Studies on the Composition of the Ruminal Flora and Fauna of Young Calves

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Summary A study was made of the bacteria and protozoa present in the rumen of three calves from 1 to 13 wk. of age, raised under normal conditions. Ciliate protozoa were not established in these calves. A study of older calves in contact with mature animals after 13 wk. of age indicated that entodinia were first established, followed by diplodinia and holotrichs. Total anaerobic bacterial counts were somewhat higher for the calves than for mature animals. Counts of cellulolytic bacteria were similar to those of a mature animal when calves were 3 wk. old and were quite high even at 1 wk. Lactate-fermenting bacteria were present in high numbers at from 1 to 3 wk. of age, but declined to numbers similar to those of the adult at 9 to 13 wk. Bacteria capable of growth under aerobic conditions and coliforms were highest in numbers when calves were 1 and 3 wk. of age. Even at 13 wk. these counts were higher than those of the adult. Detailed studies of strains of predominant bacteria revealed 21 different groups that could be grouped on the basis of their occurrence in animals of different ages. The predominant bacteria found in 1- to 3-wk.-old calves were mainly different from those of mature cattle. When calves were 6 wk. of age many groups of bacteria typical of mature animals were found, but several groups not found in mature animals remained. At 9 and 13 wk. of age, bacteria isolated were mainly those typical of mature animals. That the rumen is physiologically well-adapted for the development of its flora at a very early age is suggested by the following similarities between week-old calves and adults. Most bacteria were nonspore-forming strict anaerobes and higher counts were obtained in rumen fluid agar than in a trypticase-soy agar. Some predominant groups of bacteria were similar, and cellulolytic counts were relatively high in calves, even though milk and straw bedding were the only foods available.