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

Microbial digestion of cassava (Manihot esculenta) peels and Ficus exaspera ta leaves was studied in a randomised incomplete block experiment involving six ruminally fistulated Djallonke wethers. The wethers were fed sun-dried cassava peels ad libitum, plus supplements of 0 (control), 50, 100, 150, 2 00 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 disappearanc es of dry matter (ISDMD) and nitrogen (ISND), and chopped (25 mm(2)) for ex amination of incubation residues by scanning electron microscopy. Unincubat ed Fiats exasperata leaves were also examined by energy dispersive X-ray an alysis (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 potent ially degradable DM fractions of cassava peel from 12.8 and 55.9% (in contr ols) to 18.1 and 68.2% (p < 0.05), and increased the soluble and potentiall y degradable N fractions from 13.7 and 53.1% to 17.5 and 64.2%, respectivel y (p < 0.05). The 250 g daily supplement increased potentially degradable D M 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 disappearanc e from cassava peels increased (p < 0.05) with increasing level of suppleme ntation. Lag times for ISDMD and ISND from ficus leaves decreased (p < 0.05 ) when the diet included ficus. Ficus leaf supplementation did not affect r uminal pH, or total or cellulolytic bacterial numbers (p > 0.05). Cassava p eel corky periderm was extremely resistant to microbial attack, whereas col onization 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 s ilica within the entire epidermis of the ficus leaf, except in the trichome s. Supplementing a cassava peels-based diet with Ficus exasperata leaves im proved ruminal degradability of the peels, and may increase feeding value o f this agricultural by-product. Crown Copyright (C) 1999 Published by Elsev ier Science B.V.