Effects of dietary energy supply on serum thyroxine, tri-iodothyronine and insulin concentrations in young horses.

The study examined the effects of meal consumption on the circulating concentrations of growth-regulating hormones in young Thoroughbred horses. Results suggested that the dietary energy supply influenced the horses’ serum levels of thyroxine (T4), tri-iodothyronine (T3) and insulin.

Objective of the Study

• The objective of the research was to investigate the effects of the dietary energy supply on the concentration levels of the growth-regulating hormones thyroxine (T4), tri-iodothyronine (T3), and insulin in young thoroughbred horses. This was done by comparing how meal ingestion influences the hormone levels across three distinct dietary energy levels; 70% (A), 100% (B), and 130% (C) of the energy and protein requirements of the horses.

Key Findings of the Study

• The peak insulin concentrations were observed at 1, 2, and 3 hours after ingestion of diets C, B, and A respectively.
• Increases in plasma glucose concentrations were noted before the rise in serum insulin concentrations.
• For serum thyroxine or T4 concentrations, an increase was seen after eating diets A and B, a drop after eating diet C.
• In contrast, serum T3 concentrations didn’t change after eating diet A but showed an increase after consuming diets B and C. This spike was more significant and faster in horses fed diet C.
• The drop in T4 concentration after consuming diet C was five times greater than the increase in T3 concentration.
• A meal high in energy (carbohydrate) content, sped up insulin secretion and resulted in reduced T4 secretion and accelerated T4 conversion to T3.
• Nonetheless, six months later, the serum T4 and T3 concentrations were not influenced by meal ingestion.

Implication and Conclusion of the Study

• The findings of the study suggest that the dietary energy supply impacts the circulating hormones in young Thoroughbred horses, altering their insulin, T3 and T4 levels.
• Although the rise in insulin secretion and hormonal changes was seen immediately after meal consumption, these effects were not permanent, as indicated by the fact that after six months, the hormone levels were unchanged by meal ingestion. This could suggest adaptability in the digestive and metabolic systems of the horses.