The impact of barefoot racing in young Swedish trotters on career length.

In several European countries, racing without shoes, ie barefoot, is a common strategy in trotting races to improve the speed of the horse. Why some trotters can race barefoot without damage to the hoof from excessive wear and others cannot has been shown to partly be explained by differences in hoof composition. In particular, durable hind hooves are believed to be important to sustain racing without shoes. Also, variation in the proportion of the races the horse races with barefoot hind hooves has been shown to be affected by genetic differences in Swedish Standardbred trotters (SB) and Swedish-Norwegian Coldblooded trotters (CB). When racing barefoot, the protective properties of the shoe, which prevent the hoof from excessive wear and tear, are absent. If the hoof cannot withstand wear and tear, the damage of the hoof may pose a risk to animal welfare. The question of how barefoot racing should be regulated, especially for young horses, is under discussion in Sweden and elsewhere in Europe. Regulations regarding barefoot racing in young horses differ between countries, and there is a lack of published studies to base regulations on. Therefore, this study aimed to analyze the effect of racing with barefoot hind hooves in young SB and CB on career length. Datasets including shoeing information from 3-year-old SB, and 3- and 4-year-old CB were analyzed, including up to 12,161 horses. Cox proportional hazard models were fitted to analyze the effect of proportion of barefoot races at a young age on the hazard of ending the career at a given time point. Other effects such as sex, year of birth, started as a 2-year-old or not (SB only), early earnings, best racing time, and number of early starts were also included in the models. For SB, horses that raced more than 30% barefoot had a 14% higher hazard of ending their career at a given time point compared to the reference group that raced 5% or less barefoot. In CB, the hazard of ending the career at a given time point was 67% higher in the group with the highest proportion of barefoot races compared with the reference group. Although for SB, the reduction of the career length in days was minor. For CB, the effect was larger and verified the negative effect in SB but estimated based on fewer observations. Further studies of voluntary as well as involuntary reasons why Swedish trotters end their careers are needed to better understand the possible impact of racing barefoot as a young horse.