The aim of the study was to determine the effect of photoperiod and exogenous melatonin on milk yield and chemical composition of sheep's milk. Sheep (n = 60) were randomly divided into three groups: lambing in February (Group 1-n = 20), lambing in June (Group 2-n = 20), and lambing in June and treated with subcutaneous melatonin implants (Group 3-n = 20). Milk yield was higher for Group 1 and Group 2 than for Group 3 (p < 0.01). The milk of ewes of Groups 2 and 3 had a significantly (p < 0.01) higher content of dry matter, protein, and fat. Group 3 sheep's milk contained significantly more (p < 0.01) of SFA (Saturated Fatty Acids). The highest content of MUFA (Monounsaturated Fatty Acids) and PUFA (Polyunsaturated Fatty Acids) was found in the samples collected from Group 1, the lowest was in the milk of Group 3 animals. The highest (p < 0.01) CLA, content was identified in the milk of Group 1, while the lowest was recorded for the milk obtained from sheep treated with exogenous melatonin (Group 3). The experiment carried out has shown that day length and treatment with exogenous melatonin modulate the chemical composition of milk.
Keywords: melatonin; milk; photoperiod.