Four gnotobiotic lambs were fed, after weaning, on a pelleted concentrate diet containing 90% barley. They were inoculated with a defined flora of 11 species of bacteria designed to reproduce the feed digestion of the conventional lamb. Cultural assessments of the growth of the bacteria and analysis of rumen fermentation products showed that rumen function was near normal, and the lambs grew steadily. However, at an age of about 115 to 130 d, rumen function seemed to fail in three of the lambs and they rapidly lost weight and died. The fourth lamb was removed from isolation at about the same time, when there was some slight indication of loss of rumen function. Kept among conventional lambs it then continued to gain weight as did the conventional animals, but its rumen flora changed. The main species in the defined flora remained as major components of the rumen population after the lamb had been exposed to other animals, but in addition a mixed population of other bacteria, like that in conventional animals, quickly developed.

Other experiments showed that gnotobiotic lambs could be routinely weaned on to a concentrate feed containing 45% barley and 50% grass and that, when the lambs were inoculated with a defined flora similar to that given to the lambs in the first experiment, an adequate rumen fermentation could be established and the animals would grow. On changing to an all-grass feed, however, rumen function declined and the lambs ceased to grow. A change back to the barley/grass diet restored rumen fermentation and lamb growth, but whereas amylolytic bacteria were present in normal numbers, cellulolytic bacteria were absent and there appeared to be little, if any, fibre digestion. However, the rumen function again appeared to fail at about the same age of lamb as in the first experiment.


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