Abstract
Giant leucaena produces high dry matter yields but the foliage contains mimosine, a non-protein amino acid that is toxic to animals, especially non-ruminants. Reducing mimosine concentration in foliage following harvesting may allow for greater use of Giant leucaena and mitigate the negative aspects of higher mimosine concentration in some varieties. We evaluated two methods for post-harvest treatment of foliage of a highly productive interspecific hybrid variety ‘KX2’ for reducing mimosine concentration: (i) maceration treatment; and (ii) extraction with 0.1 N HCl. Mimosine as a percentage of leaf dry matter ranged from less than 1% DM to around 3% DM. Although both methods reduced mimosine concentration, extraction by 0.1 N HCl also reduced gross energy, protein and carbohydrate concentrations of leucaena foliage. The maceration treatment, on the other hand, caused little reduction in crude protein and crude fat concentrations but markedly increased the carbohydrate concentration. ADF and NDF concentrations were also reduced as a result of maceration treatment. The estimated gross energy concentration in macerated foliage was not significantly lower than in unprocessed foliage. A suitable mechanical method for post-harvest maceration of leucaena foliage, e.g. a wood-chipping machine, could be used to reduce mimosine concentration in the foliage, making it safer for feeding to livestock and enhancing the feed value, especially for non-ruminants. These methods should be tested by conducting feeding studies to determine the possible benefits in animal performance from feeding macerated foliage.
Highlights
Giant leucaena (Leucaena leucocephala subsp. glabrata) is a hardy, fast-growing tree legume found in all tropical and subtropical regions of the world
Reducing mimosine concentration in foliage following harvesting may allow for greater use of Giant leucaena and mitigate the negative aspects of higher mimosine concentration in some varieties
In addition to being a high protein producer, Giant leucaena is considered an ideal fodder legume for the tropics for a number of other reasons: (i) it can be grown at high plant density of 20,000 plants/ha (Van den Beldt and Brewbaker 1980); (ii) it grows well in marginal lands, dry areas and eroded slopes; (iii) as a nitrogen-fixing tree legume it fixes high amounts of N (196‒268 kg N/ha) in nodule-forming symbiosis with Rhizobium (Sanginga et al 1989); (iv) because of its deep root system and drought tolerance, it can be grown as a rain-fed fodder without irrigation; and (v) as a perennial fodder, it does not require annual replanting and can be maintained with minimum effort and resources
Summary
Giant leucaena (Leucaena leucocephala subsp. glabrata) is a hardy, fast-growing tree legume found in all tropical and subtropical regions of the world. It is resistant to many diseases and pests and can grow in a wide range of environmental conditions, which include drought, eroded slopes and acidic and alkaline soils (Brewbaker 2008, 2016; Honda et al 2018). It normally grows as a medium-sized tree, Giant leucaena can be maintained as a bushy shrub for use as an animal fodder by repeated harvesting of its foliage during the year (Figure 1) or by pollarding through a cut-and-carry system (Youkhana and Idol 2018). The development of additional leucaena types, which produce fewer or no seeds but are still able to maintain high yielding properties, would be very useful. A number of Giant leucaena interspecific hybrids were developed by Dr James Brewbaker at the University of Hawaii at Manoa (Table 2) (Brewbaker 2008, 2013, 2016; Bageel et al 2020) to improve resistance to the leucaena psyllid insect (Heteropsylla cubana), increase cold tolerance and/or reduce or eliminate seed production, while maintaining high productivity
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