Researchers have determined supplementing horses’ diets with protein within a short but safe timeframe after exercise might help them build muscle mass more than providing the same supplement at regular mealtimes.

A high-protein snack—given as soon as the horse is resting again—could add critical amino acids to the bloodstream when muscles need them for repair and damage control, said Patty Graham-Thiers, PhD, professor and department head of the equine studies program at Emory & Henry University, in Virginia.

In a previous study Graham-Thiers and her colleagues found that supplementing young and even senior horses’ diets with amino acids helped improved their muscle mass—which horses naturally lose with advancing age. It made her wonder whether the supplements might be even more useful if they’re provided right when the body needs them most, shortly after exercise.

“In humans it’s common to consume protein post-exercise to help with muscle mass recovery and development, especially in body builders,” she said. “So, I thought, what if amino acids are delivered (to horses) after exercise when the body is recovering and needs amino acids, either for repair or development of muscle tissue?”

Feeding Horses a High-Protein Supplement After Exercise

To find out, Graham-Thiers and Kristen Bowen, BA, an equine exercise and nutrition research assistant at Emory & Henry, tested the effects of supplementation timing on eight healthy adult riding school horses. The horses participated in light to moderate maintenance exercise one to two hours per day, five days per week for 12 weeks.

Caregivers provided all the horses morning and evening meals consisting of grass hay, textured feed, and corn. In addition, the animals consumed a daily high-protein pellet made of 32% crude protein.

Half the horses received the protein supplement split into their two daily meals, while the other half received the supplement about 20 minutes after exercise—once their heart rates, breathing, and body temperatures dropped to regular resting levels. On rest days without exercise, these four horses ate their protein pellets as a separate midday snack.

The team collected urine and feces from each horse for four days before and after the 12-week experiment. They also took blood samples at the start and end of the study period, which they drew immediately after exercise and one and three hours later.

Studying the Effects of Feeding Timing on Muscle Health

The researchers used the urine and fecal samples to calculate nitrogen balance. Blood plasma samples allowed them to measure amino acid concentrations, albumin, plasma urea N (PUN), creatine kinase (CK), and creatinine.

The results of these tests revealed horses receiving supplementation in their meals had higher plasma concentrations of amino acids than those receiving the supplement shortly after exercise. The researchers explained this is likely because the horses had consumed more protein before exercise than the others, which had not yet had their daily protein pellets.  

The horses receiving the supplement after exercise had rising amino acid concentrations at the one-hour and three-hour post-exercise readings—likely reflecting a beneficial amino acid pool, the team said. The other horses’ amino acid concentrations, meanwhile, dropped.

Additionally, horses receiving the supplement just after exercise retained nitrogen better, which suggests they might have a timelier supply of proteins and amino acids for muscle protein repair and development.

The post-exercise supplementation group also had higher creatinine levels (a known marker of muscle mass) in their plasma. And they had less creatine kinase—an indicator of muscle protein damage or breakdown. This suggests horses might have been recovering faster after exercise than the other group, the researchers said.

Combined, the findings suggest feeding horses a high-protein meal shortly after exercise could help boost levels of circulating amino acids, which could aid muscle protein development while protecting against muscle protein breakdown.Even so, Graham-Thiers said more research is necessary before she and her colleagues can offer concrete supplementation guidelines.

Take-Home Message

“Ideally, I would suggest providing a small high-protein meal when it is safe to do so after exercise,” she noted. “However, this is not always practical. I would encourage riders to be aware of the time frame between feeding and exercise; the longer that time has been, the more important it might be for recovery to offer a small high-protein meal after exercise.”

The study, ”Timing of feeding a protein supplement on nitrogen balance and plasma amino acids during exercise recovery in horses,” appeared in the Journal of Animal Physiology and Animal Nutrition in July 2024.