Leucaena rumen inoculum – composition and activity

The Leucaena rumen inoculum – composition and activity project researched the biology and bacterial mix of leucaena rumen inoculum to prevent its degradation at all stages in the supply chain.

Productivity from leucaena-based pasture can be reduced by DHP-induced depressions in intake, DHP being a by-product of ruminal breakdown of mimosine (which occurs at various concentrations in the leucaena plant). This MLA funded project aimed to evaluate, and where necessary improve, the integrity of the supply chain for the DHP-degrading rumen inoculum supplied to cattle grazing leucaena-based pastures.

Leucaena leucocephala (leucaena) is a drought-resistant leguminous fodder shrub/tree that is used as a protein rich forage (up to 34% crude protein (Galindo et al., 1995; Tudsri et al., 2002)) for cattle production.  Before microbial inoculation was practiced, the usefulness of leucaena for cattle production in Australia was limited. While plant enzymes and common rumen bacteria degraded mimosine to 3-hydroxy 4-[1H]-pyridone (3, 4 DHP) they could not degrade it further.  Both mimosine and 3,4 DHP are toxic to cattle and can be absorbed through the rumen wall and, depending on the amount present in the diet, can accumulate in the animal’s system resulting in a clinical condition with symptoms including hair loss, enlarged thyroid and weight loss (Jones, 1979; D’Mello, 1994).  The isolation of Synergistes jonesii, a bacterium that can degrade 3,4 DHP to 2,3 DHP and  2,3 DHP to harmless byproducts, has resulted in the ability to rumen inoculate cattle providing protection against clinical intoxication. Queensland cattle grazing leucaena and inoculated with S. jonesii can achieve liveweight gains of up to 1.5kg/hd/day (Dalzell, 2002). There has been a rapid increase in the area of leucaena under production in Queensland with over 150,000 hectares under production in 2006 and future increases of over 25,000 ha/year expected.

At the time of this research, Queensland’s Department of Agriculture and Fisheries had been providing an inoculum containing S. jonesii to producers for 16 years. Although every batch of inoculum was tested to ensure that it both contained S. jonesii and broke down 3,4 and 2,3 DHP prior to frozen storage, its efficacy had been questioned. The main issues were not with a failure to protect from clinical disease but rather with lower than expected liveweight gains on leucaena/grass grazing systems. A lack of knowledge of the bacterial mix of the inoculum, whether it changed over time, and in particular whether one or more S. jonesii strains were present, was a pivotal issue. In addition, the expression and activity, and how they were regulated, of genes that were involved in the degradation of 3,4 and 2,3 DHP may explain the observation that some herds had high 2,3 DHP levels despite having been inoculated.

To understand the biology of the inoculum and to ensure that it was not being degraded or otherwise losing activity, since its inception, during storage and prior to animal inoculation, the project aimed to define the mixture of bacteria, the strains of S. jonesii and the regulation of genes required for DHP degradation.

To learn more about this research, please read the final report summary and download the final report (B.NBP.0720) (PDF, 1.5MB) from the Meat & Livestock Australia website.

When: 30 May 2012 to 30 November 2015

Contact: Dr Diane Ouwerkerk

Collaborators: Department of Agriculture and Fisheries,   University of Queensland