Molecular characterisation of carbohydrate digestion and absorption in equine small intestine.
Authors: Dyer J, Fernandez-Castaño Merediz E, Salmon K S H, Proudman C J, Edwards G B, Shirazi-Beechey S P
Journal: Equine veterinary journal
Summary
# Editorial Summary Horses depend substantially on small intestinal carbohydrate digestion and absorption for metabolisable energy, yet excessive dietary carbohydrates that overwhelm intestinal capacity pass into the hindgut where they disrupt microbial populations and precipitate gastrointestinal disease—a problem this 2002 study addressed through molecular investigation of the brush-border mechanisms responsible for carbohydrate handling. Using tissue samples from the equine small intestine, the researchers characterised the expression patterns of key disaccharidases (sucrase, lactase and maltase) and identified that glucose absorption occurs primarily via a high-affinity, low-capacity sodium-glucose cotransporter (SGLT1), with transport capacity declining significantly from duodenum through jejunum to ileum. The authors cloned equine SGLT1, confirming 84–87% amino acid identity with the transporter in other species, and demonstrated that mRNA abundance correlated directly with functional protein levels along the intestinal length, indicating that proximal intestine dominates glucose uptake in horses fed conventional grass-based diets. For equine practitioners, these findings provide a molecular foundation for understanding why grain-heavy or high-starch supplementation risks overwhelming the horse's actual digestive capacity—particularly in the proximal small intestine—and support the practice of conservative feeding strategies; the work also has implications for dietary management in horses recovering from colic surgery or intestinal resection, where absorptive capacity may be compromised.
Read the full abstract on PubMed
Practical Takeaways
- •Dietary carbohydrate loads exceeding the small intestine's digestive capacity (particularly the duodenum and jejunum) will reach the hindgut, disrupting microbial populations and increasing disease risk—manage grain and concentrate portions accordingly
- •The equine small intestine has limited carbohydrate absorption capacity compared to many other species; feed management strategies should reflect this anatomical constraint to prevent colic and related gastrointestinal disorders
- •In horses recovering from intestinal resection, glucose absorption may be further compromised; careful dietary design and potentially pharmaceutical support for carbohydrate digestion should be considered
Key Findings
- •Equine small intestine expresses disaccharidases (sucrase, lactase, maltase) diversely along its length with glucose transported via high-affinity, low-capacity SGLT1 cotransporter
- •Glucose absorption capacity is highest in duodenum, intermediate in jejunum, and lowest in ileum
- •Equine SGLT1 shares 84-87% amino acid identity with SGLT1 in other species and expression correlates with mRNA abundance
- •Proximal small intestine is the major site of glucose absorption in horses on grass-based diets, with expression regulated at mRNA level