Maintenance of rumen protozoa populations in a dual outflow continuous fermenter

Abstract

Using a 25–2 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 were the addition of bovine serum (BS, 20 ml litre−1) and of a 100 g litre−1 yeast extract solution (20 ml litre−1) to artificial saliva, the addition of diethystilbestrol (15 mg day−1) to fermentation broths, 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 fermentors, the ciliate population density ranged from 10 μl−1 to 58 μl−1. The genus Isotricha was rarely observed, with a population density estimated at <0·7 μl−1 while Dasytricha was not maintained. All the experimental factors markedly influenced total protozoa numbers. Lowering the stirring speed was the sole beneficial treatment. Nutritional supplements, in particular BS, were all detrimental to Entodinium. Their association was characterised by a significant antagonism. The population size of Polyplastron and Eudiplodinium was lowered only by BS addition, possibly through the changes induced in the fermentation pattern. ©1997 SCI