Effects of combined addition of 3-nitrooxypropanol and vitamin B12 on methane and propionate production in dairy cows by in vitro-simulated fermentation
ABSTRACT The compound 3-nitrooxypropanol (3-NOP) is a promising methane inhibitor, which performs well in inhibiting methane emission and does not affect animal feed intake and digestibility. However, it causes a significant increase in hydrogen production while suppressing methane emission, resulting in a waste of feed energy. Vitamin B 12 is a key factor in the propionate production pathway and thus plays an important role in regulating the hydrogen utilization pathway. In this study, the effects of 3-NOP combined with vitamin B 12 supplementation on rumen fermentation and microbial compositional structure in dairy cattle were investigated by simulating rumen fermentation in vitro. Experiments were performed using a 2 × 2-factorial design: two 3-NOP levels (0 or 2 mg/g dry matter) and 2 vitamin B 12 levels (0 or 2 mg/g dry matter). Three experiments were performed, each consisting of 4 treatments, 4 replicates, and 4 blanks containing only inoculum. The combined supplementation of 3-NOP and vitamin B 12 reduced methane emission by 12% without affecting dry matter digestibility. The combined addition of 3-NOP and vitamin B 12 significantly increased the concentration of propionate and reduced the concentration of acetate and the acetate to propionate ratio. At the bacterial level, 3-NOP increased the relative abundances of Christensenellaceae_R-7_group and Lachnospiraceae_NK3A20_group . Vitamin B 12 increased the relative abundances of unclassified_f__Prevotellaceae and Prevotellaceae_UCG-003 and decreased the relative abundance of Lachnospiraceae_NK3A20_group . At the archaeal level, the combination of 3-NOP and vitamin B 12 increased the relative abundances of Methanobrevibacter_ sp._ Abm4 , OTU1125, and OTU95 and decreased the relative abundances of uncultured_methanogenic_archaeon_g__Methanobrevibacter , OTU1147, OTU1056, and OTU55. The results indicated that 3-NOP combined with vitamin B 12 could alleviate rumen hydrogen emission and enhance the inhibition of methane emission compared with 3-NOP alone.
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