Effect of Antibiotics on Growth and Nutrient Absorption of Chicks

IN A recent study from this laboratory, on the mode of action of antibiotics as growth stimulants for young animals, a transitory period of growth depression was observed around the 8th day of life in chicks fed an antibiotic-free, casein-sucrose diet (Eyssen and De Somer, 1963). The inhibition of weight gain was found to be associated with decreased efficiency of feed utilization and malabsorption of fats and carbohydrates, and the syndrome was most pronounced when sucrose was fed as the sole source of dietary carbohydrate. Addition to the feed of 20 p.p.m. of virginiamycin, an antibiotic active only against Gram-positive microorganisms, resulted in improved intestinal absorption and stimulated growth. As a result of these studies, the hypothesis was proposed that the growth-stimulating effect of antibiotics is most likely due to suppression of intestinal Gram-positive microorganisms which interfere with the absorption of nutrients. The present investigations were performed to obtain…