THE EFFECT OF CHLORTETRACYCLIN E FEEDING ON IN VITRO CELLULOSE DIGESTION BY

HE growth-stimulating effect of chlortetracycline (Aureomycin) feeding to dairy calves has been demonstrated by many investigators but the effects on older cattle are not so extensive and are less con- clusive. Neumann et al. (1951) found no beneficial effects when chlor- tetracycline was added to a basal fattening ration, whereas Perry et al. (1954) found chlortetracycline-fed steers gained faster than control animals. B artley and associates (1953) and Rusoff et al. (1952) reported chlortetracycline feeding had no apparent effect on milk production. Bell et al. (1951) found chlortetracycline feeding to two steers decreased the apparent digestibility of crude fiber, which suggested depressed activity of cellulolytic microorganisms. Hungate et al. (1955) in mano- metric experiments demonstrated that chlortetracycline feeding altered the composition of the rumen microbial population. Methane production was diminished, probably due to inhibition of the production of inter- mediates. Lodge (1954) found that inoculums from chlortetracycline- fed cows consistently digested a lower percentage of purified cellulose than did those from control cows. Furthermore, when chlortetracycline was removed from the diet of two calves (Lodge, 1954), the in vitro cellulose digestion, which previously had been depressed, increased to apparently normal values. Inasmuch as further study of the effects of this antibiotic on cellulolytic microorganisms seemed desirable, the present investigation was undertaken to determine the effect of chlor- tetracycline feeding on the in vitro digestion by rumen microorganisms of (a) purified cellulose and (b) cellulose in a natural feed (alfalfa hay).