The nutritive value of Rhodes grass (Chloris gayana) when treated with CaO, NaOH or a microbial inoculant and offered to dairy heifers as big-bale silage

A series of laboratory and animal studies examined the use of chemical and biological agents to enhance the digestibility of Rhodes grass (grass) cut at 60 (young) and 100 (mature) days of regrowth and ensiled as big round bales. The treatments included an untreated control (C), a microbial inoculant (I), NaOH, CaO and NaOH plus inoculant (NaOH + I). Inoculant was grown anaerobically, using a starter culture of rumen fluid from cattle given Rhodes grass. Treatments C, I, NaOH, NaOH + I, were offered separately to twelve dairy heifers, in a 3 ✕ 4 randomized complete block design, repeated twice for each grass silage. C and I had substantial mould growth, compared with no visible mould in NaOH or NaOH + I. CaO treatment was effective in preventing mould growth, but had little effect on the chemical composition and in sacco digestibility of mature grass silage. NaOH reduced NDF content and increased in sacco digestibility (P < 0·05) but not the in vivo digestibility (P > 0·05) of both mature- and young-grass silage. The effects of other treatments on nutritive value were non-significant at both stages of maturity. NaOH increased the intake of mature-grass silage by 24-26% (P < 0·05), but had little effect on the intake of young-grass silage (P > 0·05). Treatment I consistently reduced grass silage intake (P < 0·05) for young-grass silage. The findings of these studies show that treating mature Rhodes grass with NaOH will improve its nutritive value and reduce mould growth in conserved herbage. However none of the treatments in this study had any consistently positive effects on the in vivo nutritive value or storage quality of young-grass silage.

Persistence of orally administered Megasphaera elsdenii and Ruminococcus bromii in the rumen of beef cattle fed a high grain (barley) diet

When cattle are fed grain, acidotic ruminal conditions and decreased efficiency in starch utilisation can result from the rapid production and accumulation of lactic acid in the rumen. The efficacy of drenching cattle with Megasphaera elsdenii and Ruminococcus bromii to improve animal performance was investigated. A feedlot trial was undertaken with 80 Bos indicus crossbred steers (initial liveweight 347.1 (s.d. 31.7) kg) in 10 pens in a randomised complete block design. An empty-pen-buffer was maintained between treated (inoculated) and untreated (control) groups to avoid transfer of inoculant bacteria to the control steers. Inoculated steers were orally drenched with M. elsdenii YE34 and R. bromii YE282, and populations increased rapidly over 3–14 days. The steers were fed for a total of 70 days with commercial, barley-based, feedlot rations. High growth rates (1.91 kg per day) were achieved throughout the experiment in both the inoculated and control steers. Intakes averaged 21.3 g dry matter (DM) per kg liveweight per day. There was probably no acidosis achieved in this trial following challenge (i.e. no change in pH occurred). There were no differences in any production or carcass measurements between the control and inoculated steers overall. However, the control group acquired dense ruminal populations of M. elsdenii by Day 14, while R. bromii populations established at high densities within the first 2 weeks but then declined and were undetectable by Day 50. R. bromii appears to be only transiently dominant, and once its dominance waned, it appeared that Ruminobacter spp. established in the rumen. Ruminobacter spp. became dominant between 14 and 28 days in all the steers examined and persisted through to the end of the study. These Ruminobacter spp. may be of future interest in the development of probiotics for grain-fed cattle.

Adaptation behaviour of local and rangeland cattle relocated to a temperate agricultural pasture

Relocating cattle from rangeland properties to agricultural pastures in southern Western Australia allows producers to improve year-round continuity of feed supply in their beef cattle businesses, and can reduce substantially the time taken to grow animals to meet market specifications. In this study the behaviour and growth of two groups of young cattle that were sourced from different locations was evaluated after they were transferred to a new extensive grazing system. In Experiment 1, 122 Limousin-cross heifers that were raised in the agricultural region of Western Australia (AR cattle) were transferred to the experimental site from a neighbouring property (~10 km away). In Experiment 2, 95 Brahman-cross heifers that were raised in the rangelands of Western Australia (RR cattle) were transferred to the experimental site. Animal growth and behaviour were analysed across time and differences in the time-course of behavioural changes between the groups were compared. Rate of liveweight gain in the AR cattle remained consistent (~1.2 kg/day) during the experiment. There was an increase in horizontal (16%; P < 0.001) and vertical (12%; P = 0.002) head movement in AR cattle over the first several weeks after relocation, indicative of increased grazing activity, but there was little change in other behaviours over the duration of the experiment. In contrast, the RR cattle had reduced growth during the first 4 weeks after relocation (P < 0.001). From weeks 2–4 weight gain in RR cattle was 0.31 kg/day, approximately one-quarter of their average daily gain attained 4 weeks later. During the first 6 weeks, RR cattle showed behavioural changes indicative of adaptation, including a 61% increase in horizontal head movements, suggesting more grazing activity. The paddock area utilised daily by RR cattle was 32% higher in week 6 compared with week 1, and during daylight hours (0600–1900 hours) they began to travel more (23%) and spent more time active (16%). We conclude that rangeland-raised Bos indicus heifers take from 4 to 6 weeks to adapt from their previous large paddocks/natural plant environment to a new temperate agricultural environment. Our results suggest that the cause of lost productivity in rangeland cattle when they are relocated to a temperate pasture is at least in part due to initial lower grazing activity as they become familiar with the new environment.

