B.GBP.0026 - QDAF Final Report - leucaena inoculum

Summary

Leucaena leucocephala, a perennial browse legume, represents one of the few nutritional options to significantly improve beef productivity in northern Australia. This project used expert knowledge and existing spatial data sets to map potential distribution in Queensland, the Northern Territory, and northern Western Australia, estimating that up to 27.3M hectares of land in Northern Australia could viably support Leucaena-grass pasture grazing systems. This included 4.6M hectares in humid coastal areas of Queensland that are suitable for the psyllid-resistant Redlands cultivar, with economic analysis of further adoption suggesting a total benefit of $61–123M over the next 40 years across northern Australia.

To maximise the benefits for cattle grazing Leucaena, the cattle need rumen bacteria capable of degrading the toxins mimosine, 3,4 DHP and 2,3 DHP. This project investigated the effect of the Redlands cultivar on the current DAF inoculum resulting in the development of a new mixed bacterial inoculum (TriMix), adapted for better utilisation of the three different Leucaena cultivars, Redlands, Wondergraze and Cunningham. An on-property survey of the presence of de-toxifying bacteria in the rumen found that cattle which had never been exposed to Leucaena did not possess rumen bacteria able to degrade the toxins 3,4 DHP and 2,3 DHP so would benefit from receiving the Department of Agriculture and Fisheries Leucaena inoculum if being moved to a Leucaena-grass pasture grazing system.

Objectives

The aims of this project were met through the following two objectives:
1. Determine the efficacy of the current and modified Leucaena inoculum for cattle grazing the new psyllid resistant and future sterile cultivars.
2. Establish the range and extent of land that is suitable for the growth of Leucaena cultivars.

Key findings

The key findings of the project were:
- The psyllid resistant Redlands Leucaena cultivar was found to negatively impact the DAF Leucaena inoculum’s ability to degrade two of the toxins, 3,4 DHP and 2,3 DHP, within initial in vitro fermentations. To address this loss of activity, a TriMix Leucaena inoculum has been developed containing bacterial populations adapted to effectively ferment and detoxify, plant material from all three different Leucaena cultivars (Cunningham, Redlands and Wondergraze).

- The on-property survey results have shown that populations of rumen bacteria able to completely degrade the toxic compounds in Leucaena, are not naturally present in Australian cattle. The rumen bacterial populations in cattle that have never been exposed to Leucaena were unable to degrade the toxins 3,4 DHP or 2,3 DHP. Use of the DAF inoculum to introduce the toxin-degrading bacteria to naïve cattle, is recommended to ensure the maximum benefit from utilising Leucaena-pasture grazing. The survey showed that these bacteria can be maintained by management practices to ensure its spread to new animals being introduced to Leucaena-pasture grazing.

- Mapping estimated up to 27.3M hectares of land in northern Australia could viably support Leucaena-grass pasture grazing systems. This includes 4.6M hectares in humid coastal areas of Queensland that are suitable for the Redlands cultivar, and where other cultivars have previously been non-viable due to predation from psyllids. The economic analysis suggests a total benefit of $61–123M over the next 40 years across northern Australia. More than 90% of this will be generated in Queensland including $13–26M from cv Redlands cultivation.

Benefits to industry

The benefits for the industry will be:

• the production of the DAF TriMix inoculum, a new mixed bacterial rumen inoculum capable of degrading 3,4 DHP and 2,3 DHP efficiently and effectively, when used in animals grazing different Leucaena cultivars, including the psyllid resistant Redlands
• scientific evidence provided by an on-farm survey, on which management practices enable cattle to possess the rumen bacteria able to completely degrade the toxic compounds associated with feeding Leucaena
• the identification and mapping of land areas in Northern Australia which could viably support Leucaena-grass pasture grazing systems available to enable future expansion
• estimated economic benefits of future expansions to the industry modelled over the next 40 years.

MLA action

Further research into Leucaena should focus on sterile varieties, novel technology for expansion and WA demonstration sites.

Future research

The work on the efficacy of the current DAF Leucaena inoculum resulted in an improved mixed bacterial rumen TriMix inoculum providing bacterial populations adapted to three cultivars which quickly established detoxifying populations in fermentations. The recommendation from this project is for production of the DAF Leucaena inoculum to shift to the TriMix from the next production run.

Future research into the bacteria present in the rumen capable of degrading 3,4 DHP and 2,3 DHP will include rumen microbiome sequencing of the 72 animals sampled within the on-property survey and metagenome sequencing of rumen fluid from selected animals. Results and recommendations to industry from on-property survey will be communicated to industry through future planned communication activities including an article in the FutureBeef Newsletter and a FutureBeef or Leucaena Network webinar.

This project established the range and extent of land that is suitable for the growth of Leucaena cultivars and indicates broader areas of northern Australia where industry can scale up planning with agronomic and economic advisors, for best results. This planning could focus on optimal placement of Leucaena at property scale, appropriate weed Leucaena control, and more targeted analysis of potential financial outcomes.

This project suggests the broader areas that would be useful starting points for finer scaled planning involving agronomic and economic advisors. Future projects with extension-based activities focusing on the optimal placement of Leucaena at property scale, appropriate weed control and more targeted analysis of potential financial outcomes to demonstrate the benefits of Leucaena for Northern Australian producers should be undertaken.