Veterinary pre-purchase examination results as an indicator of subsequent athletic performance in national hunt thoroughbred horses

Conformational and other defects can affect the soundness of a horse and impede athletic performance to varying degrees. This study sought to investigate the prevalence of a variety of anatomical defects, to determine heritability estimates for a selection of these defects and to investigate the effect of a variety of these defects on the racing performance in a large sample of young Thoroughbred horses presented for sale. The study population consisted of data from 13,603 pre-purchase veterinary examination certificates for three and four year old Thoroughbred National Hunt (NH) horses. The information was gathered using the Pre-Purchase Veterinary Examination Certificates from eight years of Tattersalls Ireland’s Derby Sale, Goffs Ireland June Sale and Doncaster Bloodstock Sales Ltd. (DBS) Spring Sale (2002-2009) and seven years of Tattersalls Ireland’s August Sale (2002-2008). All conditions noted by the veterinarian were recorded in order to determine the true prevalence of defects in this National Hunt population. It was found that 73.58% of the sample population had one or more defects with 12.02% having serious defects likely to prejudice their use for racing. Metacarpal/metatarsal exostoses and tarsal plantar desmitis affected 17.11% and 19.40% of the sample, respectively, while 9.81% of the horses were found to make respiratory noises and 5.26% had recurrent laryngeal neuropathy (RLN). Age, sex and year of birth had a significant effect on the occurrence of many of the defects and panel veterinarians were significantly more likely to diagnose defects than the private veterinarians (p < 0.001). To estimate h2 values a pedigree file, three generations deep was generated and heritability (h2) estimates were estimated using an animal model. The h2 values ranged from 0.01 (±0.008) for calcaneal bursitis to 0.52 (±0.044) for price. Heritability estimates for the defects were highest for tarsal plantar desmitis (0.23 [±0.030]), respiratory noise (0.13 [±0.021]), RLN (0.10 [±0.019]) and metacarpal/metatarsal exostoses (0.10 [±0.020]). The h2 values were below 0.10 for the remaining defects. Phenotypic correlations were found to range from 0.00 (±0.011) for pelvic asymmetry and being unsold, to 0.65 (±0.006) for respiratory noise and being withdrawn from the sale. The strongest genetic correlation observed was also between respiratory noise and being withdrawn from the sale with a value of 0.99 (±0.298). The strongest genotypic correlations between defects were found between RLN and respiratory noise (0.91 [±0.035]), RLN and prejudicial defects (0.96 [±0.023]) and respiratory noise and prejudicial defects (0.90 [±0.039]). There were also very strong positive genetic correlations between being withdrawn from the sale and the presence of prejudicial defects (0.96 [±0.173]), respiratory noise (0.92 [±0.196]), and RLN (0.99 [±0.298]). Only horses entered into the sales from 2002-2004 were examined to determine the effect of the anatomical defects on racing performance. At least four years of possible racing results were available for each horse. Sex, selling status and price realised at sale had a large effect on the racing performance of the horses in the sample. Mares had significantly fewer career starts (8.07+0.223 compared to 10.36+0.146), wins (0.49+0.033 compared to 1.03+0.030) and places (1.19+0.060 compared to 1.90+0.045) than geldings (P < 0.001). Horses that were sold had significantly more career starts, wins and places (10.04+0.143, 0.96+0.029 and 1.81+0.044, respectively) than horses that were not sold (9.14+0.290, 0.71+0.052 and 1.51+0.083, respectively) or that were withdrawn (8.88+0.452, 0.71+0.089 and 1.41+0.125, respectively) from the sale (P < 0.05) and horses that were in the higher price brackets at the sales had significantly more career starts (10.86+0.234 for horses >€20,001 compared to 8.19+0.276 for horses <€5,000), wins (1.31+0.053 for horses >€20,001 compared to 0.47+0.037 for horses <€5,000) and places (2.15+0.077 for horses >€20,001 compared to 1.14+0.075 for horses <€5,000) than horses in the lower price brackets (P < 0.001). Horses with prejudicial defects were significantly less likely to race (70.4% raced compared to 83.7%) or to win a race (33.8% compared to 41.3%) and had significantly fewer career starts (8.68+0.379 compared to 9.91+0.131), wins (0.69+0.071 compared to 0.92+0.026) and places (1.39+0.115 compared to 1.76+0.040) than horses without prejudicial defects (P < 0.01). Horses with RLN were significantly less likely to race (69.4% compared to 83.6%) than those without RLN and had significantly fewer career wins (0.68+0.092 compared to 0.92+0.026) and career places (1.35+0.155 compared to 1.76+0.040) than those without RLN. They also had a significantly higher proportion of non-finished races than those without RLN (34.01%+2.147 compared to 25.29%+0.456). Horses with tarsal plantar desmitis also had a significantly higher proportion of non-finished races than those without tarsal plantar desmitis (29.96%+1.754 compared to 25.71%+0.489). Papillomas significantly adversely affected the number of career starts (8.45+0.470 compared to 9.87+0.128), career wins (0.59+0.079 compared to 0.91+0.025), career places (1.30+0.126 compared to 1.75+0.039) and mean earnings per start (£241.5+41.85 compared to £454.6+21.93). Horses with papillomas had significantly more non-finished races than those without papillomas (33.34%+2.124 compared to 25.85%+0.448) while interestingly, horses with sarcoids had significantly fewer non-finished races than those without sarcoids (19.44%+1.805 compared to 26.58%+0.452). Overall, the results indicate that a large proportion of Thoroughbred National Hunt horses are affected by defects of some kind. The results show that the prevalence of a large number of defects increases with age and that certain defects are viewed negatively by purchasers, thereby affecting the selling status. There was a heritable component to each of the defects and each defect was found to affect racing performance to some degree. The results indicate that veterinary pre-purchase examinations make a significant contribution in the evaluation of potential racehorses and that buyers’ estimates of value appear to correspond with subsequent racing performance. It may be of benefit to the Thoroughbred industry to monitor the prevalence of defects within the population. The low heritability of the more serious defects does suggest that genetic progress in the reduction of these defects in the horse population would be slow.