Hydrogen utilising bacteria from the forestomach of eastern grey (Macropus giganteus) and red (Macropus rufus) kangaroos

Reductive acetogenesis is an alternative to methanogenesis for removing hydrogen produced during enteric fermentation. In Australia, kangaroos have evolved an enlarged forestomach analogous to the rumen of sheep and cattle. However, unlike sheep and cattle, kangaroos produce very little methane from enteric fermentation. From samples of gut contents from five eastern grey and three red kangaroos, we were not able to detect methanogens using a PCR protocol, but did detect the formyltetrahydrofolate synthetase (FTHFS) gene (likely to be used for reductive acetogenesis) in all animals. Isolations to recover acetogens resulted in two different classes of hydrogen consuming bacteria being isolated. The first class consisted of acetogens that possessed the FTHFS gene, which except for Clostridium glycolicum, were not closely related to any previously cultured bacteria. The second class were not acetogens but consisted of enterobacteria (Escherichia coli and Shigella) that did not possess FTHFS genes but did utilise hydrogen and produce acetate. Enumeration of the acetogens containing the FTHFS gene by real-time PCR indicated that bacteria of the taxa designated YE257 were common to all the kangaroos whereas YE266/YE273 were only detected in eastern grey kangaroos. When present, both species occurred at densities above ×106 cell equivalents per mL. C. glycolicum was not detected in the kangaroos and, unlike YE257 and YE266/273, is unlikely to play a major role in reductive acetogenesis in the foregut of kangaroos.

Diversity of methanogens in ruminants in Queensland

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.

Characterization of culturable anaerobic bacteria from the forestomach of an eastern grey kangaroo, Macropus giganteus

AIM

To determine the culturable biodiversity of anaerobic bacteria isolated from the forestomach contents of an eastern grey kangaroo, Macropus giganteus, using phenotypic characterization and 16S rDNA sequence analysis.

METHODS AND RESULTS

Bacteria from forestomach contents of an eastern grey kangaroo were isolated using anaerobic media containing milled curly Mitchell grass (Astrebla lappacea). DNA was extracted and the 16S rDNA sequenced for phylogenetic analysis. Forty bacterial isolates were obtained and placed in 17 groups based on phenotypic characteristics and restriction enzyme digestion of 16S rDNA PCR products. DNA sequencing revealed that the 17 groups comprised five known species (Clostridium butyricum, Streptococcus bovis, Clostridium sporogenes, Clostridium paraputrificum and Enterococcus avium) and 12 groups apparently representing new species, all within the phylum Firmicutes.

CONCLUSIONS

Foregut contents from Australian macropod marsupials contain a microbial ecosystem with a novel bacterial biodiversity comprising a high percentage of previously unrecognized species.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study adds to knowledge of Australia's unique biodiversity, which may provide a future bioresource of genetic information and bacterial species of benefit to agriculture.

A lack of predatory interaction between rumen ciliate protozoa and Shiga-toxin producing Escherichia coli

AIMS

To investigate interactions between rumen protozoa and Shiga toxin-producing Escherichia coli (STEC) and to ascertain whether it is likely that rumen protozoa act as ruminant hosts for STEC.

METHODS AND RESULTS

The presence of stx genes in different microbial fractions recovered from cattle and sheep rumen contents and faeces was examined using PCR. In animals shedding faecal STEC, stx genes were not detected in the rumen bacterial or rumen protozoal fractions. Direct interactions between ruminal protozoa and STEC were investigated by in vitro co-incubation. Rumen protozoa did not appear to ingest STEC, a STEC lysogen or non-STEC E. coli populations when co-incubated.

CONCLUSIONS

The ruminal environment is unlikely to be a preferred habitat for STEC. Bacterial grazing by rumen protozoa appears to have little, if any, effect on STEC populations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicates that ruminal protozoa are unlikely to be a major factor in the survival of STEC in ruminants. They appear as neither a host that protects STEC from the ruminal environment nor a predator that might reduce STEC numbers.

Genetic homogeneity and phage susceptibility of ruminal strains of Streptococcus bovis isolated in Australia

The genetic homogeneity of 37 strains of ruminal streptococci was investigated by comparing DNA fragment profiles on agarose gels following restriction endonuclease digestion with Hae III, Cfo I and Msp I. Thirty strains were indistinguishable from Streptococcus bovis strains, 2B, H24 and AR3. The remaining three strains were similar but not identical to a ruminal strain of Strep. intermedius (AR36). In addition, the susceptibility of these strains to infection by five bacteriophages was examined. Three of the phages (phi Sb02, phi Sb03 and phi Sb04) were specific to the strain of Strep. bovis from which they were isolated, while phages 2BV and phi Sb01 infected one and two strains, respectively, in addition to their primary host. It was concluded that although Strep. bovis is relatively homogeneous genetically, broad host range phages appear to be uncommon with this bacterial species.