| Popis: |
Summary Results are reported of the daily excretion of urine and feces, and their content of dry matter, crude fiber and nitrogen, from four dry, fasting cows, one fasting for a period of three days, one for periods of three and six days, and two others for a period of nine days. The results indicate that the bulk of the residual feed which is contained in the intestinal tract at the beginning of a fast is eliminated during the first two or three days after feeding, but that, in the absence of treatment directed toward the freeing of the alimentary tract from excreta, as in these experiments, the elimination of the same is incomplete even after nine days of fasting. The average daily nitrogen excreted in the urine during the last four days of the nine-day fasting periods, which is considered to represent, with fair accuracy, the protein katabolism of fasting, was 46.5 grams for one cow, and 43.6 grams for the other, per 1000 pounds live weight. These nitrogen values are equivalent to 0.62 pound, and 0.58 pound, of body protein, respectively, or 0.6 pound, as an average, per 1000 pounds live weight, which figure is identical with Armsby's published estimate (1) of the digestible crude protein maintenance requirement of cattle, and is 0.1 pound less than as in Morrison's standard (3) (0.7 pound), which may be considered as providing more liberally for reproduction and other exigencies of practice. It should be borne in mind, however, that the above values for protein katabolized during fasting may not represent the minimum protein requirement during feeding, in which case an abundant supply of non-nitrogenous nutriment may reduce the katabolism of protein to an amount less than that prevailing during fast. These figures for protein katabolism of fasting, therefore, when used as measures of the protein maintenance requirement during feeding, must be considered as providing a certain margin of safety. |
