Potential role for selenium in the pathophysiology of crib-biting behavior in horses

Crib-biting is a repetitive and compulsive behavior that is characterized by “grasping a fixed object with incisor teeth and aspirating air with an audible grunt.” Little is known about etiology and pathophysiology of crib-biting behavior in horses. Previously, we have shown that oxidative stress is linked to crib-biting, with crib-biters showing lower antioxidant capacity than non-crib-biting horses. The aim of the present study was to extend our understanding of oxidative stress in crib-biting to determine the serum contents of some mineral trace elements (manganese [Mn], magnesium [Mg], selenium [Se], copper [Cu], and zinc [Zn]), and electrolytes (sodium [Na], potassium [K], calcium [Ca], and phosphorus [P]). Also, the activity of enzymes (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and gamma glutamyl transferase), some hormones (cortisol, ghrelin, β-endorphin, and serotonin) and blood biochemistry values of various parameters was measured to evaluate their possible association with crib-biting behavior in horses. Blood samples were taken from all horses under the following conditions: basal conditions of crib-biting horses, during or immediately after crib-biting periods, and from non-crib-biting, healthy horses (control group). Serum Se concentration was significantly lower (P ≤ 0.001) in crib-biting horses than in controls, with the lowest levels seen during crib-biting behavior. Other measured parameters did not differ between acute crib-biting horses and healthy controls. These observations suggest that alterations in serum Se, an important component of the antioxidant system, may play a role in the pathophysiology of crib-biting behavior in horses, adding further evidence to the theory that crib-biting may be related to increased oxidative stress and alterations in essential trace elements.