Effects on exercise response, fluid and acid-base balance of protein intake from forage-only diets in standardbred horses.

This research explores the impact of high protein (HP) intake from forage-only diets on nitrogen balance, fluid balance, acid-base balance, and exercise reaction in race-ready Standardbred horses. The findings indicate that an excessive protein intake alters fluid and acid-base balance and increases nitrogen excretion in horses, which may potentially challenge horses during extended exercise.

Study Design and Methods

• The study was conducted using a crossover design, with two diets based on high-energy grass forage fed to six Standardbred horses in racing condition over 23 days. These diets differed mainly by their crude protein (CP) percentage: one with a high CP intake (16.6%) and one with the recommended CP intake (12.5%) for racehorses.
• The horses were subjected to both intensive exercises twice a week and slow exercises one to three times a week. Several biological variables were monitored to assess the horses’ health and response to the diets.
• Faeces and urine were collected at the start and end of each trial period and analyzed for dry matter, pH, and nitrogen contents. Other measurements taken included heart rate, respiratory rate, and blood analysis before, during, and after the exercises. Specific blood components measured were sodium, potassium, chloride, total plasma proteins, TCO2, urea, pH and lactate. The strong ion difference was also calculated.

Study Outcomes

The results demonstrated several impacts of a high protein intake from a forage-only diet.

• The HP diet resulted in a decrease in urinary pH, indicating a disruption in acid-base balance within the body.
• There was an increase in nitrogen excretion, suggesting that the HP diet led to an unnecessary nitrogen load that had to be eliminated from the body.
• Increased intake of water, more significant urine volume, and higher faecal water content were observed with the HP diet, suggesting alterations to fluid balance in the body.
• Despite these changes, exercise-related responses such as heart rates, respiratory rates, and various blood markers (including sodium, potassium, chloride, and lactate levels) didn’t significantly vary between the two diets.

Conclusions

• In summary, this study suggests feeding horses a forage-only diet with a high protein intake, at around 160% of the recommended dietary requirement, caused increased nitrogen excretion and alterations to both fluid and acid-base balance.
• The consequences of these changes potentially pose unnecessary challenges for horses undertaking prolonged exercise.
• However, this high protein intake did not significantly impact the horses’ physiological response to exercise in the short term.