[Melatonin and reproduction in domestic animals]

Melatonin, synthetized by the pineal gland, is the chemical messenger which allows seasonal animals to perceive day length changes. In the ewe, the nervous message, transformed into a hormonal one, triggers pulsatile activity of the LHRH neurons. About 40 days are necessary for melatonin to centrally stimulate the pulsatile LHRH activity. Its sites and mode of action are not completely elucidated, but a precise hypothalamic zone has been defined in which radioactive melatonin binds specifically and where cold melatonin delivered locally stimulates LHRH activity. In veterinary clinic, the most frequent mode of distribution is the sub-cutaneous implant, which induces an advance of the cyclical ovulatory activity of ewes and goats. The date of fertilization is advanced and fecundity of females is improved. It can be used alone, or in association with other hormonal treatments, or after an artificial photoperiodic treatment. Under these conditions, it allows a quantitative and qualitative increase in out-of-season sperm production in rams and he-goats. Such an implant is registered and marketed in France, UK, Greece, Australia and New-Zealand.