Acute effects of short-term feed deprivation and refeeding on circulating concentrations of metabolites, insulin-like growth factor I, insulin-like growth factor binding proteins, somatotropin, and thyroid hormones in adult geldings.

This study explores the short-term effects of food deprivation and refeeding on various hormones and metabolites in adult geldings. The research highlights how changes in food intake affect the secretion of thyroid hormones, somatotropin, and possibly Insulin-like Growth Factor I, a process which helps maintain the horse’s physiological balance.

Objective and Methodology

• The research was conducted on Standardbred geldings aged 7 to 21 years, and aimed to identify the sequence of changes in plasma concentrations of certain hormones and metabolites during 48 hours of feed deprivation and 12 hours after refeeding.
• The plasma concentrations of hormones and metabolites were determined with methods specifically validated for horse plasma. Insulin-like Growth Factor Binding Proteins (IGFBP) were determined using a radioligand analysis after SDS-PAGE electrophoresis, a common biochemical method used to study protein mixtures.

Findings

• The study found that the plasma concentrations of triiodothyronine and thyroxine (thyroid hormones) decreased significant (p<0.01) during feed deprivation and increased (p<0.01) upon refeeding.
• Plasma glucose and Insulin-like Growth Factor I (IGF-I) either decreased or did not change during feed deprivation.
• In contrast, plasma concentrations of NEFA (Non-esterified Fatty Acids) and urea nitrogen showed an increase (p<0.01) during feed deprivation and decreased (p<0.01) during the refeeding period.
• Plasma somatotropin (ST), a growth hormone, increased around 80% at 24 to 36 hours of feed deprivation, returned to control values at 48 hours of feed deprivation, increased almost three times 3 hours after refeeding, and then returned to control values 6 hours after refeeding.
• Five Insulin-like Growth Factor Binding Proteins were identified, but their plasma concentrations did not significantly alter during feed deprivation or after refeeding.

Conclusion

• The findings suggest that changes in nutrient availability due to feed deprivation and refeeding alter the secretion of thyroid hormones, somatotropin (ST), and potentially IGF-I.
• These adaptive changes play an important role in maintaining homeostasis – the stable state of physiological balance – in horses.