Book Description

These experiments were designed to study the effect that feeding rations varying in energy and protein level had on energy and nitrogen digestibility and nitrogen retention by weanling rats and growing swine. A 2 x 2 factorial design using rations containing gross energy levels of 3.2 and 3.9 Cal./gm. and crude protein levels of 14 and 187. was used for the major studies. Rate of gain and efficiency of feed utilization by swine fed these rations from weaning to market weight, and carcass characteristics of the market swine were also studied. Twenty percent Terralite, a fine aggregate of vermiculite, was used to lower the digestible energy content of the rations. In the rat trial Terralite compared favourably with Alphacel, a non-nutritive cellulose, previously used as a diluent in studies of this nature with rats. The apparent digestibility of energy and nitrogen by rats and swine were similar. Although swine digestibility figures varied with the age of the pig, the average was near that obtained for weanling rats. Nitrogen digestibility decreased for both species when a diluent was used to lower the energy content of the ration. As the diets had energy-protein ratios below that required for maximum nitrogen utilization by rats, nitrogen retention as a percentage of gross or digestible nitrogen was low for all diets used in the rat trial. On the basis of nitrogen retention weanling pigs, however, required a higher level of protein in their ration than was required by weanling rats. In the trial with 15 lb. pigs the percent nitrogen retention was increased by raising the protein level of the ration. At later stages of growth nitrogen retention appeared to decrease when high levels of protein were fed. Rate of gain and feed efficiency in pigs from weaning to market weight were improved by feeding high levels of protein during early stages of growth, and by increasing the energy level of the ration at later stages. Feeding high levels of protein during the finishing period decreased rate of gain and efficiency of feed utilization. Carcass quality was not seriously affected by feeding high energy rations when they contained corresponding high levels of protein. However, pigs fed low energy rations did have the superior carcasses. During the later stages of growth male pigs made faster weight gains than females. Female pigs, however, excelled males in all carcass characteristics measured.