The Effect of γ-Aminobutyric Acid Addition on In Vitro Ruminal Fermentation Characteristics and Methane Production of Diets Differing in Forage-to-Concentrate Ratio

Abstract

Gamma-aminobutyric acid (GABA), known as the most abundant inhibitory neurotransmitter in the mammalian brain, can permeate ruminal epithelia by passive diffusion and enrich in the rumen environment. To explore whether the addition of GABA can regulate rumen fermentation characteristics as well as methane production, a 2 × 6 factorial in vitro rumen batch culture was conducted to determine the supplemental effect of GABA at inclusion levels of 0 (Control), 10, 20, 30, 40 and 50 mg in culture fluids on rumen fermentation of two total mixed rations (HF—a high-fiber ration consisted of 70% corn silage and 30% concentrate; and LF—a low-fiber ration consisted of 30% corn silage and 70% concentrate). After 72 h in vitro incubation of two rations with mixed rumen microoganisms obtained from five rumen-cannulated lactating Holstein dairy cows, increasing GABA addition linearly increased cumulative gas production in the LF group, though in vitro dry matter digestibility was not affected in either the LF or HF group. Kinetic gas production analysis noted that increasing GABA addition mostly decreased the gas production rate (i.e., RmaxG), as well as the ration digestion rate (RmaxS) to reach maximum fermentation. The GABA addition did not affect pH or microbial growth (i.e., MCP). However, total volatile fatty acid production in both LF and HF groups all linearly increased with the increase in GABA addition. Along with the increase in GABA addition in both LF and HF groups, the ratio of non-glucogenic to glucogenic volatile fatty acids both increased, while the molar proportions of propionate and valerate were significantly decreased, and the acetate and butyrate proportions were increased after 72 h in vitro rumen fermentation. The time-course change of fermentation end-products generally showed that carbon dioxide declined from approximately 89% to 74%, and methane increased from approximately 11% to 26%. After 72 h in vitro fermentation, molar methane proportion was greater in the LF than in the HF group, and increasing GABA addition quadratically increased methane production in the LF group while a slight increase occurred in the HF group.

The Effect of Guanidinoacetic Acid Addition on In Vitro Rumen Fermentation Characteristics and Gas Production of Early- and Late-Stage Sheep-Fattening Diets

“…Moreover, gas production is affected by the substrate's chemical composition and feed type [34]. DM digestibility is typically used to determine how the feed is degraded [25]. In the current study, the change in cumulative gas production at 72 h (GP 72 ), asymptotic gas production (A), and the time at which half of A is reached (C) coincided with the change in DM digestibility.…”

“…A 1 mL subsample was mixed with 0.25 mL of meta-phosphoric acid (250 g/L), which was centrifuged at 20,000× g for 15 min and filtered using a 0.22 µm syringe filter to determine the total volatile fatty acid (TVFA). The TVFA content was analyzed using gas chromatography (HPGC; GC-128; INESA Corporation) with a hydrogen flame detector and a capillary column (FFAP, Zhonghuida Instruments Co., Ltd., Dalian, China; 50 m long, 0.32 mm diameter, 0.50 µm film) as described by Wang et al [25]. As described by Bremner and Keeney [26], ammonia nitrogen (NH 3 -N) was measured at 660 nm following a spectrophotometric method.…”

Effect of Tea Seed Oil on In Vitro Rumen Fermentation, Nutrient Degradability, and Microbial Profile in Water Buffalo

“…This is highly variable and depends on many factors, such as plant species, stage of growth, parts of a plant, and extraction method [ 47 ]. Rumen microorganisms can degrade crude protein from feed and saliva to produce ammonia, small peptides, and amino acids, and use these degradation products as nitrogen sources to synthesize MCP [ 48 , 49 , 50 ]. In the rumen, the MCP level usually reflects the growth rate and the population of rumen microbes [ 49 ].…”

“…Rumen microorganisms can degrade crude protein from feed and saliva to produce ammonia, small peptides, and amino acids, and use these degradation products as nitrogen sources to synthesize MCP [ 48 , 49 , 50 ]. In the rumen, the MCP level usually reflects the growth rate and the population of rumen microbes [ 49 ]. The increase in MCP observed in response to TSO treatments in the present study is favorable, particularly in the case of the T2 and T3 groups, suggesting the positive effect of TSO on microbial populations.…”