In addition to the bacteria in the rumen there are many larger (5–250/mm long) organisms which at various times have been designated protozoa Of these the ‘ovals’ (Quin’s and Eadie’s) are now known to be large bacteria (Orpin, 1976) and the ‘flagellates’ Neocallimastix frontalis, Piromonas communis and Sphaeromonas communis are the zoospores of phycomycete fungi (Orpin, 1977a, b) There are genuine flagellates in the rumen, eg Trichomonas spp, Monoceromonas sp and Chilomastix sp, but almost nothing is known about their metabolism (Jensen and Hammon, 1964) The largest, most obvious and most important protozoa are the ciliates, of which there are two groups both in the subclass Trichostomatia The so called ‘holotrich’ protozoa belong to the order Vestibuliferida and the entodiniomorphs to the order Entodiniomorphida, suborder Entodiniomorphina and family Ophryoscolecidae As the properties and metabolism of these two protozoal groups are different, they will be considered separately below

The Rumen Protozoa

Model of cellulose disappearance from the rumen.

The vast increase in the population density of the rumen flagellate Neocallimastix frontalis shortly after the host animal has commenced eating is caused by stimulation of a reproductive body on a vegetative phase of the organism to differentiate and liberate the flagellates. The stimulant is a component of the host's diet. The vegetative stage of N. frontalis bears a strong morphological resemblance to that of certain species of aquatic phycomycete fungi, and consists of a reproductive body borne on a single, much branched rhizoid. The flagellates liberated in vivo within 15 to 45 min of feeding lose their motility within 1 h and develop into the vegetative phase, thus producing a rapid decrease in population density of the flagellates. Conditions for maximum flagellate production are similar to those ocfnring in the rumen: pH 6.5, 39 °C, absence of O2, presence of CO2. Differentiation of the reproductive body is inhibited by compounds affecting membrane structure and function, but not by inhibitors of protein synthesis. The organism was cultured in vitro in an undefined medium in the absence of bacteria or other flagellates.

Studies on the rumen flagellate Neocallimastix frontalis.

1 A procedure for sampling digesta from within the omasal canal of sheep given a variety of roughage diets was used to enable comparison to be made of the composition of effluent from the reticulo-rumen with that of rumen fluid2 Concentrations of protozoa in effluents, relative to a soluble marker continuously infused intraruminally, were usually less than 20% of corresponding rumen fluid concentrations It was estimated that the amount of protozoal nitrogen leaving the rumen represented less than 2% of dietary N3 Passage of volatile fatty acids (VFA) from the rumen in effluent was less than 75% of that indicated by rumen concentrations4 A continuous, in vitro fermentation system was developed, in which outputs of protozoa were comparable with in vivo outputs

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Passage of protozoa and volatile fatty acids from the rumen of the sheep and from a continuous in vitro fermentation system

Anaerobic fungi in herbivorous animals

SUMMARY: The pattern of change of concentration of different groups of microorganisms in the rumen was found to be characteristic of the group and little affected by the time of day, the nature of the diet, or the host animal. The dilution rate of rumen liquor and the rate of change of concentration of several groups of micro-organisms were measured at intervals following feeding; this allowed calculation of the apparent specific growth rate. The changes in concentration of the ophryoscolecid ciliate protozoa, the selenomonads and the oval organism described by Eadie could be explained as the resultant of the changes in dilution rate due to the act of eating and in growth rate in response to incoming nutrients. Rates of change in concentration greater than could be accounted for on the basis of growth and dilution alone were found with the peptostreptococci, the polymastigate flagellate protozoa and the holotrich ciliate protozoa. It is suggested that the peptostreptococci underwent lysis or engulfment by other organisms and that the polymastigates became sequestered, probably close to the rumen wall. The concentration changes of the holotrichs were more difficult to understand, but it would appear that little division took place for some 18 hr after feeding, followed by several divisions in quick succession. The oscillospirae showed two peaks in concentration; no explanation can be offered for this.

Diurnal Changes in the Concentrations of Micro-organisms in the Rumens of Sheep Fed Limited Diets Once Daily: WITH AN APPENDIX ON THE KINETICS OF RUMEN MICROBES AND FLOW

A. C. I. Warner

Papers

Diurnal Changes in the Concentrations of Micro-organisms in the Rumens of Sheep Fed Limited Diets Once Daily: WITH AN APPENDIX ON THE KINETICS OF RUMEN MICROBES AND FLOW