title: Influence of protein fermentation and carbohydrate source on in vitro methane production.
abstract: Incubations were carried out with batch cultures of ruminal micro-organisms from sheep to analyse the influence of the N source on in vitro CH4production. 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 × substrate interactions (p = 0.065 to 0.002) were detected for CH4production and CH4/total VFA ratio. The increases in CH4production observed by replacing the NPN with protein-N were higher (p < 0.05) for STAR than for CEL substrate, but the opposite was observed for the increases in volatile fatty acid (VFA) production. As a consequence, replacing the NPN by increased levels of CA or SP led to linear increases (p < 0.05) in CH4/total VFA ratio with STAR, whereas CH4/total VFA ratio tended (p < 0.10) to be decreased with CEL substrate. Increasing the amount of both proteins decreased linearly (p < 0.05) ammonia-N concentrations, which may indicate an incorporation of amino acids and peptides into microbial protein without being first deaminated into ammonia-N. In incubations with the tested N sources as the only substrate, the fermentation of 1 mg of CA or SP produced 1.24 and 0.60 μmol of CH4respectively. The results indicate the generation of CH4from protein fermentation, and that the response of CH4production to protein-N supply may differ with the basal substrate.
authors.affiliation: Departamento de Producción Agraria, E.T.S.I. Agraria, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, Madrid, Spain.
authors.forename: J L
authors.initials: JL
authors.lastname: Vanegas
authors.affiliation: Departamento de Producción Agraria, E.T.S.I. Agraria, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: González
authors.affiliation: Departamento de Producción Agraria, E.T.S.I. Agraria, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, Madrid, Spain.
authors.forename: M D
authors.initials: MD
authors.lastname: Carro
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D001419:Bacteria / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D005285:Fermentation; D008619:Mepivacaine / Q000378:metabolism*; D008697:Methane / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D012417:Rumen / Q000382:microbiology; D012756:Sheep / Q000382:microbiology*
chemical_list: D011506:Proteins; D008619:Mepivacaine; D008697:Methane
keywords: 
  in vitro
  ; methane; protein; rumen fermentation