Evaluation of tropical legumes: chemical composition, in vitro degradability, and ingestive selectivity by bovines and caprines. [Spanish]Original Title Evaluacion forrajera de leguminosas tropicales: composicion quimica, degradabilidad in vitro y selectividad ingestiva por bovinos y caprinos.

摘要

An experiment, divided into three trials, was conducted to determine the chemical composition, in vitro degradability, and ingestive selectivity of the tropical legumes (TL) Stylosanthes guianensis (Stylo; SG), Cajanus cajan (pigeon-pea; CC) and Arachis glabrata (rhizome perennial peanut; AG). In the first trial the organic matter (OM), inorganic matter (IM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF, hemicelulose), cellulose, lignin and acid detergent insoluble nitrogen (ADIN) content in the whole plant and botanical components (stems and leaves) of the three TL were determined. The second trial evaluated the in vitro apparent (AIVDMD) and true dry matter degradability (TIVDMD) of the three TL during 48 h of incubation in bovine and caprine ruminal fluid. Trial three, of cafeteria type, evaluated the voluntary intake by goats and heifers of the three TL during one hour. In all trials tropical grass hay (HG) was used as control forage. A qualitative scale (none, low, medium and high) was used to express the intake of TL and GH. Organic matter content was lower (P<0.05) but IM was higher (P<0.05) in AG than in CC, SG, and GH. In all three TL, the CP content was higher (P<0.05) than in TG, but NDF was lower (P<0.05). Among TL species, CP content was higher (P<0.05) in AG than in SG and CC, but NDF content was similar. ADF content was also lower (P<0.05) in AG than in CC and in SG, but hemicelulose percentage was higher (P<0.05). Lignin was lower (P<0.05) in GH than in the three legumes, and CC showed the highest (P<0.05) ADIN content among the forages evaluated. For all three TL, CP in leaves was higher than 20%. Leaf NDF content was lower (P<0.05) in CC than in AG and in SG, whereas ADF was higher (P<0.05) in SG than in AG and CC. Leaves of AG also had higher (P<0.05) hemicelulose but lower (P<0.05) cellulose values than CC and SG. Lignin content was similar in leaves of the three TL, but ADIN content was higher (P<0.05) in CC. Crude protein content of stems was lower (P<0.05) in CC than in AG and SG. The NDF content and its fractions (ADF, cellulose and hemicelulose) were lower (P<0.05) in AG stems than in those of SG and CC. The highest (P<0.05) lignin content and lowest (P<0.05) ADIN content were observed in CC and SG stems, respectively. In the second trial, use of either ruminal inoculum type gave AIVDMD and TIVDMD values that were, in descending order, highest (P<0.05) in AG than in SG, GH and CC. In trial three a greater intake was observed in goats and heifers offered AG and GH than when offered SG and CC. Based on nutrient content, in vitro dry matter degradability, and voluntary intake, AG showed greater potential as a forage source than SG and CC. However, all three TL showed promise as potential alternatives for use as an integral part of ruminant feeding systems in the tropics.