Examination of microbial degradation of Ficus exasperata leaves and cassava peels by in situ incubation and scanning electron microscopy

Abstract

Microbial digestion of cassava ( Manihot esculenta) peels and Ficus exasperata leaves was studied in a randomised incomplete block experiment involving six ruminally fistulated Djallonké wethers. The wethers were fed sun-dried cassava peels ad libitum, plus supplements of 0 (control), 50, 100, 150, 200 or 250 g day −1 of sun-dried Ficus exasperata leaves. Peels and leaves were ground (2 mm) for ruminal incubation to determine in situ disappearances of dry matter (ISDMD) and nitrogen (ISND), and chopped (25 mm 2) for examination of incubation residues by scanning electron microscopy. Unincubated Ficus exasperata leaves were also examined by energy dispersive X-ray analysis (EDXA). In situ DMD and ISND from both materials were maximal within 48 h. Ficus leaf supplementation increased the soluble, slowly degradable, and potentially degradable fractions of DM and N in peels and in leaves ( p < 0.05). At 250 g day −1, supplementation increased the soluble and potentially degradable DM fractions of cassava peel from 12.8 and 55.9% (in controls) to 18.1 and 68.2% ( p < 0.05), and increased the soluble and potentially degradable N fractions from 13.7 and 53.1% to 17.5 and 64.2%, respectively ( p < 0.05). The 250 g daily supplement increased potentially degradable DM and N fractions of ficus leaves from 72.5 and 62.6% (in controls), to 78.7 and 74.1%, respectively ( p < 0.05). The fractional rate of N disappearance from cassava peels increased ( p < 0.05) with increasing level of supplementation. Lag times for ISDMD and ISND from ficus leaves decreased ( p < 0.05) when the diet included ficus. Ficus leaf supplementation did not affect ruminal pH, or total or cellulolytic bacterial numbers ( p > 0.05). Cassava peel corky periderm was extremely resistant to microbial attack, whereas colonization and digestion of the cortex was evident within 4 h. Intact ficus leaves were resistant to colonization, with microbial attachment restricted to damaged regions. Examination by EDXA revealed uniform distribution of silica within the entire epidermis of the ficus leaf, except in the trichomes. Supplementing a cassava peels-based diet with Ficus exasperata leaves improved ruminal degradability of the peels, and may increase feeding value of this agricultural by-product.