Concerns about Salix’s performance-enhancing attributes may pale in comparison to the potential detrimental effects the drug’s widespread use in North America may have on the genetic health of the Thoroughbred.
The heritability of exercise-induced pulmonary hemorrhaging, commonly known as bleeding, came to light during a veterinarian panel discussion as part of the public session of the two-day International Summit on Race Day Medication, EIPH and the Racehorse at Belmont Park.
South African-based international veterinarian John McVeigh said the genetic connection of EIPH was made in a study done by Hans Weideman, S.J. Schoeman, and G.F. Jordaan and published in the South African Journal of Animal Science in 2004. The study is called “A genetic analysis of epistaxis as associated with EIPH in the Southern African Thoroughbred.”
“The relationship between runners with EIPH and the stallion has a heritability of 0.4, which is very high,” McVeigh said during the panel discussion. “The two sires that produced the most bleeder progeny were both champion sires.”
How the South African study relates to Salix being used in the U.S. is that more American stallions are being exported to South Africa and the average number of bleeders per runners is increasing in South Africa, according to McVeigh. With Salix being used largely as a preventative in the U.S. and used in at least 90% of runners, there is no reliable tracking of which horses actually have significant cases of EIPH. Race-day use of Salix is banned in South Africa and all bleeding cases are carefully monitored. For example, all horses are walked around a paddock ring for five minutes following a race so veterinarians inspect for any signs of bleeding.
“The conclusions (of the study) were very strong,” McVeigh said.
The study looked at pedigree and race data from Thoroughbreds racing in Southern Africa from 1986 through 2002. There were 63,146 horses in pedigree data-set and the results of 778,532 races were analyzed. The variables accounted for included age, weight, altitude, sex, month and track condition.
“The heritability estimates...epistaxis (bleeding from the nostril) fitting both the animal and sire models were 0.23 and 0.40, respectively, which indicated that epistaxis as associated with EIPH in Southern African Thoroughbred sires has a strong genetic basis,” the study stated. “Genetic trends indicating an increase in epistaxis were also found.”
The results of the study were in line with what some trainers said during a panel discussion June 13. When asked whether Salix use was weakening the breed, California trainer Richard Mandella said he thought the relationship between families and breeding needed to be investigated.
“I believe I’ve had horses out of certain families and by certain sires, that I won’t name, that definitely tended to bleed more than others,” Mandella said. “I liken it to the hypertension issue. They are washy, nervous horses.”
The South African study went on to suggest that all stallion prospects that were treated with Salix while racing “should be barred from breeding and not be considered as future sires.” This is a policy currently followed by the German stud book.
“Estimated breeding values for epistaxis should be used as a tool for selecting against it and be considered in breeding programs to decrease the incidence thereof,” the study concluded.
McVeigh said the discussions held during the second-day of the medication summit need to keep the strong heritability of EIPH in mind.
“I think we all need to owe it to ourselves as to whether this is a red book condition,” he said. “We owe it to the horse.”