Melatonin administration as a strategy to mitigate weaning stress in Lacaune lambs

Weaning from artificial milk feeding represents a critical transition in intensively reared dairy lambs, involving dietary change, relocation, and social reorganization, all of which may compromise welfare, immune status, and growth performance. Melatonin, owing to its anxiolytic, antioxidant, and immuno-modulatory properties, has been proposed as a potential strategy to mitigate stress-related responses during this period.

Sixty Lacaune lambs were randomly assigned at weaning to one of three treatments: control (saline injection), intravenous melatonin (18 mg), or a slow-release subcutaneous melatonin implant. Behavioral patterns were recorded from Day -3 to Day 3 relative to weaning, and body weight was monitored until Day 31. Hematological parameters, serum cortisol, acute phase proteins (CRP and haptoglobin), and fecal Escherichia coli counts were assessed on Days -4 and 4.

Subcutaneous melatonin implants attenuated several behavioral indicators of weaning stress, including walking, bleating, and suckling attempts, and were associated with improved post-weaning growth performance from Day 11 onward. Intravenous administration produced limited effects. Cortisol concentrations increased in melatonin-treated lambs on Day 4, although this was not accompanied by adverse behavioral or productive outcomes. Most hematological parameters were unaffected by treatment; however, hemoglobin concentration increased selectively in the implant group. Acute phase proteins and fecal E. coli counts did not differ among treatments.

Sustained melatonin administration via subcutaneous implants improved behavioral adaptation and post-weaning growth without evidence of detrimental health effects. These findings suggest that slow-release melatonin may represent a promising supportive strategy during the weaning transition in intensive dairy sheep systems.