Polymorphisms of the Dopamine D4 Receptor Gene in Stabled Horses are Related to Differences in Behavioral Response to Frustration

In stabled horses, behavioral responses to frustration are often observed, especially around feeding time. These behavioral responses are a useful indicator of their welfare. In this study, we investigated the association between this behavioral indicator and DRD4 gene polymorphisms in stabled horses. Twenty one horses housed in two stables were used. The horses were observed for approximately 4 h around feeding over three or more days using focal-sampling and instantaneous-sampling. Horses were genotyped for the A-G substitution in the DRD4 gene. The effects of the A-G substitution (with or without the A allele in the DRD4 gene), the stables, and their interaction on the frequency of behavioral responses to frustration were analyzed using general linear models. The total time budget of behavioral responses to frustration was higher in horses without the A allele than in those with the A allele (P = 0.007). These results indicate that the A-G substitution of the DRD4 gene is related to frustration-related behavioral responses in stabled horses. Appropriate consideration should be made for the DRD4 gene polymorphism when the welfare of stabled horses is assessed, based on this behavioral indicator.