The Effect of Antibiotics on the Intestine of the Chick

During work on the effect of penicillin on vitamin A metabolism in the chick (Coates, Harrison, Kon, Porter & Thompson, 1952) it was observed that the small intestines of birds given penicillin in the diet appeared thinner than those of their controls.A further investigation was therefore undertaken to study the importance of this phenomenon in the mechanism of antibiotic growth promotion.The experiments were of two types, the first dealing with the quantitative and qualitative changes in the gut and the second with the possible mode of action of penicillin in reducing gut weight.They have accordingly been presented here in two separate sections. EXPERIMENTAL AND RESULTS General methodsManagement of the birds.Day-old sex-linked Rhode Island Red x Light Sussex cockerels were used in most of the experiments but occasionally pullets were included.Brown Leghorn x Barred Rock sex-linked pullets and cockerels were used in a few experiments.T h e birds were housed either in Hearson electrically heated brooders (Coates, Kon & Shepheard, 1950) or in small-animal cages inside isolation units (Coates, 1953).Experimental groups consisted of up to thirty-six birds and were sometimes distributed between two or three brooder compartments.Diets.The basal diet was the chick mash normally used in this laboratory, which supports excellent growth up to 4 weeks of age.It had the following percentage composition: maize 35, wheat 30, miller's offals 8.5, fish meal 10, dried skim milk 7.5, dried grass 3, dried brewer's yeast 3, limestone 1.5, salt mixture* 0.5, arachis oil (containing 64 i.u.vitamin D and 680 i.u.vitamin A/g) I .This basal diet was supplemented with antibiotics or other substances according to the experimental requirements.The amounts added were as follows: Procaine penicillin 45-5 mg/kg diet Chloramphenicol 25 mg/kg diet Arsanilic acid 20 mg/kg diet Raw beef liver 30 g/kg dietMeasurements of the gut.The chicks were killed in the customary way by breaking the neck.T h e abdomen was opened, and the gut was removed, slit longitudinally and washed in a beaker of water to remove food particles.It was then blotted lightly