The Forelimb Conformation of Thoroughbred Racing Prospects and Racing Performance from 2 to 4 Years of Age

Conformational deviations are common in young Thoroughbred racing prospects. Straight conformation of either the carpus or fetlock is not associated with improvements in the performance factors measured. Valgus-only and out-only carpal conformations had a negative effect on the 2-yr-old race record but not on the 2- to 4-yr-old record. Faster workout times for racing prospects at auction were associated with improved accomplishment in some measures of racing performance.

1. Introduction

Veterinarians are often asked to evaluate forelimb conformation in young racing stock. In young foals, the concern is the management of limb deviations [1], and in older horses, the prediction of performance and injury is of concern [2]. There is some information available about conformation and injury [2,3] but no data evaluating performance. The goal of this study is to evaluate 2-yr-old (2YO) racing prospects with an emphasis on forelimb conformation and to determine associations with racing performance from 2 to 4 yr of age.

2. Materials and Methods

In April of 2002, 292 2YO Thoroughbred racing prospects (subjects) were evaluated by inspection at rest and during a short walk in hand. Conformation was graded by the consensus of two observers. Additional data recorded included age, gender, speed of their fastest workout, and last bid price (sold or not). Race records were obtained from the Jockey Club at the conclusion of 2004. Analyses were performed using SAS software [a]. Determination of relationships between continuous and categorical factors or between two continuous factors was made using analysis of variance (ANOVA) or regression, respectively, proc mixed. When both factors of interest were categorical, the determination was made using either a χ2 test or Fisher's exact test in PROC FREQ. Significance was set at p < 0. 05.

3. Results

The average age of subjects was 26 mo (range = 22 - 28 mo), and there were 154 fillies and 138 colts. Carpal deviations considered were valgus, outward rotation, and offset. For analysis, subjects were assigned a summary carpal grade that described both forelimbs. Unilateral mild deviations were not considered when assigning a summary grade. Carpal conformation grades were straight (23% of subjects), valgus (5%), outward rotation (22%), offset (26%), valout (valgus and outwardly rotated, 6%), valoff (valgus and offset, 3%), outoff (outwardly rotated and offset, 13%) and triple combination (TC; valgus, outward rotation, and offset, 1%).

Fetlock conformation was graded as straight (53%), outward deviation (34%), or inward deviation (13%). The average increase in time over the fastest work of the day (BDA) to run .2 mi was 0.66 s (range = 0 - 2 s).

The racing performance of subjects at 2YO was 193 (66%) started a race and made an average of 4.7 starts. Races were won as 2YO by 92 subjects (49% of starters). The racing performance of subjects from 2 to 4 yr of age was 266 (91%) started a race, 266 made an average of 17.4 starts (1 - 61 races), and 216 (81% of starters) won a race. The median amount won at 2 - 4 yr of age for all subjects was $23,079 (range = $0 - 803,000), and the median earnings per start were $1557.

There were 11 significant associations (p < 0. 05) between subject factors (age, gender, carpal and fetlock conformation, and workout speed) and racing performance. Older horses at sale time were more likely to win as 2YO (winners mean age = 25.9 mo, 2YO with no wins mean age = 25.5 mo) and made more starts at 2 - 4 yr of age (each 1 mo of age increase resulted in .02 more starts). Fillies won a greater percentage of races (15.1%) than colts (11.3%). Faster sale workouts were associated with winning a race as a 2 - 4-yr-old horse (winners BDA = .63 s, non-winning horses BDA = .76 s), a greater win percentage at 2YO (each 0.1 s increase in BDA decreased winning percentage by 1. %) and at 2 - 4 yr of age (each 0. 1 s increase in BDA decreased winning percentage by 1.1%), and greater total earnings (each 0.1 s increase in BDA decreased total earnings by $3934) and earnings per start (each 0.1 s increase in BDA decreased total earnings per start by $277). Carpal conformation was associated only with 2YO racing performance. The odds of starting as a 2YO were 2.7 times greater for horses that were not only carpal valgus. Valgus-only and outwardly rotated-only horses made less 2YO starts (valgus mean = 1.6; outward rotation mean = 2.4) than their combination (valout mean = 5.2). Fetlock conformation was associated only with an ability to win from 2 to 4 yr of age. Horses with inward fetlock deviations won 17.7% of races; horses with outward deviations won 13. 7% of races, and horses with straight forelimb conformation won 12%.

4. Discussion

We were not able to detect any improvement with age in racing performance for horses with straight forelimb conformation, suggesting that the importance of straight forelimb conformation is overemphasized. Carpal conformation could be associated only with the 2YO race record and was not an indication of later ability. The improved racing performance associated with faster sale workout times suggests that BDA may be a useful indicator of racing ability.

This study was funded by the Equine Research Fund of the University of Wisconsin-Madison.

Footnotes

1. SAS Software, SAS Institute, Inc. , Cary, NC 27513.