METABOLIC FECAL NITROGEN IN RUMINANTS ESTIMATED FROM DRY MATTER EXCRETION

Relationships between dry matter (DM) and nitrogen (N) intakes and excretions were examined using digestibility data from 45 rations fed to sheep and cattle. The proportion of total variation due to regression was greater when N intake was expressed as a function of DM excretion than as a function of DM intake. Nitrogen excretion was expressed by the equation y = −0.021x2 + 0.137x + 0.891, where y = g N excretion per 100 g of fecal DM and x = g N intake per 100 g fecal DM. Extrapolating N excretion to zero N intake, the point of intercept at y = 0.891 g N per 100 g of fecal DM excretion is suggested as a measure of metabolic fecal nitrogen independent of the hay to concentrate ratio of the ration.

THE ENDOGENOUS URINARY AND METABOLIC FECAL NITROGEN EXCRETIONS OF NEWBORN DAIRY CALVES

Daily observations were made on the fecal and urinary nitrogen excretions of four calves fed nitrogen-free diets during the second and fifth weeks after birth. The endogenous urinary nitrogen excretion was equivalent to 65.3 mg. per kg. of body weight (W) per day or 186 mg. per kg. W0.72. The metabolic fecal nitrogen excretion averaged 44.0 mg. per kg. of body weight per day or 0.334 per cent of the dry matter intake.

THE METABOLIC FECAL NITROGEN EXCRETION OF THE PIG AS INFLUENCED BY THE AMOUNT OF FIBRE IN THE RATION AND BY BODY WEIGHT

Nitrogen balance experiments were carried out with growing Yorkshire barrows to determine the influence of level of fibre (5, 10, and 15 per cent wood cellulose) in the ration, and weight of pig (15, 30, 45, and 60 kg.) on the metabolic fecal nitrogen (M.F.N.) excretion. Semi-synthetic rations containing 0.3, 5.4, 9.4, 14.0, 18.0, and 22.0 per cent protein were fed. The source of the protein was a mixture of wheat, skimmilk powder, and fishmeal. M.F.N. by direct determination on the protein-low ration (0.3 per cent protein) was compared with M.F.N. determined by extrapolation to zero protein from the other rations.An increase in the level of fibre in the ration significantly (p < 0.01) increased the M.F.N. excretion and decreased the apparent and true digestibility of the protein but had no effect on the biological value (B.V.) of the protein. As the pigs increased in weight from 15 to 50 kg., the M.F.N. excretion, per 100 gm. dry matter (D.M.) consumed, decreased in proportion to the 0.3 power of body weight, the apparent digestibility of the protein increased, and the B.V. of the protein decreased. M.F.N, per 100 gm. D.M. consumed, apparent digestibility, and B.V. of the protein did not change significantly between body weights of 50 and 65 kg.There was no significant difference between M.F.N. determined by extrapolation to zero N intake and M.F.N. determined directly by feeding a protein-low (0.3 per cent protein) ration, when the rations contained the same percentage of cellulose. The M.F.N. (gm. per 100 gm. D.M. intake) for pigs weighing an average 37 kg. was 0.10, 0.13 and 0.14 for rations containing 5, 10, and 15 per cent cellulose, respectively.Since weight of pig and the level of fibre in the ration significantly influenced the M.F.N. excretion, the latter should be determined, either directly or by extrapolation, using rations of the same fibre content and pigs of the same body weight as are used in determining the true digestibility and B.V. of proteins.