Objective This experiment aims to evaluate the feeding value of yeast culture for white distiller's grains (YCDG) and explore the effects of different proportions of bran substitution on the gas production, gas composition, fermentation parameters and nutrient degradation rate of artificial rumen in dairy cows, providing a basis for the scientific application of YCDG.

Method The test consists of two parts. Firstly, the same batch of YCDG is divided into three independent samples by the quartering method, and the contents of conventional nutrients, minerals, vitamins and mycotoxins are determined respectively. Then, the in vitro batch culture method was adopted, and the wheat bran in the TMR substrate was replaced with 0% (CON), 1% (T1), 2% (T2), 3% (T3), and 4% (T4) YCDG in equal proportions, respectively. The gas production and gas composition at different time points were determined by using an automatic gas production recording device for in vitro fermentation. The fermentation broth and substrates were collected at the 24 and 48 h of fermentation respectively to measure the nutrient degradation rate, fermentation parameters and gas composition.

Result The crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) contents of YCDG were relatively high, and the contents of each mycotoxin were all lower than the international standard limits. Compared with the CON group, YCDG increased the gas production during in vitro fermentation (P<0.05). The gas production in the T3 group was the highest during 2–12 h (P<0.05), and that in the T2 group increased significantly at 2–8 h (P<0.05). The concentrations of methane and carbon dioxide in group T3 were the highest (P<0.05), and the concentrations of oxygen and nitrogen were the lowest (P<0.05). The pH of group T4 at 48 h was significantly higher than that of groups CON, T1 and T2 (P<0.05), and the pH of group T3 was significantly higher than that of group CON (P<0.05). The concentrations of acetic acid, isobutyric acid and butyric acid in group T3 were higher than those in groups T1, T2 and T4 (P<0.05). The acetate-to-propionate ratio and the molar proportion of acetic in group T4 were both significantly higher than those in the other groups at 24 and 48 h (P<0.05).The degradation rates of dry matter, CP, NDF and ADF among each group were not significantly affected.

Conclusion This study concluded that YCDG is rich in nutrients and safe in quality. Replacing bran with an appropriate amount of YCDG in the fermentation substrate can promote gas production in the early stage of artificial rumen fermentation and improve rumen fermentation parameters, a substitution level of 2%–3% is recommended.