Use of melatonin implants and photoperiodic treatments to control seasonal reproduction in sheep and goats

Abstract

Melatonin is a natural compound naturally secreted by the pineal gland during the dark phase of the light/dark cycle, which transduces the photoperiodic information in mammals. The continuous administration of melatonin via a subcutaneous implant, as described here, allows to mimic short days while animal’s eyes perceive long days of spring and summer. It is necessary to impose an alternation between long and short days in order to control the period of sexual activity.

In ewes under natural mating, a subcutaneous implant of melatonin (Melovine®) is inserted from 30 to 40 days before joining. The various experiments realised since some years in 5 French sheep breeds, and which compared in the same flocks treated and control ewes, have shown that fecundity of treated ewes is much higher than that of control ewes (16 lambs more per 100 ewes joined). Dates of lambing are more precocious and less spread in treated than in control ewes. Always in the ewe, in association with "classical" hormonal treatments for the control of oestrus and artificial insemination, melatonin treatment allows to significantly increase fecundity for the total induced oestrus and returns (30 lambs born more compared to control ewes).

In the dairy goat, due to the strong demand existing for an out-of-season breeding (from April to July), it is recommended to impose a photoperiodic treatment (extra light with a fixed dawn and a nocturnal lighting) during more than 2 months before implant insertion. Natural mating is done by introducing treated bucks among the female goats, from 35 to 70 days after the end of the photoperiodic treatment, in order to use the "buck effect". Under these conditions, fertility is close to that normally observed during the annual breeding season (higher than 80 %) and fertilisations occur about 10 days after introduction of bucks. Litter size is close to that of the normal breeding season. The association with "classical" hormonal treatments and AI is on test.

In the ram, insertion of melatonin implants allows an advance of testicular growth and an improvement of sperm production. If a full out-of-season sperm production is wished, as in AI centres, it is necessary previously to the insertion of implants to impose a light treatment composed of real long days or long days mimicked by one hour of extra light during the photosensitive phase. Such a treatment stimulates testicular growth, improves sexual behaviour, sperm production and increases fertility after AI, when compared to control rams. It is also possible to impose an alternation of one month of long days and one month of short days, which induces the maintenance of an elevated and constantly high sperm production during consecutive years. In open barns, in males left under natural lighting, the alternation of one month of extra light during the night with one month of melatonin treatment allows to reach the same results, removal of implants at the end of treatment remaining, however, difficult.

In the buck, the same type of rapid alternation between long days and short days allows to maintain high sperm production of good quality during more than 3 consecutive years. Under such conditions, the number of deep-frozen sperm doses is much higher than that of control bucks (from 41 to 69 % more). Fertility of artificially inseminated goats is not different from that of goats inseminated with semen of control bucks.

Melatonin implants Melovine® had obtained in 1995, the official registration in France.