The evaluation of Leucaena Leucocephala (Lam) De Wit: a renewable protein supplement for low-quality forages

Abstract

The purpose of this study was to evaluate the feed value of Leucaena leucocephala (Lam) De Wit, as a renewable protein supplement for low-quality forages. Eight trials were conducted at the University of Pretoria experimental farm in Hatfield and the Agricultural Research Council experimental farm in Roodeplaat. The overall results showed that Leucaena leucocephala is a suitable protein supplement for low-quality forages.

The chemical composition showed that Leucaena leucocephala forage has adequate potential nutrients. The rate of nitrogen degradation in the shoot was much slower and to a lesser extent than in mature pods with seeds, while the dry matter in the shoot degraded faster and to a greater extent than in the pods. In comparison with other forages (Lucerne, Eragrostis and Veld grass), Leucaena forage experienced a time lag of 6 hours before nitrogen could start degrading unlike the other three forages which did not have time lags. However, the dry matter in Leucaena forage did not experience any time lag, which gave Leucaena forage the best performance among the four forages. Lucerne on the other hand, had more readily available RDP, while Leucaena had more UDP.

The effect of supplementing low-quality forages with varying levels of Leucaena forage was that the combinations between Leucaena and Veld grass gave better performance than the combinations between Leucaena and Eragrostis grass. Crude protein is the limiting factor in the performance of low-quality forages. Therefore, the supplementation of low-quality forage with Leucaena resulted in higher feed intake, digestibility and passage. The addition of Browse PlusTM increased the daily feed intake, the production of rumen ammonia and volatile fatty acids significantly. However, it did not have a significant effect on the rumen environment and the proportions of volatile fatty acids.

The incubation and colour detector methods for the detection of Synergistes jonesii bacteria in the rumens of sheep were found to be simple, reliable and fast. It was confirmed that Synergistes jonesii bacteria can persist for more than four months in the rumens of sheep through autumn and winter drought without Leucaena forage in the diet. It was also shown that seasons have an influence on the level of mimosine in Leucaena forage. Hence, it was recommended that the forage has to be utilised fresh in summer when the level of mimosine is lower to minimise the risk of toxicity.