Can the reduced GH, IGF-1, and ovarian steroids concentrations be considered as suspected biomarkers of age-associated functional deficit in mares?

Overview

• This study investigated whether declining levels of growth hormone (GH), insulin-like growth factor 1 (IGF-1), and ovarian steroids in mares are linked to age-related functional decline.
• The research measured GH, IGF-1, estradiol-17β (E), and progesterone (P) in mares of various ages to determine their relationships and changes with aging.

Introduction and Background

• In humans and experimental animals, the somatotropic axis (including GH and IGF-1) declines with age, affecting bodily functions.
• While IGF-1’s decline with age is documented in horses, the effects on GH and their interrelationships remain unclear.
• GH and IGF-1 are also known to impact follicular development and ovarian steroid levels in other species, but these relationships in mares are not established.
• The study hypothesizes that mares experience age-related declines in GH and IGF-1, which may correlate with ovarian steroids such as estradiol (E) and progesterone (P).

Methods

• Blood samples were collected from 56 healthy Spanish Purebred mares undergoing normal reproductive cycles.
• The mares were divided into four age groups: 6-9 years, 10-13 years, 14-16 years, and over 16 years.
• Concentrations of GH, IGF-1, estradiol-17β (E), and progesterone (P) were measured in all samples.
• Statistical analyses assessed differences among age groups and correlations between hormones.

Key Findings

• GH levels declined with age:
  • Mares aged 6-9 and 10-13 years had significantly higher GH levels compared to those 14-16 and over 16 years.
  • Mares 14-16 years also had higher GH than mares over 16 years.
• IGF-1 levels were significantly lower only in mares over 16 years compared to all younger groups.
• Ovarian steroid hormones (E and P) showed no significant differences across the different age groups.
• No correlation was found between GH and IGF-1 or between these somatotropic hormones and the ovarian steroids E and P.

Interpretation and Conclusions

• The study confirms that in mares, GH declines steadily with advancing age starting from middle age, while IGF-1 decline is significant mainly in very old mares (>16 years).
• The lack of change in ovarian steroid hormones suggests that reproductive hormone patterns remain stable despite the reduction in somatotropic axis activity.
• No direct correlation between GH, IGF-1, and ovarian steroids indicates that these hormone systems may operate independently in mares during aging.
• Reduced GH and IGF-1 levels can be considered as biomarkers of age-associated functional decline in mares, particularly reflecting somatotropic axis activity rather than changes in ovarian steroid hormone production.
• These findings contribute to understanding physiological aging in mares and could help in managing the health and reproduction of older horses.