The Effect of Starvation and Subsequent Refeeding on some Activities of Rumen Microorganisms In Vitro

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Abstract
Samples of rumen fluid were collected at intervals from a fistulated steer fed (1) a high-roughage ration regularly, (2) no ration, starvation for 3 days, (3) refed (following starvation) a high-roughage ration. The abilities of rumen fluid to digest cellulose in vitro and to reduce the viscosity of a stable suspension of carboxymethylcellulose (CMC) were determined. A fraction (S-1) of rumen fluid freed of protozoa and most plant material and a second fraction (S-2) freed of bacteria, protozoa and plant material were also tested for activity on CMC. The pH of rumen fluid rose continuously during the starvation period to a high between 7.65 and 7.94. The ability of rumen fluid to digest cellulose in vitro decreased greatly when the steer was starved for 3 days. All fractions of rumen fluid also decreased in their activity on CMC. Fractions of rumen fluid obtained shortly after feeding had been resumed following starvation showed unusually high, but approximately equal, activity on CMC. The extremely high activities of the S-2 fractions indicated that the enzymes were largely extracellular at that time. The ability to digest cellulose in vitro was normal in 3 to 4 days after feeding was resumed following starvation. Activities of the various fractions on CMC were normal when the steer had been refed 2 to 4 days after starvation with one exception. This exception might have been the result of a change in the normal proportion and metabolism of microbial life in the rumen. No differences in the activities of rumen microorganisms could be attributed to the type of hay the steer received before or after the starvation period. The steer readily consumed all of its ration at each feeding. Copyright © . .