Forage yield and compositional analysis of Leucaena species and hybrids adapted to cool sites

Four species of Leucaena (L. leucocephala, L. diversifolia 2n and 4n, andL. pallida) and three interspecific hybrids KX1 (L. diversifolia × L. pallida), KX2 (L. leucocephala × L. pallida), and KX3 (L. leucocephala × L. pallida) were evaluated for forage yield on a cool upland site at the Mealani Research Station on the island of Hawaii (900 m elevation). Two-month-old seedlings were planted at a density equivalent to 40,000 trees/ha and coppiced (harvested) every six months for a two-year period. Leaf material collected from the plots was oven-dried, finely ground, and evaluated for forage components and digestibility.Two Holstein steers fitted with cannulae in the rumen and proximal duodenum were used to conduct a replicated trial to examine rumen and post-rumen dry matter and crude protein digestibility of leaf material. Nylon bags containing leaf material from K636 (L. leucocephala), KX2 (L. leucocephala × L. pallida), or K376 (L. pallida) were suspended in the rumen for periods of 0, 4, 8, 12, 24, 36, and 48 hours. Weight loss was measured and nitrogen content of each sample was determined using a macro-Kjeldahl procedure. Subsequently, rumen-incubated material was placed in nylon bags, inserted into the duodenal cannulae of the two steers and collected in the feces for periods of 24 h after insertion.Results indicate that varieties and hybrids of Leucaena are adapted to cool sites and produce good yields of high quality forage. No significant difference was found in either ruminal or intestinal dry matter or crude protein disappearance between K636 and KX2 whereas K376 was significantly lower for both values. Nearly 40% of dietary crude protein in the K636 and KX2 leaf material escaped ruminal digestion whereas nearly 70% was non-digested for K376. For K636 and KX2, intestinal availability of that protein which escaped ruminal digestion was nearly 50% whereas only 20% of ruminal escape protein of K376 was available in the intestines. Because KX2 produced higher forage yields, plantings on cool sites would favor the use of KX2 over K636 if animal acceptability and rumen retention of dry matter are not problems.