Phytate and phosphorus movements in the digestive tract of horses

This experiment was conducted to study phytate degradation and the effect of dietary phytate level on phosphorus absorption in the gastrointestinal tract of horses. Six Thoroughbred horses were fed diets containing low-phytate diet or high-phytate diet for 5 days. The diets were supplemented with Cr2O3 as an unabsorbable marker. The horses were killed 3 h after the last feeding and digesta in some segments of the intestine were collected. In both dietary groups, the daily passage of phytate phosphorus was decreased in the upper small intestine and in the lower large intestine. The daily passage of phytate phosphorus in the lower large intestine did not differ between these groups. Although the passage of total phosphorus increased in the upper small intestine and in the upper large intestine of both groups, its passage decreased in the lower large intestine. These results suggest that phytate phosphorus is degraded in the upper small intestine and in the lower large intestine of both groups. Phosphorus is suggested to be mainly absorbed in the lower large intestine. Therefore, phytate phosphorus is considered to be easily absorbed in horses because the major site of phosphorus is the lower large intestine where most of phytate is already degraded.