Dietary protein level and energy metabolism during treadmill exercise in horses.

This study evaluated the impact of dietary protein intake on horses’ metabolism and energy expenditure during exercise, concluding that the protein level in the diet does not significantly affect hepatic or intramuscular glycogen utilization, blood lactate levels, oxygen uptake, or plasma-free fatty acid levels in exercising horses.

Study Design and Methods

• The researchers used six trained Quarter Horse mares in a crossover experiment design. This design type involves each study participant undergoing every condition or treatment of the experiment, allowing their responses to be compared under different conditions.
• The mares were fed on either a 9.0% (control) or an 18.5% crude protein diet for a period of two weeks to adapt before the exercise testing. The diets represent a normal protein diet versus a high protein diet.
• Each horse then did an exercise test comprising a 15-minute treadmill run at a 11% grade, with a speed of 4.5 m/sec. The exercise was conducted 3-4 hours after a meal to ensure the absorption phase of digestion.
• Various types of blood samples (venous, arterial, and mixed-venous) were collected both at rest and during exercise, as well as muscle and liver samples. These samples allowed the researchers to measure various metabolites and analyze their changes in relation to dietary protein level and exercise.

Key Findings

• The dietary protein level did not have a significant effect on the usage of glycogen, a major energy storage form in the liver and muscles. This finding was robust regardless of the horse was at rest or engaging in exercise.
• Exercise in general elevated the lactate levels in the horses’ blood, muscle, and liver. Lactate is a metabolic byproduct of intense exercise when oxygen supply is limited. However, similar to the case with glycogen, the lactate levels were not found to be influenced by the protein content in diet.
• The control horses (on a normal protein diet) exhibited a higher lactate-to-pyruvate ratio in the venous blood. This ratio reflects the metabolic exchange between lactate and pyruvate, substances involved in energy production in the body. This might suggest that dietary protein level could subtly influence this metabolic intraconversion process, though more research would be needed to clarify this possibility.
• Dietary protein level also did not significantly affect oxygen consumption or plasma free fatty acid levels. Both factors can influence energy production and body fat regulation. However, both were found to increase with exercise.

Implications and Conclusions

• The study suggests that dietary protein does not majorly influence energy metabolism and substrate usage in horses during the absorptive phase of digestion, at least within the range of protein levels examined in this study.
• The data might hint at a possible connection between dieting and the conversion of lactate and pyruvate, but it is not conclusive, and more research is necessary to delve into this aspect.