Oxidative Stress and Blood Parameters During Shearing in Sheep Treated with Melatonin

Shearing is a stressful procedure for sheep, combining isolation, restraint, and the mechanical action of shearing, which activates the hypothalamic-pituitary-adrenal axis and induces oxidative stress. This study investigated whether melatonin-a pleiotropic hormone with well-documented antioxidant properties-administration could modulate the stress response and oxidative stress in Sarda sheep during shearing. Forty lactating ewes (aged 3-5 years, mean body weight 41 ± 1.1 kg) were randomly assigned to four groups (n = 10 each): two groups received a subcutaneous melatonin implant (18 mg); two remained untreated as controls. Within each category, one group was shorn and the other subjected only to restraint. Blood samples were collected before, during, and after shearing to measure cortisol, glucose, reactive oxygen metabolites (ROMs), biological antioxidant potential (BAP), and oxidative stress index (OSI). Procedures elevated cortisol, glucose, ROMs, and OSI in all groups, but melatonin treatment significantly reduced these parameters and increased BAP relative to untreated animals at all sampling points (p < 0.05). No significant differences were observed between shorn and unshorn animals within the same treatment, suggesting that the handling, restraint, and isolation associated with the shearing procedure represent the major sources of stress, rather than the mechanical act of shearing itself. In conclusion, melatonin administration blunts the stress response and reduces oxidative stress in sheep during routine shearing-related handling procedures, suggesting its potential as a practical tool to improve animal welfare during routine management practices.