I remember a time when the same thought went with HYPP and Stress, the heaviest muscled ones were carriers. But over time, testing, and selective breeding, there are HYPP negative horses with as much muscle as the HYPP carriers/positives and there are Stress Free pigs with as much muscle as the carriers/positives. While many breed associations will not register true positive animals, most all will register carriers, but the problem comes that we cant regulate the crosses. In the QH and Pig worlds education and clean breeding options have helped a lot. While we havent completely irradicated the issue, it is much less severe than it once was. I can only hope that the same thing happens soon in the cattle world.
