Quality assessment of tropical browse legumes: Tannin content and protein degradation

Abstract

The in sacco digestibilities of dry matter and nitrogen content of the leaf material from 12 species of tropical browse legumes were measured in rumen-fistulated goats fed on a diet of rice straw supplemented with lucerne chaff. Freeze-dried samples of Albizia lebbek, Enterolobium cyclocarpum, Samanea saman and Sesbania sesban did not contain condensed tannins. These browse species also exhibited high digestibilities of both dry matter and nitrogen. Highest condensed tannin contents (vanillin-HCl method) were recorded in Calliandra calothrysus (11.07%) and Codariocalyx gyroides (7.12%). In species which contained tannins, however, there was poor correlation between nitrogen digestibility and total condensed tannin content (measured either by vanillin-HCl or butanol-HCl assay). Drying the browse at 60°C in a forced-draught oven resulted in variable losses in both total phenolics and condensed tannin content in all species. In particular, Gliricidia sepium and Tipuana tipu lost all apparent tannin content during oven drying. Lowest digestibilities of nitrogen (< 43%) were observed in Acacia aneura, Acacia angustissima, Albizia chinensis and Caliandra calothrysus. Oven drying of these species, however, resulted in highly significant increases in nitrogen digestibility.