Evaluation of the productivity and feed value of Wondergraze and Redlands leucaena cultivars under grazing

Context. Leucaena leucocephala (leucaena) is a leguminous shrub used for beef grazing in low-rainfall regions (< 600-700 mm). Newer cultivars have the potential to extend adoption of the species to higher rainfall (> 600-700 mm), frost-free areas of Australia. Aim. We compared productivity, nutritional value and animal performance of two leucaena cultivars, new psyllid-resistant Redlands and the 2010-released Wondergraze, under continuous grazing management in a higher rainfall environment. Methods. Growing steers were allocated to replicated established stands of Wondergraze or Redlands with inter-row mixed grass-legume pasture from January to July 2021. Pasture and leucaena were characterised for biomass and nutritive characteristics. Botanical composition was measured. Liveweight gain, rumen fermentation, and leucaena mimosine breakdown products were measured in grazing steers. Key results. At the beginning of the study, leucaena edible biomass was similar for both cultivars (P > 0.05), but at subsequent samplings, biomass of Redlands was lower than of Wondergraze (P < 0.01). Biomass of both cultivars declined rapidly over the grazing period. Pasture biomass increased between February and July and was significantly higher in Wondergraze paddocks (P < 0.05). Animal performance was not significantly different between cultivar treatments, averaging 0.8 kg/day, but declined over time. Patterns of mimosine conversion to DHP isomers and their conjugation were similar for the two cultivars, suggesting that effectiveness of detoxification did not differ between them. Conclusion. The results demonstrate that leucaena can sustain high levels of animal performance when included in tropical grass pastures in a higher rainfall environment if present in a sufficient quantity (> 2 t leucaena edible dry matter/ha established leucaena).