The leguminous shrub Leucaena leucocephala (leucaena) iswidely used as a forage species for cattle in tropical agriculture. However,leucaena contains the toxic amino acid mimosine. Both mimosine and its primaryruminal degradation product 3-hydroxy-4(1H)-pyridone (DHP) are toxic and theiraccumulation in the animal’s system results in hair loss, reducedliveweight gain, and goitre. The ruminal bacteriumngle cultivar bywithholding water. In Expt 2, plants of EP and MK were grown together in thesame container and received water daily with gradation in intensity of waterdeficit achieved by varying the daily water ration per container.All cultivars in each experiment exhibited commonly reported responses towater deficit, characterised by diminished evaporative surface area andincreased root : shoot ratio. The response of MK was primarily morphologicaland MK plants had smaller plant size, higher root : shoot ratio,

Abstract. Methane emissions from ruminant livestock represent a loss of carbon during feed conversion, which has implications for both animal productivity and the environment because this gas is considered to be one of the more potent forms of greenhouses gases contributing to global warming. Many strategies to reduce emissions are targeting the methanogens that inhabit the rumen, but such an approach can only be successful if it targets all the major groups of ruminant methanogens. Therefore, a thorough knowledge of the diversity of these microbes in different breeds of cattle and sheep, as well as in response to different diets, is required. A study was undertaken using the molecular techniques denaturing gradient gel electrophoresis, DNA cloning and DNA sequence analysis to define the extent of diversity among methanogens in ruminants, particularly Bos indicus cross cattle, on differing forages in Queensland. It was found that the diversity of methanogens in forage-fed cattle in Queensland was greater than in grain-fed cattle but there was little variability in methanogen community composition between cattle fed different forages. The species that dominate the rumen microbial communities of B. indicus cross cattle are from the genus Methanobrevibacter, although rumen-fluid inoculated digestors fed Leucaena leucocephala leaf were populated with Methanosphaera-like strains, with the Methanobrevibacter-like strains displaced. If ruminant methane emissions are to be reduced, then antimethanogen bioactives that target both broad groups of ruminant methanogens are most likely to be needed, and as a part of an integrated suite of approaches that redirect rumen fermentation towards other more useful end products.

Aim: To isolate bacterial viruses that infect the ruminal cellulolytic bacterium Ruminococcus albus. Methods: Four phages infecting R. albus AR67 were isolated under anaerobic conditions using the soft-agar overlay technique. The phages were characterized on morphology, solvent stability, nucleic acid type and digestion characteristics. Two phages, /Ra02 and /Ra04 comprised icosahedral virions with linear double-stranded DNA and appeared to belong to the family Tectiviridae. The other two phages are most likely filamentous phages with circular single-stranded DNA of the family Inoviridae. Significance of the Study: Viruses of the families Tectiviridae and Inoviridae have not previously been isolated from rumen bacteria. The phages isolated in this study are the first phages shown to infect the cellulolytic bacteria of the rumen. This suggests that the cellulolytic populations of the rumen are subject to lytic events that may impact on the ability of these bacteria to degrade plant fibre and on the nutrition of the animal.

Rumen microbial populations were measured in Brahman-cross steers that were relocated from spear grass (Heteropogon contortus) dominant pastures in northern Queensland to buffel grass (Cenchrus ciliasis) dominant pastures in central Queensland, to assess whether aspects of rumen function may contribute to the sometimes reported depressed growth rates following relocation. Nine genera of ciliate protozoa (Isotricha, Dasytricha, Entodinia, Epidinium, Diplodinium, Ostracodinium, Metadinium, 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 study was conducted. Protozoal population composition fluctuated only slightly over the sampling period. Entodinia were predominant, occupying 50-70% of the population. Population density varied according to season, with the highest density (4-8×105 /mL rumen fluid) occurring in the wet season. Bacterial and protozoal populations were remarkably stable and little affected by relocation. Again, the major impact on population density was the season, with all carbohydrate (soluble sugar, starch, xylan, and cellulose) utilising bacterial subpopulations reaching the greatest density with the onset of the wet season.