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

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