MAINTENANCE OF RUMEN PROTOZOA POPULATIONS IN A DUAL OUTFLOW CONTINUOUS FERMENTER

Using a 2(5-2) fractional factorial design, five factors were screened for their ability to promote rumen protozoa growth in a dual outflow fermenter and on their influence on fermentation. The tested factors w ere the addition of bovine serum (BS, 20 ml litre(-1)) and of a 100 g litre(-1) yeast extract solution (20 mi litre(-1)) to artificial saliv a, the addition of diethystilbestrol (15 mg day(-1)) to fermentation b roths, the reduction of shear stresses by lowering the stirring speed from 260 rpm to 230 rpm, and the improvement of ciliate sequestration by the use of a polyurethane foam belt. In the fermenters, the ciliate population density ranged from 10 mu l(-1) to 58 mu l(-1). The genus Isotricha was rarely observed, with a population density estimated at <0.7 mu l(-1) while Dasytricha was not maintained. All the experimenta l factors markedly influenced total protozoa numbers. Lowering the sti rring speed was the sole beneficial treatment. Nutritional supplements , in particular BS, were all detrimental to Entodinium. Their associat ion was characterised by a significant antagonism. The population size of Polyplastron and Eudiplodinium was lowered only by BS addition, po ssibly through the changes induced in the fermentation pattern.