Effects of pinealectomy in Pony mares.

This research examines the effects of the removal of the pineal gland (pinealectomy) in pony mares, finding it disrupts their response to photostimulation, which is related to reproductive patterns.

Key Findings

• The study shows that mares that have had their pineal gland removed at any point of the year show no significant difference in their annual ovulation date during the first year after the procedure. However, in the second year, those winter pinealectomized mares exhibit a significant delay in ovulation, indicating a long-term effect of pineal involvement in seasonal reproductive patterns.
• When pinealectomized mares were exposed to light that would normally stimulate ovulation, there was no advancement in the average date of the first year’s ovulation. This result was similar to that of mares where the pineal gland was intact but received no stimulatory lighting. Consequently, this suggests that the lack of a pineal gland blocks the ability of mares to respond to photostimulation.
• In mares with an intact pineal gland, plasma melatonin concentrations significantly increased during periods of darkness. However, in pinealectomized mares, there were no significant trends related to time.

Implications

• The pineal gland, responsible for releasing the hormone melatonin, seems to play an essential role in ovulation and reproduction patterning in pony mares. When removed, it disrupts their response to photostimulation, a standard method for manipulating the breeding season in horses.
• The research findings provide valuable insights into equine physiology, possibly influencing livestock management and veterinary practices. It underscores the potential longer-term effects of disrupting the function of the pineal gland.
• The non-responsiveness to photostimulation implies that the light signals normally received and processed by the pineal gland, causing changes in melatonin levels, are crucial for appropriate reproductive behaviour in horse mares.