Melatonin implants do not alter estrogen feedback or advance puberty in gilts

Area of Science:

• Animal Reproduction
• Endocrinology
• Swine Production

Background:

• Puberty onset in gilts is influenced by seasonal factors, with long daylength suspected as a primary cause for delayed puberty in late summer and autumn.
• Estradiol's negative feedback mechanism plays a crucial role in regulating reproductive cycles, and its release timing is hypothesized to be season-dependent.

Purpose of the Study:

• To investigate if gilts born near the winter solstice experience a later release from estradiol negative feedback compared to those born near the spring equinox.
• To determine if melatonin treatment can advance puberty by altering estradiol negative feedback and accelerating puberty onset in gilts born near the spring equinox.

Main Methods:

• Determined optimal estradiol implant dosage for monitoring negative feedback release in ovariectomized gilts.
• Administered melatonin implants to assess effects on negative feedback in ovariectomized gilts and puberty onset in intact gilts across different birth cohorts (seasons).
• Monitored plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), and progesterone levels to evaluate reproductive status.

Main Results:

• Plasma LH and FSH levels increased with age (126-210 days) across all cohorts, but season or melatonin treatment showed no significant effect.
• Age at first detection of elevated plasma progesterone in untreated gilts decreased across the four birth cohorts.
• Melatonin treatment did not advance the age of puberty in intact gilts, irrespective of their birth season.

Conclusions:

• Estradiol sensitivity decreases with age in gilts, confirming established physiological principles.
• This study failed to demonstrate a significant effect of season of birth or melatonin treatment on estradiol feedback mechanisms or the advancement of puberty in gilts.