Amount of concentrated feed appears to increase muscle enzyme leakage in horses in training

In this study, the researchers visited Swedish professional racehorse trainers who were selected because they had different feeding strategies, varying in the levels of starch-rich concentrates they provided to their horses. Most Standardbred trotters perform high-intensity exercise twice a week when they are trained with a heart rate above 200 beats per minute. Samples were taken from 76 horses after performing high-intensity exercise. The horses were divided into three groups based on starch allowance per day.

The starch in concentrates is one of the nutrients that horses metabolise and use for energy.

After the high-intensity exercise, the horses that received the least concentrate had the lowest levels of muscle enzyme activity in their blood plasma, indicating muscle cell damage. This suggests that leakage from muscle fibers was lower in the horses that received the least amount of concentrated feed, even though they trained equally hard.

The researchers don't know why this is, but it may be related to higher oxidative stress, or higher lactic acid levels during exercise,- something that previous studies have shown is also associated with high starch intake.

Differences between horses of different sex

In the study, starch allowances were on average lower in mares than in stallions and geldings. Despite this, mares had higher levels of muscle enzyme activity after exercise. Previous studies have shown that mares are at higher risk of developing muscle problems than stallions and geldings, which seems to be supported by these results.

Based on this study, it appears that no or low starch intake minimizes muscle damage after exercise. This is important knowledge that can be used to promote horse health during exercise and improve welfare for athletic horses.

References:

Connysson, Malin, och Anna Jansson. 2025 ”Starch Allowance and Muscle Enzyme Activity in Healthy Standardbred Trotters Trained by Professional Trainers”. Journal of Animal Physiology and Animal Nutrition https://doi.org/10.1111/jpn.14127.