Site of phosphorus absorption from the intestine of the horse.

The research sought to understand where in the horse’s digestive tract phosphorus is primarily absorbed. The findings indicate this occurs mainly from the large intestine, specifically the dorsal large colon and small colon, and is not affected by the type of feed consumed or calcium content.

Methodology:

• The researchers investigated the absorption site of phosphorus by comparing the absorption levels of 32P (a radioactive form of phosphorus) placed directly into the cecum of fistulated ponies versus levels absorbed from an intragastric dose.
• In another test, they measured apparent absorption in various parts of the pony’s intestinal tract using chromium oxide (Cr2O3) as an unabsorbable marker. This marker would pass through the digestive system without being absorbed, facilitating the identification of the areas where absorption occurred.

Findings:

• The research found no difference in the absorption of 32P following gastric or cecal administration. This suggests that phosphorus can be absorbed from the large intestine in horses.
• The findings also indicated that phosphorus was secreted into the upper half of the small intestine, with nearly an equal amount being absorbed from the lower half.
• There was a significant movement of phosphorus into the cecum, followed by absorption from the dorsal colon and the small colon.
• The key locations for net phosphorus absorption from all feed sources were the dorsal large colon and the small colon. This means that these are the primary areas where more phosphorus is absorbed than secreted.
• Interestingly, the type of feedstuff the horses consumed, or the calcium content within it, did not affect where the phosphorus absorption took place.

Implications:

• Understanding where in the digestive tract phosphorus is absorbed can help in managing equine nutrition and health. It provides insights into the nutrient requirements and dietary benefits of horses.
• As feed type and calcium content don’t influence the phosphorus absorption, these results have important implications for the formulation of horse diets.