Responses of blood glucose, insulin and cortisol concentrations to common equine diets.

This research investigates the effects of different horse diets on blood glucose, insulin, and cortisol levels. It found that cortisol levels fluctuated throughout the day, and the type of diet influenced insulin and glucose levels in the horses.

Experiments and Findings

The observation formed part of two main experiments:

• The first experiment was designed to explore the diurnal variation or variations that happen within a 24-hour period of glucose and two glucoregulatory hormones, insulin and cortisol, in four fasting geldings, i.e., castrated adult male horses. Against expectations, neither glucose nor insulin levels exhibited any kind of diurnal variation over 24 hours. However, cortisol levels did show fluctuations, displaying high values during the morning and low values in the evening – which is also known as a circadian rhythm.
• The second experiment delved into the response of glucose, insulin, cortisol, and selected amino acids to four different equine diets. Four 2-year-old quarter horse geldings were put on a Latin square design, a systematic layout for comparing the different diets. These diets were either 100% alfalfa, a 50-50 mix of alfalfa and corn, 100% corn, or 90% corn with 10% corn oil. All diets had the same digestible energy content. The horses were fed once following an overnight fast while blood samples were taken through a catheter in the jugular vein. Glucose levels did not vary according to the diet, except that the diets involving corn led to a considerable increase in glucose levels after eating. Insulin levels, on the other hand, did differ significantly depending on the diet. Yet, cortisol levels did not show any meal-related changes, instead sticking to the expected circadian rhythm.

Summary

Overall, the research indicates the impact of diet on some metabolic parameters in horses. The diets induced different responses in glucose and insulin concentrations, but cortisol levels remained consistent with its typical circadian rhythm, unaffected by diet. This information could play an important role in dietary planning for horses, particularly for those with metabolic disorders or sensitive glucoregulatory responses.