RUMEN BACTERIAL AND PROTOZOAL POPULATIONS IN CATTLE BEING RELOCATED IN TROPICAL QUEENSLAND

Rumen microbial populations were measured in Brahman-cross steers that were relocated from spear grass (Heteropogon contortus) dominant past ures in northern Queensland to buffel grass (Cenchrus ciliasis) domina nt pastures in central Queensland, to assess whether aspects of rumen function may contribute to the sometimes reported depressed growth rat es following relocation. Nine genera of ciliate protozoa (Isotricha, D asytricha, Entodinia, Epidinium, Diplodinium, Ostracodinium, Metadiniu m, Elytroplastron, and Eudiplodinium) were recorded in the rumen fluid of the steers. In most steers all genera were present at any time and the generic mix persisted throughout the 10 months over which the stu dy was conducted. Protozoal population composition fluctuated only sli ghtly over the sampling period. Entodinia were predominant, occupying 50-70% of the population. Population density varied according to seaso n, with the highest density (4-8x10(5)/mL rumen fluid) occurring in th e wet season. Bacterial and protozoal populations were remarkably stab le and little affected by relocation. Again, the major impact on popul ation density was the season, with all carbohydrate (soluble sugar, st arch, xylan, and cellulose) utilising bacterial subpopulations reachin g the greatest density with the onset of the wet season.