Abstract: [Objective] This study was conducted to investigate the effects of feeding corn straw treated with different methods as roughage on methane emission and rumen function in beef cattle. [Method] Seventeen-month-old healthy Grassland Red cattle （n=3） and Yanbian Yellow cattle （n=3） with an average weight of （375±5） kg were selected. The feeding trial with two-factor experimental design was composed of two stages and each had a pre-feeding period of 15 days and a formal-feeding period of 3 days. In the first stage, Grassland Red cattle fed corn straw silage as roughage （QH group） and Yanbian Yellow cattle fed dry corn straw as roughage （JY group）. In the second stage, Grassland Red cattle fed dry corn straw as roughage （JH group） and Yanbian Yellow cattle fed corn straw silage as roughage （QY group）. The initial and final weights as well as feed intake of the experimental cattle were recorded, and the average daily gain and dry matter intake was calculated. An open reflux respiratory calorimetry device for large animal were used to determine the methane emission. Rumen fluid samples were collected to evaluate pH value as well as the contents of ammonia nitrogen, rumen microbial protein, total volatile fatty acids, acetic acid, propionic acid, and butyric acid. In addition, the rumen microflora was characterized using 16S rDNA high-throughput sequencing, and the rumen fluid metabolites were assessed using non-targeted metabolomics. [Result] ① Yanbian Yellow cattle had extremely significantly （P<0.01） higher final weight and average daily gain as well as extremely significantly （P<0.01） lower dry matter intake in comparison to Grassland Red cattle, while no significant （P>0.05） difference in the methane emission was observed between the two cattle breeds. QH and QY groups had extremely significantly （P<0.01） increased final weight, average daily gain and dry matter intake as well as extremely significantly （P<0.01） decreased methane emission in comparison to JH and JY groups. ②The rumen fermentation parameters of Grassland Red cattle were not significantly （P>0.05） different from those of Yanbian Yellow cattle. Compared with JH and JY groups, QH and QY groups exhibited extremely significantly （P<0.01） reduced rumen fluid pH value, contents of ammonia nitrogen, acetic acid and butyric acid, and ratio of acetic acid to propionic acid, while exhibited extremely significantly （P<0.01） elevated contents of rumen microbial protein, total volatile fatty acids, and propionic acid. ③ Firmicutes, Proteobacteria and Bacteroidetes were observed as the dominant rumen microbial phyla in the four groups, with total relative abundance from 73.75% to 81.22%. The cattle breeds, corn straw treatment methods and the interaction between these two factors had no significant （P>0.05） effects on the relative abundance of rumen microflora at phylum level. Compared with JH and JY groups, extremely significantly （P<0.01） higher relative abundance of Succiniclasticum, Butyrivibrio and Ruminococcus as well as extremely significantly （P<0.01） lower relative abundance of Clostridiaceae_Clostridium and Prevotella was observed in QH and QY groups. The cattle breeds, corn straw treatment methods and the interaction between these two factors had no significant （P>0.05） effects on the relative abundance of rumen microflora at genus level. ④ A total of 525 secondary differential metabolites were screened from rumen metabolites of different groups, among which 10 were significantly different. Quinolinic acid, fumaric acid, cortisone, L-glutamic acid, phenyllactate, L-carnitine, and catechol were significantly enriched in 9 pathways. Fumaric acid was significantly enriched in tryptophan metabolism, central carbon metabolism in cancer, arginine biosynthesis, and phenylalanine metabolism pathways. The correlation analysis between the relative abundance of rumen microflora at genus level and the concentrations of differential metabolites in rumen fluid showed an extremely significantly （P<0.001） negative correlation between the concentration of fumaric acid and the relative abundance of Prevotella. [Conclusion] Feeding corn straw silage as roughage was able to effectively control the methane emission, increase the daily weight gain, ameliorate the rumen fermentation function, and decrease the relative abundance of Prevotella in rumen in beef cattle. In addition, the lower methane emission of the beef cattle fed corn straw silage as roughage was attributed to the elevated concentration of fumaric acid in rumen fluid.

Key words: beef cattle, roughage, corn straw, methane emission, rumen microflora, metabolite difference