A COMPARISON OF FIBROUS FEEDSTUFFS IN NON-RUMINANT RATIONS: EFFECTS ON GROWTH RESPONSES, DIGESTIBILITY, RATES OF PASSAGE AND INGESTA VOLUME

Abstract

Wheat bran, wheat straw, alfalfa, oat hulls, beet pulp, corn cobs and cellulose were added to basal diets at levels; of 8, 16, 24 and 32 per cent and, in a second experiment, at six levels of digestible energy to permit approximately isocaloric comparisons in the range of 2.2 to 3.4 digestible kilocalories per gram of feed dry matter. All diets were designed to be nutritionally adequate on the basis of nutrient content per unit weight of diet. Weanling mice were fed the diets during 14-day growth tests.Digestibility coefficients for the energy fraction were obtained: bran 42; wheat straw 0; alfalfa 37; oat hulls 10; beet pulp 41; corn cobs 14, and cellulose 0 per cent. Estimations of the digestibility of the basal ration by regression methods indicated associative effects, with corn cobs depressing basal digestibility from 89 to 85 per cent and beet pulp, alfalfa and oat hulls depressing it to about 86 per cent.Varied responses were obtained to isocaloric diets depending on the bulk source. For example, on diets containing 2.2–2.4 digestible Calories/gm., mice fed diets containing wheat straw often failed to survive, those fed diets containing beet pulp or cellulose did poorly, but gains of 70 per cent of normal were obtained when wheat bran or oat hulls was the diluent.Relative rates of passage of ingesta were computed by a method involving consideration of feed intakes, energy digestibility, maintenance requirements and weight gains over a fixed period. Bran rations had the highest passage rates; wheat straw, alfalfa and beet pulp the lowest. In vitro measurements indicated that the latter feeds were least capable of swelling in water and presumably occupied less space in the stomach. However, wheat straw and alfalfa tended to retain their physical characteristics throughout digestion.The results of these experiments emphasize the complexity and the importance in non-ruminant nutrition of the fibrous or bulk components of the ration as they influence available energy, feed intake, volume of ingesta at various levels in the gastrointestinal tract, rate of passage and microbial activity.