Possible causes of the high death rate of ciliate protozoa in the rumen

SUMMARYThe protozoa in washed suspensions of rumen ciliates were killed by freezing or heating at 49 °C for 5 min before incubation at 39 °C, aeration during incubation or incubation in hypotonic salt solution (30% of ncrmal) and released their intracellular cellulose and amylase during 4–6 h. With the last two treatments it was only necessary to expose the protozoa to the conditions for 2 min to obtain over 50% of maximal enzyme release 4–6 h later. It is suggested that death of the protozoa during exposure to air and/or hypotonic salt solution for short times during drinking and rumination by the host animal could be the explanation for the high postulated protozoal death rate in the rumen. The amylase and cellulase released from the protozoa tested were stable in the presence of mixed rumen bacteria for 1·5 h and could be of importance in the degradation of plant constituents in the rumen.