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 CH 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 (NH Cl), 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 CH production and CH /total VFA ratio. The increases in CH production 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 CH /total VFA ratio with STAR, whereas CH /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 CH respectively. The results indicate the generation of CH from protein fermentation, and that the response of CH production to protein-N supply may differ with the basal substrate.

Effect of cellobiose and dietary soluble fibre on fermentation, growth performance and health in rabbits

“…These authors also noticed that using different blanks (with or without enzymes added) for correcting gas production values altered the differences between experimental treatments and changed the interpretation of results. The increased total VFA production and the shifts in VFA profile observed in our study when the blanks were pre-digested also indicated a fermentation of enzymes, as the amino acids resulting from proteolysis can be deaminated and the generated carbon skeletons be fermented to VFA (Van Soest, 1994;Vanegas et al, 2017). The greater isovalerate proportions detected in the predigested blanks are consistent with this hypothesis, because this VFA generally arise from the fermentation of leucine (Wallace and Cotta, 1988).…”

Protecting protein against ruminal degradation could contribute to reduced methane production

“…The experimental diets were formulated to contain a high proportion of cereal grains (62.2 and 45.2% for low‐ and high‐protein diets respectively) because Vanegas, González, et al. () observed that the contribution of protein fermentation to CH 4 production was greater with a rapidly fermentable substrate (starch) than with a slowly fermentable substrate (cellulose). Diets with two different CP levels were formulated to analyse the possible interaction between treatment and CP level.…”

“…Dietary characteristics are one of the most important factors influencing CH 4 production, and it is well known that diets rich in structural carbohydrates yield higher CH 4 emissions compared with those high in non‐structural carbohydrates (Kumar et al., ). A recent in vitro study (Vanegas, González, & Carro, ) showed the generation of CH 4 from pure protein fermentation and that the response in CH 4 production to protein supply differed with the basal substrate, being higher for a rapidly fermented substrate than for a slowly fermented one. In addition, the protection of sunflower protein against ruminal degradation by a combined treatment of malic acid and heat resulted in a reduction of in vitro CH 4 production that was attributed to reduced protein degradation (Vanegas, Carro, Alvir, & González, ; Vanegas, González, Alvir, & Carro, ).…”

In vitro caecal fermentation of carbohydrate-rich feedstuffs in rabbits as affected by substrate pre-digestion and donors' diet

“…and the generated carbon skeletons be fermented to VFA (Van Soest, 1994;Vanegas et al, 2017). The greater isovalerate proportions detected in the pre-digested blanks are consistent with this hypothesis, as these VFA generally arise from the fermentation of leucine (Wallace and Cotta, 1988).…”