Melatonin rhythms in Pony mares and foals.

The research article involves a comprehensive study on the rhythm of melatonin secretion in Pony mares and foals, focusing on the influence of photoperiod (light and dark durations), surgical removal of superior cervical ganglia, and the age of foals.

Melatonin Concentrations in Mares

• Naturally, Pony mares display higher melatonin levels during night time than in the day. This study discovered that the same pattern couldn’t be observed in mares that had their superior cervical ganglia removed. It strongly suggests that the removal of superior cervical ganglia might interfere with the normal melatonin cycle.

Impact of Photoperiod Changes

• In a separate experiment with 4 Pony mares, the effects of a light-dark cycle (10 hours of light and 14 hours of darkness) were compared against continuous darkness. At the end of three weeks in each condition, melatonin levels were observed to be significantly higher under continuous darkness. This result indicates that light conditions significantly affect the melatonin secretion in mares.
• Despite continuous darkness, the melatonin levels still displayed rhythmic changes but the coordination with day/night rhythms or among other mares was absent. This lack of coordination suggests that mares’ internal biological clocks might get disoriented in a prolonged darkness scenario, thereby losing synchronization with ‘external’ day-night cycles.

Comparison of Melatonin Rhythms in Mares and Foals

• Finally, the research also studied the time evolution of melatonin rhythms in 3 mares and their corresponding foals, while they were exposed to natural lighting in open pens.
• While clear melatonin rhythms were observed in mares throughout the foal’s growth from 1 week to 11 weeks of age, the melatonin levels in foals only began showing significant time trends when they were 7-11 weeks old. This result suggests that the establishment of distinct melatonin rhythms might be linked with the maturity of the foals and their ability to adapt to external day-night cycles.