The discriminatory potential of n-alkanes in tropical grasses (Brachiaria brizantha Stapf. cv. Marandu, Cynodon dactylon Pers. cv. Coast-cross 1 and Panicum maximum Jacq. cv. Tanzânia 1) and legumes (Arachis pintoi Koprov & Gregory. cv. Amarillo and Glycine wightii Verdc.) was evaluated. The forages were sampled in Spring, Summer and Winter, with four replications per species per season. The n-alkanes C24 to C35, using C32 and C34 as internal markers, were considered in the analyses. Concentrations of n-alkanes in these species and their respective fractions (leaf blade, top and bottom portions of the stem and dead matter for grasses; leaves, top and bottom of stem and dead matter for legumes) were evaluated by multivariate analysis. The discriminatory potential of n-alkanes was determined by the canonical variables analysis. The species and their respective fractions were divided into groups by cluster analysis. N-alkanes with the smallest potential discriminatory potential were: C26, C29, C25, C27 and C28 (spring), C26, C28, C27, C30 and C29 (summer) and C28, C26, C25, C29 and C27 (winter). The n-alkanes in the spring and winter samples allowed discrimination of Coast-cross leaf blade from the top and bottom stems portions of this grass and between grass and legumes. It was possible to discriminate fractions of nutritional importance of Brachiaria brizantha, leaf blade and higher portion of stem in the summer. The multivariate analysis, the canonical variables and the cluster analysis are good procedures to be used in n-alkanes studies for herbivores diets discriminating.
canonical variables; cluster analysis; composition of diets; markers; ruminates nutrition
