The effects of increased nitrogen intakes on plasma urea nitrogen and rumen ammonia levels in sheep

A series of five roughage rations providing increasing amounts of nitrogen (6.8, 16.8, 23.5, 37.3, and 46.3 g/day) and some changes in dry matter intakes (720, 710, 704, 1056, and 1408 g/day) was offered to sheep. The first four rations were given hourly and the fifth ad libitum. Urine outputs, urine total nitrogen, urine urea nitrogen, and urea clearance values increased with nitrogen intakes. Water intakes were linearly related to dry matter intakes. Plasma urea nitrogen and rumen ammonia levels both increased linearly to about 30 mg/100 ml, but did not increase further on higher levels of nitrogen intake. At these levels of intake both plasma urea nitrogen and rumen ammonia levels were no longer related to urine nitrogen excretion rates. The results are discussed in relation to the role of the kidney tubules in nitrogen excretion in the sheep.