The present investigation is concerned with the influence of procaine penicillin and aureomycin on digestion. In particular, the effect of antibiotics, in amounts generally included in feeding-stuffs, on the bacterial digestion of cellulose in the large intestine of the pig, was investigated.

The digestibility of a basal diet composed of fine bran, maize meal, dried lucerne meal and whitefish meal was determined with and without the addition of antibiotic. No effect was noted on the digestibility of any food constituent.

The diet fed in four digestion trials contained 500 g. of shredded fodder cellulose. The digestion coefficient for the crude fibre, in these diets rich in cellulose, was 76·2% when 18 mg. of procaine penicillin was added per lb. of meal and 76·8% when no antibiotic was added.

The nitrogen-free extractives in the fodder cellulose are mainly if not entirely composed of xylan. If the nitrogen-free extractives and crude fibre are combined to give ‘cellulose’ as defined by Norman & Jenkins, the digestion coefficients for the cellulose were 85·7, 83·4, 85·7 and 87·2%, respectively, thus showing little difference between treatments.

There is no warrant for assuming that the antibiotics had any bactericidal or bacteriostatic effect on the cellulose-splitting organisms.