The effect of dietary protein level on exercising horses.

This research study examined how different levels of dietary protein impacted the metabolic response to exercise in horses, finding no negative effects from a high-protein diet on the horses’ metabolism during a short exercise on an inclined treadmill.

Study Overview

• The study used six mature Quarter Horse mares in a design called a crossover study. In this type of study, each participant acts as their own control group, by being exposed to both the test and control conditions. This design was chosen to assess the effect of dietary protein on the metabolic response to exercise.
• The horses were given two weeks to adapt to one of two diets: either the control diet with 12.9% crude protein (CP), or the high protein diet with 18.5% CP.
• After the adaptation period, each horse underwent the same standard exercise test. This test consisted of 15 minutes of exercise at a speed of 4.5 m/sec on a motorized treadmill positioned at a 9% incline.

Study Results

• The exercise resulted in an increase in heart rate for all horses, but there was no notable difference in heart rate between the horses on the control diet and those on the high-protein diet.
• In the jugular vein, lactate levels increased from 6.3 to 52.0 mg/ml in the control group and from 6.3 to 45.6 mg/ml in the high-protein group, indicating an interaction between diet and exercise for lactate.
• During exercise, plasma ammonia (NH3) levels also increased in all horses, but not until the 15th minute of the test. At this point, NH3 levels had increased more than four times over. Despite this rise, dietary protein level did not affect NH3 levels.
• However, blood urea nitrogen (urea-N), a by-product of protein metabolism, was significantly higher in the horses on the high-protein diet, indicating higher levels of protein metabolism.
• In regards to other metabolites, plasma alanine and glutamine, their levels also increased during the exercise, but they differed between the control and the high-protein groups

Study Conclusions

• The researchers concluded that there was no metabolic evidence for any detrimental effects of excess dietary protein on exercising horses. They observed no significant difference in heart rate, lactate levels, NH3 levels, or other metabolite levels that would suggest a negative metabolic response to exercise arose from a high-protein diet.
• The most notable difference between the diets was the higher levels of urea-N in the high-protein diet, which simply reflects that the horses metabolized more protein, as expected from the higher protein intake.