The role of melatonin implantation and the associated effect of insulin-like growth factor- I on milk composition of Barki ewes

Context Manipulation of milk composition in lactating ewes represents an important mechanism by which sheep breeders can improve profits through increased milk prices for cheese making and higher lamb growth rates. To this end, melatonin implantation may affect milk composition by alleviating reproductive seasonality and augmenting insulin like growth factor-1 (IGF-I). This research aimed to evaluate the effects of melatonin administration on hormone levels and milk composition, and to determine its potential to manipulate milk composition of lactating Barki ewes. Methods. Fifty lactating Barki ewes were divided into two groups of 25. One group received 18 mg melatonin in a single implant at 40 days after delivery, and the other group served as an untreated control. Over the following 8 weeks, milk components (fat, protein, lactose and total solids percentages), milk energy value, and blood serum hormones including IGF-I were measured. Key results. Melatonin implantation increased (P < 0.05) IGF-I concentration, which showed continued elevation (P < 0.05) throughout the treatment period (from Day 14 to Day 56) relative to the control. Analysis of milk composition of implanted ewes revealed higher (P < 0.05) milk fat, protein, lactose and total solids percentages as well as milk energy value than in milk of control ewes. Conclusion. An integrated effect of melatonin and IGF-I successfully improved milk composition of lactating Barki ewes. Implications. Melatonin implantation can be used to improve milk composition of lactating Barki ewes, potentially increasing profits from cheese making and lamb production.