Abstract
Crib biting is a common equine stereotypic behavior that has links to health problems and poor welfare. There is evidence that crib biters may be more sensitive to environmental stressors, and the aim of the present study was to test the hypothesis that crib-biting behavior in horses has a relationship with oxidative stress, antioxidant defense, or inflammatory proteins, as is observed in humans with various affective disorders such as depression and anxiety. Ten crib-biting horses and 10 age- and sex-matched healthy horses were used. Vital signs (heart rates, respiratory rates, and temperature) and blood samples were taken in 3 conditions; basal condition for crib biters (no stereotypic behavior observed for at least 30 minutes); crib biters during or directly after crib-biting periods (“acute crib biting” = crib biting for at least 15 minutes with no interruption longer than 2 minutes); non–crib-biting horses (control). Comparisons were made between crib biters and controls, and between crib-biters' basal and crib-biting values. No changes were observed in the vital signs. Total antioxidant capacity activity was significantly decreased in crib biters during the basal measurements relative to controls, and this was significantly decreased again during an episode of crib biting. Similar differences to those observed in total antioxidant capacity were also observed for the antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase. Collectively, our data suggest that the antioxidant levels and antioxidant defenses against lipid peroxidation are reduced in crib biters, suggesting that oxidative stress plays a role in the pathophysiology of crib biting. In addition, our data suggest that further study on the role of oxidative stress in crib biting might be of benefit, particularly in the search for veterinary treatments or interventions for crib-biting horses.