Effect of water spinach (Ipomoea aquatica) and cassava leaf meal (Manihot esculenta Crantz) with or without biochar on methane production in an in vitro rumen incubation using ensiled or dried cassava root meal as source of carbohydrate

Abstract

The objective of this study was to evaluate the effect of source of protein as cassava leaf meal or water spinach and supplementation with or without biochar on methane production in an in vitro rumen incubation system using ensiled or sun-dried cassava root as the source of energy. The experimental design was a 2*2*2 factorial in a completely randomized design with 8 treatments and 4 replications. The factors were: ensiled or sun-dried cassava root; water spinach meal or cassava leaf meal and with or without biochar. Urea was added as NPN source at 3% of substrate DM. The total substrates equivalent to 12g DM were put in the incubation bottle, followed by 960 ml of buffer solution and 240 ml of rumen fluid obtained from a cow immediately after being slaughtered. The bottles were then filled with carbon dioxide and incubated at 38 0C in a water bath for 48 hours with measurements of total gas production and methane percentage at intervals of 6, 12, 18, 24 and 48 h and determination of residual unfermented substrate DM at the end. The gas production was lower for ensiled than for dried cassava root; lower for cassava leaves than for water spinach; and lower for presence of biochar in the substrate. The percent methane in the gas and the percent DM mineralized followed the same pattern. The proportion of methane in the gas increased with the length of the incubation. It is proposed that the lower net production of methane per unit substrate DM digested, for cassava leaf meal compared with water spinach meal, was because of the lower solubility of the protein in the cassava leaf meal (25.6%) compared with the water spinach (66.3%) and that this retarded the fermentation of the substrate and particularly of methane formation.