Not sure who the bull is Farmboy ( what breed?)- but here is some information on DL's horse & the syndrome:
Of the top 15 halter horses in 1992, 13 were descendants of Impressive. Even at the age of 23, Impressive himself was fourth on the list. In 1993, it was estimated that more than 55,000 Quarter Horses, Paints, and Appaloosas world-wide bore his pedigree.
But what seemed like a winning streak to go down in history was soon to be overshadowed by tragedy. Greatness, unfortunately, was not the only thing that Impressive passed on. He has also been linked to a genetic mutation that only recently has been implicated in the rare but burgeoning - and sometimes fatal - muscular disorder known as hyperkalemic periodic paralysis. This particular defect is a dominant condition, meaning that at least half of the affected horses' offspring will be affected as well. In the words of one prominent Quarter Horse trainer, this discovery was "one of the most devastating things that has ever hit the horse industry."
Within a few years of Impressive's ascendancy to the top of the sire's list, halter horse owners began to notice a strange muscular twitching that often left their horses temporarily unable to move. Usually mis-diagnosed as tying-up syndrom or colic, these episodes varied widely in degree and duration....but all had one factor in common, their pedigree. As a result, many people now know HYPP as its' more common name: Impressive Syndrom.
Research funded by the AQHA and the University of California-Davis Equine Research Laboratory subsequently linked the problem to elevated levels of potassium in the blood serum. But even as researchers at leading veterinary schools began publishing articles in professional journals and trade publications, the vast majority of Quarter Horse owners remained unaware of the condition.
All the while, Impressive and his kin continued to make history.....breeding, showing, winning ribbons, and making their owners fantastic sums of money. Most affected horses can be controlled quite well with medication and a proper low-potassium diet, therefore, many owners of affected horses considered HYPP a minor inconvenience in light of the line's tremendous value. Given the fact that - at the time - there was no proof that the disorder was exclusive to the Impressive line - not to mention the fact that owners of stock descended from Impressive included some of the most prominent and wealthy individuals in the industry - no one wanted to be the first to publicly implicate the line. And, even later, when a breakthrough genetic test removed all doubt, lessening the moral and ethical burdens associated with naming Impressive as the carrier, neither the research community nor the AQHA was eager to lift the lid of this Pandora's box: Each feared possible legal and financial ramifications from a sector of the horse industry that would be shaken to its foundations.
In the past few years however, pressures both within and outside the Quarter Horse industry finally shattered the secrecy surrounding HYPP. The genetic test, made available in 1992, can identify affected horses with virtual certainty. As a result, many owners of horses descended from Impressive have rushed to have their horses tested, hoping that a negative result would protect their considerable investment against the anticipated backlash. Breeders have purchased advertising in The Quarter Horse Journal touting their HYPP-negative test results, and privately have urged their peers to either test their Impressive bred horses, or remove them from breeding.