In vitro digestibility, crude protein, and mineral concentrations of Leucaena leucocephala accessions in a wet/dry tropical region of Venezuela

An experiment was conducted on a commercial farm located in the western part of Venezuela (10.5 degrees N and 72 degrees W; mean annual rainfall of 1000 mm; mean annual temperature of 28 degrees C; sandy-loam Alfisol with pH of 5.5). The purpose of the experiment was to evaluate the in vitro organic matter digestibility (IVOMD), crude protein (CP) content and mineral composition of four Leucaena leucocephala (Lam.) De Wit accessions under rotational grazing by heifers over a 6-month period covering dry and rainy seasons, using a split-plot experimental design with two replications. Neither accessions nor the accession X season interaction affected (P>0.05) any of the variables. The mean IVOMD was 68.6%, whereas CP content during the rainy season (26.5%) was higher (P<0.05) than in the dry season (24.3%). Average mineral content of the accessions were adequate in relation to grazing ruminant requirements with the exception of phosphorus [(P) 0.13%], sodium [(Na) 0.038%], copper [(Cu) 6.9 ppm], and zinc [(Zn) 19.7 ppm]. Forage P concentration may have been influenced by the low soil P content of the experimental site. The mean forage Ca:P ratio (11.3:1) was considerably wider than desirable. During the dry season, ash content increased (P<0.05), Na, iron (Fe), and cobalt (Co) decreased (P<0.05), but Fe and Co still remained above the critical levels. Mean concentrations of other elements were not affected (P>0.05) by season. Forage molybdenum (Mo) concentrations were low and, therefore, would not result in conditioned Cu deficiency. The four L. leucocephala accessions had similar feeding value for grazing ruminants and their quality was not markedly reduced in the dry season. Mineral supplementation of ruminants grazing this legume may be needed to correct specific deficiencies and imbalances.