General Discussion
In reply to the discussion: We’re Breeding Dogs to Death [View all]csziggy
(34,136 posts)I don't know if you are familiar with that line of Quarter horses, but Impressive was a stallion who produced a lot of foals that did well at mostly halter classes. I never liked the horses from that line - they were weak in the loin, strung out, and could not move well from my observations. Most did well only as halter horses and were not known for winning performance or working classes. I was criticized for not buying some broodmares from that line and turning down free breedings from a stallion owner who was trying to promote his Impressive grandson. The horses just were not what I wanted to produce.
Later, it was found that that line carried a gene that causes a "condition known as hyperkalemic periodic paralysis (HYPP). This condition is characterized by intermittent episodes of muscle tremors (shaking or trembling, weaknesses and/or collapse)." http://www.aqha.com/About/Content-Pages/About-the-Association/Services/HYPP.aspx It is a defect in the sodium channel that carries minerals through the cell walls. Imbalance of the minerals cause the tremors because the muscles do not have the proper levels of minerals to function.
So many Impressive descendants were being sold to unsuspecting buyers AQHA eventually had to start DNA testing of all AQHA horses to inform people and remove the stigma from the breed. When they first began the testing they did not release the name of the KNOWN stallion with which the genetic defect originated. It took years before AQHA finally acknowledged what most Quarter horse people knew.
AQHA still will not eliminate that line from their books - they do require genetic testing so owners and buyers are aware. But breeding the horses that test positive - whether hetreozygous or homozygous - is not prohibited so the association is still allowing production of a trait which causes agony for some horses and death for others. The other two genetic traits that AQHA tracks and limits, Parrot Mouth and Cryptorchid conditions, are not fatal, just undesirable. (Parrot mouth is an overbite and causes problems with eating a nutrition; Cryptorchid is retained testicles which make it expensive to neuter and impossible to verify that the horse has been neutered completely - since the horse may still be fertile {though chances are reduced} and still produces male hormones, this affects the horse's personality and usefulness.)