The aims of the present thesis were to evaluate the effect of melatonin treatment (MELOVINE subcutaneous implant 18 mg melatonin) in different aspects of livestock of Sarda sheep breed (considering season, lactating periods, male replacement during mating perdiod, puberty, different melatonin receptor genotype, milk yield and mammary immune system). This study was conducted in different farms located in Sardinia and similar for raising condition and animals managment, involving a great number of sheep. The data confirmed that melatonin is able to advance reproductive recovery in Sarda sheep breed in spring. Furthermore, the most suitable time to perform the melatonin treatment for the best response to the male effect is April-May. Melatonin treatment should be performed 3 or 4 months after lambing, in order to obtain optimal reproductive results. A weekly substitution of the males and their treatment with melatonin guarantees a better reproductive efficiency both in the adult ewes and in the ewe lambs. Another interesting conclusion is that treatment with melatonin in lactating sheep does not change the quantity and quality of milk and decreases the number of somatic cells, suggesting that this molecule can preserve health of the mammary gland. In conclusion, this thesis has provided many results directly applicable in Sarda sheep farms in order to improve reproductive efficiency, furthermore can give a new starting point to the development of research
