With the North American yearling sale season weeks away from launching July 11 at the Fasig-Tipton July Sale in Lexington, the role of veterinary evaluations in young sales horses moves to the forefront.
This year's discussions will be enhanced by the results of a study published June 23 in the Equine Veterinary Journal titled "Subchondral lucencies of the medial femoral condyle in yearling and 2-year-old Thoroughbred sales horses: Prevalence, progression and associations with racing performance," which was co-authored by Frances J. Peat, Christopher E. Kawcak, C. Wayne McIlwraith, David P. Keenan, Jeffrey T. Berk, and Daniel S. Mork.
Lucencies are areas of decreased bone density that can show up in varying degrees in a horse's stifle. Of particular interest is the medial femoral condyle, which is the rounded end of the femur that forms the stifle joint with the tibia. Abnormalities in this area are associated with lameness and may raise red flags about a horse's ability to hold up to training.
How the varying degrees of these lucencies are interpreted in sales prospects is controversial, however, because consignors see horses unfairly penalized by price for conditions that ultimately never affected their racetrack performance.
The results of this study take a step toward presenting a more accurate view of the risk that these findings actually pose regarding racing soundness based upon science.
"We wanted to test the idea that we may have been putting too much emphasis from a veterinary standpoint on some of the findings that may or may not affect these horses in terms of their racing soundness," said Berk, who has also been involved in research related to sesamoiditis in sales horses. "You can see that we may have been overestimating the level of risk presented by medial femoral condylar stifle findings in some of these horses."
The horses evaluated included 2,508 offered at the 2016 Keeneland September Yearling Sale and 436 juveniles offered at either the Ocala Breeders' Sales March, OBS Spring, OBS June, Fasig-Tipton Gulfstream, or Fasig-Tipton Midlantic May 2-Year-Olds in Training Sales.
Radiographs of the horses' stifles were graded from 0 to 3 by four veterinarians who went through a training period in advance to discuss the rating system and reach a consensus on how to apply the ratings to sample images. A majority of the images were read by two vets, one with 18 years of experience in evaluating sale repository radiographs and the other 10 years of experience.
The study found 85% of the yearlings evaluated eventually started in at least one race and 15% had not raced by the end of their 4-year-old year in 2019. The overall percentage of starters from foals for North American crops from 1997-2006 is 71%, and 81% for the foals representing the top 1% of North American sires by lifetime progeny earnings, according to The Jockey Club.
The probability of yearlings with a grade 3 lucency starting in a race was lower than yearlings with grades 0-2 (77.6% vs. 84.3-91.3%), but among the grade 3 horses that did start there was no statistical significance in racing performance.
The number of horses identified with a grade 3 lucency was relatively small at 26 (1%) out of the 2,508 horses evaluated. Among the 2-year-olds, only five were rated as grade 3s. The vast majority of the yearlings were grade 0 (90.4%) and among the 2-year-olds, 88.8% were grade 0.
The study included 422 horses that were evaluated at both yearling and 2-year-old sales. Of the 31 grade 1 yearlings in this group, 11 (35.5%) were later reassessed as grade 0 as juveniles, and 14 (45.2%) remained at grade 1. Six of the grade 1 yearlings (19.4%) developed grade 2 lucencies. Among 10 horses assessed as grade 2s as yearlings, six (60%) remained at grade 2 as juveniles, two (20%) improved to grade 1, and two progressed to grade 3.
Horses in this study included 389 that never raced. Among these non-starters, the researchers were able to get some follow-up information on 166 (43%) of the horses and complete information about 82 non-starters. Sixty-six non-starters did not race because of issues related to performance: 45 involved lameness, 14 had insufficient athletic talent, three had upper respiratory tract dysfunction, one did not start due to behavior issues, one due to severe muscular tying up, one was a wobbler due to cervical vertebrae malformation, and one had recurring exercise-induced pulmonary hemorrhage.
Of the 45 who did not start due to lameness, four involved a clinical diagnosis related to the stifle. With three of them, the specific structural issue was unknown, and one had gotten kicked in the stifle. None of the later evaluations of the four lameness cases mentioned MFC lucencies and all four were assessed at grade 0 on their yearling radiographs.
As for performance, the 2,119 horses that raced included 84% that did not start in a listed or grade/group rated race. These starters also included 4.8% that made their highest-rated start in a listed stakes, 4.2% made their highest start in a grade/group 3, 3.1% in a grade/group 2 race, and 4.3% in a grade/group 1 race.
The study did not find any significant association between the horses' lucency grades and their eventual career-best starts as racehorses. The median Class Performance Index, an earnings-based index that compares a horse's earnings with the average for all runners in a given year and in a specific country, was 1.47 for all studies' runners, whose CPIs ranged from 0-88. The study also did not find any significant association between lucency grades and CPI.
Conclusions do note that the number of horses with severe lesions may be undercounted because horses that developed a lameness were more than likely withdrawn from a sale and not included. The study also does not account for yearlings with grade 3 stifle findings that were treated surgically prior to racing, and the use of analgesics could not be accounted for.
"Based on science, this study goes a long way toward giving people a comfort level with a horse that maybe they should buy," Berk said. "There are other variables that we cannot measure that make for a quality racehorse. Those variables that we can measure need to present the accurate level of risk associated with racing outcomes based on studies like this.
"You definitely have options, even if you were to purchase a grade 3 stifle which became clinical," he added, noting there are several successful surgical options available.
"The average person reading this study will realize that not everything we find in the stifle in that location matters. ...In an ideal world there should be no difference between a horse that is OK to purchase for racing as opposed to pinhooking, if everyone understands the information. And I understand that is a big if."