Is There a Genetic Link Between Resting Infrared Thermography in Young Horses and Longevity in Jumping Competition?

The objective was to evaluate the genetic relationship between the surface temperature of regions of interest, measured using infrared images of young horses and functional longevity in jumping. This relationship was assessed by comparing the temperatures measured in the offspring of two groups of sires, one favourable and one unfavourable, to longevity. The study used a specific data collection protocol on a sample of 921 young progeny, before they began competing, of 141 extreme stallions, comprising 61 favourable and 80 unfavourable sires. These stallions had been selected based on estimated breeding values for functional longevity derived from official competition data of 202,320 horses. Infrared imaging provided 49 temperature variables, including average and maximum values for regions of interest such as temperature differences from the body for eyes, hocks, fetlocks, feet, carpi and back. It also included differentials between these regions, asymmetry between right and left sides and variability within each area. Heritability was estimated using a mixed model with fixed effects, of age, sex, coat colour, weight and visit, along with random genetic effects (considering a pedigree of 8002 horses). The effect of temperature on the group of sires was assessed using multivariate partial least squares logistic regression, adjusting temperature for fixed effects. Results indicated high heritability for the temperature of regions of interest: body (0.53 ± 0.14), carpi (0.55 ± 0.19), fetlocks (0.47 ± 0.12), feet (0.46 ± 0.12 and 0.38 ± 0.12). Lower heritability was observed for differences between regions (around 0.20) and even lower for asymmetry and variability. Lower average and maximum eye temperatures, lateral asymmetry in hind feet temperature and temperature variability in the back were associated with a higher probability of belonging to the favourable group of sires for functional longevity. Infrared imaging may be a tool for identifying easily measurable selection criteria associated with longevity. Given the limited number of horses, the limited number of significant variables associated with the group of sires and the specificity of the protocol, verification and validation studies are necessary before its use.