Abstract
Leucaena leucocephala (leucaena) is a valuable forage tree legume for tropical animal production, which contains the toxin mimosine. The breakdown products of mimosine in ruminants (3,4-DHP and 2,3-DHP) can adversely affect their health and limit weight gains (Jones and Hegarty 1984). The rumen bacterium Synergistes jonesii, introduced into Australia in 1983, was shown to completely and rapidly degrade these toxins to safe levels (Jones and Megarrity 1986). Since 1996, an inoculum has been produced in vitro and made commercially available to Australian graziers (Klieve et al. 2002). Accordingly, the issue of leucaena toxicity in Australia was thought to be resolved. However, extensive testing in 2004 found that up to 50% of Queensland cattle herds consuming leucaena were excreting high levels of urinary DHP, suggesting subclinical toxicity remained an issue for graziers (Dalzell et al. 2012). Some of these herds had previously been inoculated with in vitro S. jonesii, suggesting the inoculum may not be able to either persist within a herd, or remain effective in degrading DHP. The aim of this study was to assess the capability of the in vitro S. jonesii inoculum to efficiently break down DHP in a controlled feeding trial environment.
Highlights
Leucaena leucocephala is a valuable forage tree legume for tropical animal production, which contains the toxin mimosine
Concentrations of DHP were measured by HPLC (Graham et al 2013), and urine volume was recorded, allowing total DHP excreted to be expressed in mg/hd/d
Total DHP had peaked at 3 weeks and was already declining at 6 weeks, when animals were first inoculated (Figure 2). This was associated with a decline in the isomer 3,4-DHP, while the isomer 2,3-DHP, which first appeared at week 2, remained static until after inoculation
Summary
Leucaena leucocephala (leucaena) is a valuable forage tree legume for tropical animal production, which contains the toxin mimosine. The rumen bacterium Synergistes jonesii, introduced into Australia in 1983, was shown to completely and rapidly degrade these toxins to safe levels (Jones and Megarrity 1986). Extensive testing in 2004 found that up to 50% of Queensland cattle herds consuming leucaena were excreting high levels of urinary DHP, suggesting subclinical toxicity remained an issue for graziers (Dalzell et al 2012). Some of these herds had previously been inoculated with in vitro S. jonesii, suggesting the inoculum may not be able to either persist within a herd, or remain effective in degrading DHP
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