Carbohydrate digestion in the stomach of horses grazed on pasture, fed hay or hay and oats.
Authors: Bachmann Martin, Schusser Gerald Fritz, Wensch-Dorendorf Monika, Pisch Caroline, Bochnia Mandy, Santo Milena Marie, Netzker Hanna, Woitow Gerhard, Thielebein Jens, Kesting Stefan, Riehl Gerhard, Greef Jörg Michael, Heinichen Karin, Zeyner Annette
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Gastric carbohydrate digestion in horses varies substantially depending on diet composition, according to this 2024 analysis of stomach contents from 23 horses fed pasture, hay alone, or hay with two levels of oat supplementation. Using acid insoluble ash as a marker of gastric transit, researchers found that oat starch underwent considerable breakdown in the stomach (44–29% reduction depending on feeding level), whilst simple sugars (glucose, fructose, sucrose) were largely cleared in forage-based diets but accumulated significantly when oats were fed at higher rates—suggesting saccharide absorption occurs primarily with lower grain loads. Fructan degradation predominated in pasture and hay diets (54–84% reduction, particularly in the non-glandular stomach region), yet was essentially absent in horses receiving the highest oat dose, indicating that elevated starch intake suppresses fermentation of these carbohydrates. These findings have important implications for understanding how ration composition reshapes the gastric microbial environment and metabolic responses; they suggest that high-concentrate feeding may alter the balance of carbohydrate fermentation in ways that could affect gastric pH, microbial populations and potentially predispose to digestive disturbance, making case for monitoring feeding rates and pasture access in performance horses.
Read the full abstract on PubMed
Practical Takeaways
- •Feeding high levels of oats (2 g starch/kg BW per meal) reduces carbohydrate digestion in the stomach compared to lower oat levels, potentially increasing undigested starch reaching the hindgut with metabolic consequences
- •Pasture and hay diets support greater fermentation of soluble carbohydrates and fructans in the non-glandular stomach, reflecting the natural digestive environment horses evolved to process
- •Diet composition significantly alters the gastric microbial environment and carbohydrate digestion patterns, which may influence overall digestive health and metabolic responses in working horses
Key Findings
- •Oat starch concentration in gastric digesta decreased by 44% in low-starch oat diet (OS1) and 29% in high-starch oat diet (OS2), with greater reduction in lower starch intake
- •Simple sugars (glucose, fructose, sucrose) disappeared from stomach more completely in pasture and hay-only diets compared to high-starch oat diet (OS2)
- •Fructan reduction was most pronounced in pasture (84% reduction) and hay (54% reduction) diets, occurring primarily in the non-glandular stomach and not occurring with high-starch diet
- •Evidence of fiber degradation was observed only in pasture-grazed horses, suggesting microbial activity varies significantly by diet type