Opioid peptides and behavioral and physiological responses of dairy cows to social isolation in unfamiliar surroundings

To test whether endogenous opioid peptides are involved in the behavioral a nd physiological responses of cattle to stress, 12 Holstein cows were eithe r placed in social isolation in unfamiliar surroundings for 15 min or remai ned in their home stalls, either with or without naloxone treatment, follow ing a Latin square design. Vocalizations (judged as high or low frequency), defecation/urination, and heart rate were recorded, latency to respond to local thermal stimulation of the leg by means of a laser was measured to de tect pain sensitivity, and blood was sampled and assayed for cortisol conce ntrations. Naloxone in the home stall increased cortisol concentrations and tended to reduce response latencies to the laser but did not induce vocali zation. Social isolation increased the incidence of high-frequency vocaliza tion and of defecation/urination, heart rate, cortisol concentrations, and response latencies to the laser. Prior administration of naloxone increased the incidence of low-frequency vocalization in isolation, but it had no ef fect on heart rate or on responses to the laser and only limited effect on cortisol concentrations when the cows were isolated. Brief periods of socia l isolation in unfamiliar surroundings seem to be stressful to cows, as ind icated by increased heart rate, hypothalamic-pituitary-adrenocortical axis activity, and vocalization. Isolation also reduces pain sensitivity, sugges ting a stress-induced analgesia. However, we found no evidence that naloxon e-sensitive opioid receptors were involved in these responses.