Digestion and nitrogen metabolism in sheep and red deer given large or small amounts of water and protein

1. The interaction between nitrogen and water intake was studied in two ewes and two red deer hinds. They were given pelleted diets, at maintenance level, containing equal amounts of roughage but either rich or poor in nitrogen. The deer received 50 % more food than the sheep. Water was given either in large amounts (sheep 5.01, deer 7.0 1 daily) or in small amounts (sheep 1.1 l, deer 2.4 l daily).2. Nearly three-quarters of the nitrogen of the high-nitrogen rations but less than half of that of the low-nitrogen rations was excreted in the urine. Restriction of water intake reduced urinary nitrogen excretion by only about 1 g daily, mainly as a result of decreases in the excretion of urea and ammonia, but did not affect the excretion of nitrogen in the faeces.3. The urinary excretions of creatinine, creatine, hippuric acid, uric acid and allantoin were also examined. The excretion of creatinine was not related to either nitrogen or water intake. The excretion of uric acid and of allantoin was greater in the sheep than in the deer.4. The concentrations of urea in the plasma and of ammonia in the rumen fluid were measured before and after feeding. The plasma urea value was related to dietary nitrogen intake and was higher on the low- than on the high-water regime. The rumen ammonia value also was related to the nitrogen intake but, while it generally increased after feeding when the high-nitrogen diet was given, it fell almost to zero 2 h after feeding when the low-nitrogen diet was given.5. The sheep digested dry matter, cellulose and nitrogen a little more fully than the deer. The high-water regime slightly increased the digestibility of dry matter and cellulose but did not affect the digestibility of nitrogen.