Effects of melatonin implants in ewe lambs.

Area of Science:

• Reproductive Endocrinology
• Animal Science
• Chronobiology

Background:

• The pineal gland produces melatonin, a hormone regulating circadian rhythms.
• Melatonin's role in reproductive seasonality and puberty onset in sheep is not fully understood.
• Constant light exposure can disrupt natural photoperiodic signaling.

Purpose of the Study:

• To investigate the effect of melatonin administration on the onset of puberty in female sheep (ewes).
• To determine if pinealectomy and exogenous melatonin influence prolactin levels and growth in ewes and their lambs.
• To elucidate the involvement of the pineal gland and melatonin in the control of reproductive maturation in sheep.

Main Methods:

• Pinealectomy was performed on ewes, followed by exposure to constant light.
• Lambs born to pinealectomized or unoperated ewes received subcutaneous implants of melatonin or empty controls.
• Puberty onset was monitored via weekly progesterone analysis, and prolactin levels and growth were assessed.

Main Results:

• Melatonin treatment significantly delayed the onset of puberty in ewe lambs (P < 0.05).
• Mean pubertal age was 44 weeks in control lambs versus over 72 weeks in some melatonin-treated lambs.
• Autumn prolactin levels decreased in control lambs but not in melatonin-treated lambs, correlating with ovarian activity.

Conclusions:

• Pineal gland function and melatonin are critical in regulating puberty onset in sheep.
• Exogenous melatonin can suppress reproductive maturation, indicating a direct role in controlling pubertal timing.
• Melatonin may influence seasonal prolactin changes associated with reproductive cycles in sheep.