Melatonin can induce early onset of the breeding season in ewes

Abstract

Patterns of plasma melatonin, similar in the duration of high levels to those found in winter, were induced in Suffolk-cross ewes kept in summer light (16 h light: 8 h darkness) by daily oral administration of melatonin (3 mg/13 mumol). The onset of oestrous cycles in these sheep occurred in August, 2-8 weeks before the onset of oestrous cycles in untreated ewes kept in natural light. The onset of oestrous cycles in a further group of ewes kept in winter light (8 h light: 16 h darkness) from mid-June was indistinguishable from that of the melatonin-treated ewes. Rams were excluded from the premises. These data indicate that melatonin alone in physiological quantities is sufficient to induce early onset of the breeding season in the ewe, and provide strong evidence for a hormonal role of melatonin in a short-day breeder.

The use of light and melatonin treatments in the preparation of Suffolk rams for out-of-season breeding

“…It has been established that melatonin is produced by the pineal gland only during the period of darkness and that it plays a key role in the periodicity of Soay rams (Almedia and Lincoln, 1984) and of Suffolk ewes (Arendt, Symons, Land and Pryde, 1983). Recent investigations have shown that melatonin treatment may replace the 'long night' phase of light treatments, and that a high level of fertility may be achieved in adult Suffolk ewes (Williams, 1984(Williams, ,1985Williams and Ward, 1988).…”

Testicular function and semen characteristics of Awassi rams treated with melatonin out of the breeding season

“…Melatonin can be used alone, or combined with other hormonal treatments, after an artificial light (photoperiodic) treatment. In several studies concerning ewes of different breeds, melatonin administration has been found to advance the onset of reproductive activity (Arendt et al, 1983;Karsch et al, 1984;English et al, 1986); furthermore, melatonintreated ewes appeared to have better oocyte quality and higher ovulation and conception rates (Stellflug et al, 1988;Kouimtzis et al, 1989;Tsiligianni et al, 2009).…”

Short- and long-term effects of manipulation of the pineal/melatonin axis in ewes

“…Independent confirmation of the ability of melatonin treatments to advance the breeding season and decrease prolactin followed (Nett and Niswender, 1982 ;Arendt et al, 1983 ; Symons, Arendt and Laud, 1983 (Kennaway and Gilmore, 1984 ;Kennaway et al, 1986). Pinealectomy at 10 weeks of age similarly results in puberty delay (Kennaway, Gilmore and Dunstan, 1985).…”