Nitrogen digestion and urea recycling in H okkaido native horses fed hay‐based diets

Nitrogen ( N ) digestion and urea‐ N metabolism in H okkaido native horses fed roughage‐based diets containing different types and levels of protein sources were studied. Horses (173 ± 4.8 kg) fitted with an ileum cannula were fed four diets consisting of 100% timothy hay ( TH ), 88% TH and 12% soybean meal ( SBM ), 79% TH and 21% SBM , and 51% TH and 49% alfalfa hay at 2.2% of body weight. Dietary protein content varied from 5% to 15% of dry matter. Apparent N digestibilities in the pre‐cecum and total tract for the TH diet were lower than those for other diets. However, the proportion of post‐ileum N digestion to N intake was not affected by the diets. Urea‐ N production was linearly related to N intake, but gut urea‐ N entry was not affected by the diets. The proportion of gut urea‐ N entry to urea‐ N production tended to be higher for the TH diet (57%) than the two SBM diets (39%). Anabolic use of urea‐ N entering the gut was not affected by the diets (20–36% of gut urea‐ N entry). These results indicate that urea‐ N recycling provides additional N sources for microbial fermentation in the hindgut of H okkaido native horses fed low‐quality roughages.