Transfer of blood urea nitrogen to cecal microbial nitrogen is increased by fructo‐oligosaccharide feeding in guinea pigs

The present study was conducted to determine the mechanism by which nitrogen ( N ) availability is improved by fructo‐oligosaccharide ( FOS ) in guinea pigs. Adult male guinea pigs were fed a commercial pellet diet (50 g/day) with either 5% glucose or 5% FOS for 7 days in individual metabolism cages. After 7 days of feeding the diet, 15 N ‐urea was administered intravenously 1 h before slaughter under anesthesia. The amount and concentration of total, protein, bacterial, ammonia and urea N and the 15 N atom % excess were measured in blood, liver, gut contents and urine. The 15 N atom % excess of total and protein N , and the amount of total, protein and bacteria N and 15 N in the cecum were significantly increased by the consumption of FOS . Furthermore, the concentration and amount of short‐chain fatty acids were significantly increased by the consumption of FOS . In contrast, the amount of urinary 15 N was significantly decreased by the consumption of FOS . These results suggest that consumption of FOS increases transfer of blood urea N into the large intestine for bacterial N synthesis, which is subsequently re‐absorbed by cecotrophy, and contributes to the increase of N utilization in guinea pigs.