Effect of exogenous melatonin on the ovary, the embryo and the establishment of pregnancy in sheep

Abstract

Administration of melatonin to advance the breeding season in sheep has been widely used, since this hormone conveys the photoperiodic signal to the reproductive neuroendocrine axis. An increased lambing percentage has been reported following such treatment during anoestrus, which could be mediated through a higher rate of embryonic survival, either by an improvement in luteal function or by a reduction in the antiluteolytic mechanisms. The aim of this article is to review the body of knowledge on the effect of melatonin on the ovine ovary, the embryo and the establishment of pregnancy. Some studies using synchronized ewes have found that melatonin treatments during anoestrus do not improve ovulation rate by modifying the timing of follicle emergence, but increasing the number of ovulatory follicles by decreasing the atresia of medium and large follicles. On the other hand, the addition of melatonin to the in vitro maturation medium does not improve oocyte maturation rate in oocytes from sheep ovaries recovered either in anoestrus or in the breeding season. However, a luteotrophic effect of melatonin at either short or medium term has been reported. We have recently observed that melatonin implants tend to improve the survival of embryos collected from ewes after superovulation in anoestrus. More specifically, melatonin induced a significant reduction of the number and rate of non-viable (degenerate and retarded) embryos. Preliminary data from our laboratory suggest that the uterine sensitivity to progesterone -in terms of progesterone receptor expression -of superovulated ewes could be reduced by melatonin treatment. It can be concluded that the success of exogenous melatonin as a means to improve lamb production of sheep is due, at least in part, to an improvement of luteal support and embryonic survival.

Effect of exogenous melatonin on embryo viability and uterine environment in undernourished ewes

“…Stenbak et al (2001) reported that the fertilization rates of oocytes recovered from superovulated ewes were higher in the reproductive season than they were in anestrus. A previous study of our group demonstrated that treatment with exogenous melatonin at lambing improves the viability of ovine embryos from undernourished ewes during the anoestrous period, although the effects of exogenous melatonin on the ovary and early embryos remain unclear (Abecia et al, 2008;Vázquez et al, 2010b).…”

The effects of melatonin on in vitro oocyte competence and embryo development in sheep

“…Those effects are associated with an improvement in ovulation rate , luteal function (Durotoye et al, 1997;Abecia et al, 2002) and embryo viability (Forcada et al, 2006). For a summary of the effects of exogenous melatonin on the ovary and early embryos in ewes, see Abecia et al (2008). The high amphilicity of melatonin promotes its rapid transfer into organs and fluids, and this pineal hormone can rapidly pass through cellular membranes.…”

Supplementation of Slow‐Release Melatonin Improves Recovery of Ovarian Cyclicity and Conception in Summer Anoestrous Buffaloes (Bubalus bubalis)

“…Role of melatonin in the regulation of the circadian and annual rhythm has been exploited to modulate ovarian activities in seasonal species such as sheep (Abecia et al. ), goat (Kumar and Purohit ) and mare (McManus and Fitzgerald ); this investigation points to similar role of this hormone in buffalo reproduction.…”