Effect of soybean oil at different levels on rumen fermentation characteristics of beef cattle in vitro

The experiment was to explore the effect of soybean oil on ruminal fermentation characteristics of beef cattle by in vitro culture method. The experiment was divided into five groups. Total mixed ration with 0.5 g concentrate to forage ratio at 50∶50 was used as the fermentation substrate. Soybean oil was added at levels of 0 (control), 3%, 6%, 9% and 12% (dry matter basis), respectively. After fermented for 12, 24 and 48 h, determining total gas production, methane production and rumen fermentation parameters. The results showed that compared with the control group,the supplementation of 6%, 9% and 12% soybean oil significantly decreased total gas production and methane production after fermentation for 6 h (P<0.05), the concentration of ammonia nitrogen and microbial protein concentration was significantly decreased in 9% and 12% addition groups after fermentation for 24 h and 48 h (P<0.05). After fermentation for 12 h, the rumen fluid pH value in 6%, 9% and 12% addition groups was significantly higher than that of the control group (P<0.05). The concentration of total volatile fatty acids, acetic acid and propionic acid in 6%, 9% and 12% addition groups were significantly reduced after adding soybean oil for 12 h (P<0.05), the concentration of butyric acid in 9% and 12% addition groups was increased significantly after fermentation for 24 h (P<0.05), and the ratio of acetic acid/propionic acid in 6% addition groups was decreased significantly after fermentation for 24 h and 48 h (P<0.05). The experiment indicates that soybean oil can regulate ruminal fermentation and reduce methane production, but the over-high addition level has inhibition effect on ruminal fermentation. The optimal supplemental level is 3% under in vitro conditions.