Impact of Photoperiod Length and Treatment with Exogenous Melatonin during Pregnancy on Chemical Composition of Sheep’s Milk

SIMPLE SUMMARY: The high content of valuable nutrients and biologically active substances in sheep’s milk positively affects the dietary value of this milk and products derived from it. Studies carried out so far indicate that for ewes, the date (season) of lambing, and thus also the period when lactation is initiated influences the biochemical parameters of milk. Results from the experiment carried out by the authors can serve as foundation for usage of sheep’s milk in so-called nutritional programming in the treatment of many human diseases. In seasonal animals such as sheep, length of day and melatonin signal have a significant impact on lactation parameters and chemical composition of milk. Sheep’s milk offers a number of health-promoting properties and can be used in prevention of many human diseases. An important factor contributing to these beneficial properties of sheep’s milk is its fat content, which is rich in bioactive substances, such as CLA (Conjugated Linoleic Acid), with antioxidant properties. ABSTRACT: 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.