According to Gram Research analysis, a 2026 study of 30 young Quarter Horses found that those fed a starch-based concentrate actually had less inflammation 48 hours after exercise compared to horses fed a fiber-based diet, despite the starch diet altering their gut bacteria. This contradicts the common belief that starchy feeds increase exercise-related inflammation in athletic horses, suggesting that moderate starch levels may be acceptable for young athletic horses when calories and protein are controlled.
Researchers studied whether feeding young Quarter Horses a starch-based diet would increase inflammation after exercise, compared to a fiber-based diet. Over 24 days, one group ate starch concentrate while another ate fiber concentrate. While the starch diet did change the bacteria in horses’ digestive systems, it actually resulted in less inflammation after exercise than the fiber diet. This surprising finding challenges the common belief that starchy feeds are bad for athletic horses, suggesting that the type of feed may matter less than previously thought for managing exercise-related inflammation.
Key Statistics
A 2026 research article of 30 young Quarter Horses found that fiber-fed horses had elevated CRP (inflammation marker) at 48 hours post-exercise while starch-fed horses returned to normal, demonstrating less post-exercise inflammation in the starch-fed group.
In the same 2026 study, starch-based feeding altered gut bacteria composition, reducing beneficial Lactobacillaceae from 5.7% to 2.4% and increasing Lachnospiraceae from 32% to 38%, yet these microbiome changes did not increase exercise-induced inflammation as hypothesized.
A 2026 equine study of 30 Quarter Horses showed that TNFα (inflammation marker) spiked at 1 hour post-exercise in starch-fed horses then normalized by 6 hours, while fiber-fed horses maintained elevated TNFα at 24 and 48 hours, indicating prolonged inflammatory response.
Research published in 2026 involving 30 young Quarter Horses demonstrated that fiber-fed horses maintained higher IL-10 (anti-inflammatory marker) throughout exercise testing compared to starch-fed horses, suggesting a more robust overall inflammatory response to exercise stress.
The Quick Take
- What they studied: Whether feeding young athletic horses a starch-based diet would cause more inflammation in their bodies after exercise compared to a fiber-based diet.
- Who participated: 30 young Quarter Horses (average age 16 months, average weight 337 kg) split into two groups: 15 eating fiber-based feed and 15 eating starch-based feed.
- Key finding: Horses eating the starch-based diet actually had less inflammation 48 hours after exercise than horses eating the fiber-based diet, despite the starch diet changing their gut bacteria.
- What it means for you: If you own athletic horses, starch-based feeds may not be as problematic for post-exercise inflammation as previously believed. However, this study was short-term (24 days) and used young horses, so consult your veterinarian before making feed changes for your specific horse.
The Research Details
Researchers divided 30 young Quarter Horses into two equal groups. One group received a fiber-based concentrate (the control group), while the other received a starch-based concentrate with the same calories and protein content. Both diets were fed for 24 days. The researchers collected stool samples on day 0 and day 21 to analyze the bacteria living in each horse’s digestive system. On day 22, all horses completed a 2-hour exercise test at moderate intensity. Blood samples were taken before exercise, then at 1 hour, 6 hours, 24 hours, and 48 hours after exercise to measure inflammation markers.
This study design is called a controlled feeding trial because researchers carefully controlled what each horse ate and measured specific outcomes. By using two diets with identical calories and protein, the researchers could isolate the effect of starch versus fiber. The exercise test was standardized so all horses experienced the same physical stress, allowing fair comparison of how their bodies responded.
This research approach is important because it mimics real-world conditions for athletic horses while maintaining scientific control. Rather than just looking at bacteria or inflammation separately, the researchers measured both to understand the complete picture. The standardized exercise test ensures that any differences in inflammation between groups are due to diet, not differences in exercise intensity. This type of study provides stronger evidence than simply observing horses in their natural environment.
This study has several strengths: it used a controlled design with equal group sizes, measured multiple inflammation markers rather than just one, and collected samples at multiple time points to track changes over time. The sample size of 30 horses is reasonable for this type of research. However, the study lasted only 24 days, which is relatively short for evaluating long-term dietary effects. The horses were all young (around 16 months old), so results may not apply to adult or older horses. The study was published in a peer-reviewed journal, meaning other experts reviewed the methods and findings before publication.
What the Results Show
The most surprising finding was that horses eating the starch-based diet had less inflammation after exercise than horses eating the fiber-based diet. Specifically, a marker called CRP (C-reactive protein) increased in all horses 24 hours after exercise, but by 48 hours, it returned to normal in starch-fed horses while remaining elevated in fiber-fed horses. Another inflammation marker called TNFα showed a similar pattern: it spiked quickly in starch-fed horses (at 1 hour) then returned to normal by 6 hours, but in fiber-fed horses it remained elevated at 24 and 48 hours after exercise.
The starch diet did change the bacteria in horses’ digestive systems as expected. Horses eating starch had less of a beneficial bacteria called Lactobacillaceae (2.4% versus 5.7% in fiber-fed horses) and more of another bacteria called Lachnospiraceae (38% versus 32% in fiber-fed horses). However, diet alone did not cause inflammation before exercise—the inflammation differences only appeared after the exercise test.
Interestingly, fiber-fed horses had higher levels of IL-10, an anti-inflammatory substance, throughout the exercise test compared to starch-fed horses. This suggests their bodies were mounting a stronger overall inflammatory response to the exercise stress.
Several other inflammation markers were measured but showed no significant differences between diet groups: SAA, IL-4, IL-8, and VEGF-A. These markers did respond to the exercise test in both groups, but the diet type did not influence their response. This suggests that while starch and fiber diets affect some inflammation markers differently, they don’t affect all inflammatory responses equally.
