Forelimb Conformation and the Thoroughbred Racehorse

"What is the relationship between conformation and performance, and what can we do to impact it?" These questions have been asked by those focused on performance in many species, and they were the focus of one presentation by Liz Santschi, DVM, Dipl. ACVS, clinical associate professor at the University of Wisconsin-Madison, at the Western Veterinary Conference held Feb. 20-25 in Las Vegas, Nev.

After discussing the history of the Thoroughbred racehorse and the impact of breeding selection on its conformation, she discussed a study she recently completed, but has not yet published, on Thoroughbred racehorse conformation. To quantify just how common conformational problems were in the middle-of-the-road Thoroughbred population, she evaluated conformation, height, weight, sale price, and racing performance of nearly 300 horses in a 2-year-old sale. Knee and front fetlock conformation were most closely scrutinized for this study.

She reported that about half of the racehorses evaluated in her study exhibited multiple conformation defects, and that this was quite common in broodmares as well. In racehorses, "Carpal conformation was graded as straight (25%), only valgus (lower limb deviated outward from the knee or knock-kneed, 5%), only offset (lower limb set out from the upper limb, 27%), only outwardly rotated (22%), or possessing multiple deviations (22%)," she reported. "Fetlock conformation was summarized as straight (52%), inward deviation of either fetlock (10%), outward deviation of either (34%), or one in and one out (2%)." Only about a quarter of the horses evaluated had straight knees, and only about half had straight fetlocks.

Some conformational problems were strongly associated. "Carpal and fetlock conformation were strongly associated; 2-year-olds with multiple carpal deviations more commonly exhibited outward fetlock deviation and horses with offset carpal conformation exhibited inward fetlock conformation," she said.

Santschi found an association between carpal conformation and the number of starts in the 2-year-old year (horses that were valgus and outwardly rotated in their carpus (knee) made more starts). At two to four years of age, toed-in fetlock conformation was associated with likelihood of winning, and with likelihood of winning a greater percentage of races.

She also looked at workout speed during the sales and found that a faster workout was associated with more 2-year-old starts and a higher price paid for the horse. There were trends (not statistically significant) of association of a higher workout speed with a greater win percentage and earnings per start. There was a significant association between higher sale price and a horse’s ability to start and to win.

"The more you pay for a horse, the more likely he is to win for you!" she said with a laugh.

“These results vary somewhat from a recent study from Colorado State University that stated that valgus protects horses from injury,” she stated. “We believe the discrepancy is because our subjective evaluation allowed us to consider multiple deviations, rather than only valgus measurements from a photo. It is possible that valgus only conformation is not desirable, but that valgus along with other deviations may be helpful."

In conclusion, she said that a 2-year-old sale is a good place to buy a racehorse, straight forelimb conformation is overrated, and valgus (knock-kneed) conformation by itself is not desirable. "Deviation from straight conformation in the forelimb is common in 2-year-old Thoroughbreds sold as racing prospects, and not all deviations have a similar impact on limb motion and early athletic performance," she stated.

So What Does It Mean?

“The problem with conformation and performance is that conformational evaluation is subjective, and the rules are largely based on anecdotes. Of course there are horses that break those rules,” she said. “This makes it tough to get a handle on this problem. 'Assault had a bad club foot and won the Triple Crown,' etc. There are very few straight horses where you can't find any fault in their conformation at all, and lots of crooked horses that run quite fast.

"Evaluating a yearling and predicting future performance is like looking into a middle school yard and picking the track star," she went on. "You are going to pick some slow runners, and you are going to miss a few fast ones. Conformation evaluation is about narrowing the possible pool.”

Another problem is conformational variability, Santschi added. She cited an Equine Veterinary Journal study that evaluated top-performing 2- and 3-year old Thoroughbreds and 19 top stallions, and found that more than 65% of their conformational traits exhibited large phenotypic variation (greater than 10%) among this elite group of performers.

"So is it rational to develop an ideal, and criticize horses that don't match it?" she asked the audience.

Santschi commented that in the future she plans to conduct a study evaluating any relationship between conformation and catastrophic injury. "I'd like to focus on durability and preventing these injuries," she stated.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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