INGREDIENT AND PROCESSING INTERRELATIONSHIPS IN SWINE FEEDS: I. EFFECTS OF ANTIBIOTICS, PROTEIN SOURCE AND WHEAT BRAN ON THE RESPONSES TO PELLETED FEED

A swine feeding trial, of 2 × 2 × 2 × 2 factorial design, involving 64 pigs (32 gilts and 32 barrows) weighing initially 50 ± 2 pounds and fed to a final weight of 110 ± 2 pounds was carried out. The dietary variables were meal vs. pellets, 0 vs. 10 per cent wheat bran, mixed animal-plant vs. all-plant origin protein supplement and 0 vs. 33 p.p.m. of an antibiotic mixture (penicillin, streptomycin and chlortetracycline). Weight gains and feed intakes were recorded bi-weekly and a Cr2O3-marker digestion trial was imposed on 32 pigs during the feeding test.The results revealed distinct interrelationships among all four experimental variables that prevailed through to the highest order statistical interaction. Consequently discussion in this paper was restricted to those factors affecting the responses to pelleting.On the whole there was no advantage due to pelleting. However, in the absence of bran and antibiotics, and particularly when no animal protein was involved, pigs fed pelleted feed gained faster and had better feed efficiency. Pelleting was found to increase dry matter and energy digestibility when no bran or antibiotics were included in the diet. Conversely, the inclusion of either bran or antibiotics was as effective as pelleting. It is postulated that bran and antibiotics were effective by reason of their effects on the physical nature of the ingesta and on the microbial population of the gastrointestinal tract.