Influence of protein fermentation and carbohydrate source on in vitro methane production
J. L. Vanegas, J. Gonzalez and M. D. Carro Incubations were carried out with batch cultures of ruminal micro-organisms from sheep to analyse the influence of the N source on in vitro CH4 production. The two substrates were mixtures of maize starch and cellulose in proportions of 75:25 and 25:75 (STAR and CEL substrates, respectively), and the three nitrogen (N) sources were ammonia (NH4Cl), casein (CA) and isolated soya bean protein (SP). Five isonitrogenous treatments were made by replacing non-protein-N (NPN) with CA or SP at levels of 0 (NPN), 50 (CA50 and SP50, respectively) and 100% (CA100 and SP100) of total N. All N treatments were applied at a rate of 35 mg of N/g of substrate organic matter and incubations lasted 16.5 h. With both proteins, N source 9 substrate interactions (p = 0.065 to 0.002) were detected for CH4 production and CH4/total VFA ratio. The increases in CH4 production observed by replacing the NPN with protein-N were higher (p < 0.05) for STAR than for CEL subst
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