Short-term provision of moderate dietary starch alters fecal microbiota but does not exacerbate exercise-induced inflammation in yearling Quarter Horses.

Objective Summary

• This study investigated how short-term consumption of moderate amounts of dietary starch versus fiber impacts the fecal microbiota and exercise-induced inflammation in young Quarter Horses.
• The researchers tested if horses fed starch-based concentrates would experience greater inflammation after exercise compared to those fed fiber-based concentrates.

Introduction and Background

• Equine athletes often receive energy-dense feeds that are high in starch.
• High starch intake can change the gut microbiota in horses, potentially leading to systemic inflammation.
• The relationship between dietary starch, gut microbiome changes, and exercise-induced inflammation in horses is not fully understood.
• The study aimed to directly compare inflammatory responses in horses fed starch vs. fiber-based diets during exercise.

Methods

• Subjects: Yearling Quarter Horses averaging 16 months old and 337 kg in weight.
• Groups: Horses were divided into two groups:
  • CON (fiber-based control concentrate): 7 fillies, 8 geldings
  • STARCH (isocaloric, isonitrogenous starch concentrate): 8 fillies, 7 geldings
• Duration: Each horse was fed their respective diet for 24 days.
• Sample Collection:
  • Fecal samples for metagenomic analysis on days 0 and 21.
  • Blood samples for inflammatory mediators on days 0, 21, and during a 2-hour submaximal exercise test (SET) on day 22.
• Exercise Test: A controlled 2-hour submaximal exercise session to trigger potential inflammatory responses.

Results – Microbiota Changes

• By day 21, horses on the control fiber diet had higher levels of Lactobacillaceae bacteria (~5.7%) compared to starch-fed horses (~2.4%).
• Starch-fed horses had higher abundance of Lachnospiraceae bacteria (~38%) compared to fiber-fed horses (~32%).
• These findings indicate that dietary starch vs. fiber modulates the gut bacterial community structure.
• Despite these microbiome alterations, the diet alone did not significantly affect inflammatory markers before exercise.

Results – Exercise-Induced Inflammation

• C-reactive protein (CRP), an inflammation marker, increased significantly 24 hours after exercise in all horses.
• By 48 hours post-exercise:
  • CRP levels returned to baseline in starch-fed horses.
  • CRP remained elevated in fiber-fed horses, leading to higher CRP compared to starch group.
• Tumor necrosis factor-alpha (TNFα) behavior:
  • In starch-fed horses, TNFα increased at 1 hour post-exercise but returned to baseline by 6 hours.
  • In fiber-fed horses, TNFα increased later (at 24 hours) and remained elevated at 48 hours.
• Interleukin-10 (IL-10), an anti-inflammatory cytokine, was higher throughout exercise in fiber-fed horses compared to starch-fed horses.
• Other inflammation-related molecules like serum amyloid A (SAA), IL-4, IL-8, and vascular endothelial growth factor-A (VEGF-A) responded to exercise but were not influenced by diet type.

Conclusions and Implications

• Contrary to expectations, horses fed the fiber-based diet exhibited a stronger acute inflammatory response to exercise than those fed starch-based diets.
• The alterations in gut microbiota from different diets did not correspond with increased systemic inflammation in starch-fed horses.
• This suggests that moderate starch intake in young horses may not exacerbate exercise-induced inflammation as previously thought.
• Fiber-fed horses possibly mount a more robust immune response to exercise, highlighting complex interactions between diet, gut microbiota, and inflammation.
• These findings may impact feeding strategies for optimizing equine athlete health and performance.