Protein Nutrition and the Utilization of Dietary Protein at Different Levels of Intake by Growing Swine

Abstract

Six Hampshire pigs, weighing initially from 21 to 27 kg., were carried through five nitrogen metabolism periods on three different levels of the same protein mixture (soybean meal), approximately 4, 10 and 16 percent, and on two low-nitrogen standardizing diets, in periods 1 and 5, for the purpose of measuring the biological value of the protein at different levels of intake. The pig is readily adaptable to a very low-nitrogen diet, gaining in body weight for many weeks with the development of only a slight degree of hypoproteinemia. The fecal nitrogen output of the growing pig is linearly related to the protein level of the diet fed (on the dry basis), over a range of practically zero to 16 percent. Under the conditions of this experiment, the metabolic fecal nitrogen (the intercept of the regression line on the ordinate) was 0.91 gm. per kg. of dry matter consumed. The regression of urinary nitrogen on truly absorbed nitrogen, both variates being expressed to W_kg.^0.734 to permit pooling of the data for differences in body weight, is evidently rectilinear from 0 to 10 percent of protein, or somewhat higher.