This finding contradicts the common assumption in equine nutrition that starch-based feeds promote systemic inflammation in athletic horses. Many previous studies and industry practices have recommended limiting starch for athletic horses based on concerns about inflammation. However, this research suggests that a moderate amount of starch in an isocaloric (same-calorie) diet may not be problematic for exercise-induced inflammation in young horses. The altered gut bacteria from starch feeding did not translate into increased inflammation as the researchers initially hypothesized. This aligns with emerging research suggesting that the relationship between diet, gut bacteria, and inflammation is more complex than previously understood.
This study has several important limitations. First, it lasted only 24 days, which is relatively short for evaluating dietary effects on the microbiome and inflammation. Long-term effects might differ from short-term effects. Second, the study used only young horses (average 16 months old), so results may not apply to adult or senior horses whose digestive systems and immune responses differ. Third, the exercise test was moderate intensity for 2 hours; results might differ with higher-intensity exercise or different exercise durations. Fourth, the study measured inflammation markers in blood but did not assess gastrointestinal health directly, so we don’t know if the altered microbiome affected digestive function. Finally, the sample size of 30 horses, while reasonable, is relatively small, so results should be confirmed in larger studies before making broad recommendations.
The Bottom Line
Based on this research, moderate amounts of starch in horse feed do not appear to increase exercise-induced inflammation in young horses, contrary to previous concerns. However, this is a single short-term study, so recommendations should be moderate in confidence. Consult with an equine veterinarian or nutritionist before significantly changing your horse’s diet. If your horse is young and athletic, a starch-based concentrate may be acceptable if it provides adequate calories and protein. Monitor your horse’s digestive health, coat condition, and exercise recovery regardless of feed type. This research does not mean starch is ideal for all horses—individual horses may respond differently.
Horse owners with young athletic Quarter Horses (or similar breeds) may find this research relevant when choosing between starch-based and fiber-based concentrates. Equine nutritionists and veterinarians should consider this finding when counseling clients about feed selection for athletic horses. However, this study does not apply to horses with existing digestive problems, metabolic disorders, or those prone to inflammation. Owners of older horses should seek additional research before applying these findings, as aging may change how horses respond to different feed types.
Changes in gut bacteria appeared within 21 days of dietary change. Inflammation responses to exercise were measured within 48 hours of the exercise test. If you were to change your horse’s diet based on this research, you might expect to see changes in digestive bacteria within 2-3 weeks, but the full effects on exercise recovery might take longer to evaluate. Plan to observe your horse for at least 4-6 weeks when making dietary changes to assess overall effects on performance and health.
Frequently Asked Questions
Is starch bad for athletic horses?
A 2026 study of 30 young Quarter Horses found that starch-based feed did not increase exercise-induced inflammation compared to fiber-based feed. In fact, starch-fed horses recovered faster from inflammation markers after exercise. However, this was a short-term study in young horses, so individual responses vary—consult your veterinarian about your specific horse.
Does changing horse feed affect their gut bacteria?
Yes. The 2026 study showed that switching to starch-based concentrate changed gut bacteria composition within 21 days, reducing beneficial Lactobacillaceae and increasing Lachnospiraceae. However, these bacterial changes did not automatically cause inflammation, suggesting the relationship between diet, bacteria, and health is more complex than previously thought.
How long does it take to see effects from changing horse feed?
Gut bacteria changes appear within 2-3 weeks of dietary change, as shown in the 2026 study. However, effects on exercise recovery and overall health may take 4-6 weeks to fully evaluate. Monitor your horse’s digestion, energy, and performance during this adjustment period.
What inflammation markers should I monitor in my athletic horse?
The 2026 research measured CRP and TNFα as key inflammation markers. However, blood tests require veterinary involvement. More practically, monitor your horse’s post-exercise recovery time, appetite, and any signs of stiffness or soreness 24-48 hours after workouts as indirect indicators of inflammation.
Can I feed my horse starch if they exercise regularly?
According to the 2026 study, moderate starch in an isocaloric diet did not increase exercise-induced inflammation in young athletic horses. However, this single study is not definitive for all horses. Work with your equine veterinarian or nutritionist to determine appropriate starch levels based on your horse’s age, metabolism, and individual response.
Want to Apply This Research?
- Track your horse’s post-exercise recovery metrics: record heart rate recovery time (how quickly heart rate returns to normal after exercise), appetite within 2 hours of exercise, and any signs of stiffness or soreness 24-48 hours after workouts. Compare these metrics before and after any feed changes.
- If using a nutrition tracking app, log your horse’s concentrate type (starch-based vs. fiber-based) and exercise intensity daily. After 3-4 weeks, review whether your horse’s recovery metrics improved, stayed the same, or worsened. This personal data helps determine if your individual horse responds well to the current feed.
- Set weekly reminders to assess your horse’s overall condition: coat quality, energy level, digestive health (manure consistency), and exercise performance. Create a simple scoring system (1-5 scale) for each metric and track trends over 8-12 weeks. This long-term approach reveals whether feed changes produce meaningful benefits for your specific horse, since individual responses vary.
This article summarizes research findings and is not a substitute for professional veterinary or equine nutritional advice. Individual horses respond differently to dietary changes based on age, metabolism, health status, and exercise intensity. Before making significant changes to your horse’s feed, consult with a licensed veterinarian or equine nutritionist who can evaluate your specific horse’s needs. This study was conducted in young Quarter Horses over 24 days; results may not apply to older horses, different breeds, or longer-term feeding. Do not use this information to diagnose or treat equine health conditions.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.