Correlation Between Rumen Flora Composition And Amino Acid Metabolism In Simmental Cattle And Their Different Hybrid Combinations

In this study,Simmental cattle and their various crossbreeds will be utilized to explore differences in rumen flora composition and amino acid metabolism.This will be achieved through analyzing rumen flora,blood biochemistry indexes,and amino acid metabolism.The goal is to provide a theoretical framework for the practical application of hybrid beef cattle and related research.The specifics of the experiment are outlined below:Experiment 1: Nine healthy fattening cattle with similar body condition and feed intake were selected,including three Chinese Simmental cattle,three Simmental cattle and Chinese Holstein hybrid cattle(SH group),and three Simmental cattle and Mongolian cattle hybrid cattle(SM group).The experimental cattle were fed a mixed pen housing free-range and total mixed diet during the fattening period,which lasted for 180 days.The cattle were free to feed and drink during this period,and they were slaughtered at the Inner Mongolia Tianmuzhen Meat Industry Slaughterhouse according to standardized procedures.Rumen fluid was collected immediately after slaughter for sequencing and analysis of rumen shortchain fatty acids and rumen microbiota 16 S r RNA microorganisms.Results showed that there was no significant difference in rumen p H among the three groups(P>0.05).However,the acetic acid content in the rumen of the three groups of experimental cattle was significantly different,with Simmental having the highest content followed by SM group and finally SH group(P<0.01).The propionic acid content in the rumen of Simmental cattle was significantly higher than that in SH group and SM group(P<0.05).There was no significant difference in total SCFAs content between Simmental cattle and SM group,but they were both significantly higher than SH group(P<0.01).Additionally,there was no significant difference in the ratio of acetate to propionate between Simmental cattle and SM group,but they were both significantly higher than SH group(P<0.05).There was no significant difference in the contents of butyric acid,isobutyric acid,valeric acid,isovaleric acid,hexanoic acid and isohexanoic acid in the rumen of the three groups(P>0.05).At the OTU level,the three groups of test cattle shared 1396 OTUs,while there were 114 unique OTUs in Simmental cattle,43 in SH group,and 134 in SM group.Five dominant phyla with relative abundance greater than 1% were detected in the rumen flora of the three groups of cattle,with Bacteroidetes and Firmicutes being the most prevalent.A total of 28 dominant genera with relative abundances greater than 1% were identified in the experiment,including Prevotella,Succiniclasticum,Rikenellaceae＿RC9＿gut＿group,Prevotellaceae＿UCG-001,norank＿f＿F082,and NK4A214＿group.LEf Se analysis detected 15 rumen microorganism classes,orders,families,and genera.In the rumen of Simmental cattle,Oscillatoriaceae,g＿norank＿f＿UCG-010,f＿UCG-010,Papillibacter,norank＿f＿Bacteroidales＿BS11＿gut＿group,f＿Bacteroidales＿BS11＿gut＿group and Lachnospiraceae＿FCS020＿group were significantly enriched compared to other groups.In the rumen of the SM group,Treponema,Spirochaetes,and g＿unclassified＿f＿Lachnospiraceae were significantly enriched compared to other groups.In the rumen of SH group,the f＿Bacteroidales＿RF16＿group and g＿norank＿f＿Bacteroidales＿RF16＿group were significantly enriched compared to other groups.Experiment 2: During the slaughter,the live weight,average daily gain,carcass weight,and slaughter rate of each group were recorded,while blood samples were collected using a vacuum blood collection tube to prepare serum for the determination of serum biochemical indexes.The results revealed no significant difference in initial weight,final weight,carcass weight,slaughter rate,and average daily gain among Simmental,SH group,and SM group(P>0.05).However,the content of Cr,ALB,and the activity of AST in the serum of SM group were significantly higher than those of Simmental and SH group(P<0.05).Similarly,the activity of CPK in the serum of SM group cattle was significantly higher than that of Simmental cattle(P<0.05),but there was no significant difference with SH group(P>0.05).Conversely,there was no significant difference in the content of FAA,UN,TP,UA,and the activity of ALT in the serum of the three fattening cattle(P>0.05).The content of Ig M in the serum of SM group was significantly lower than that of Simmental and SH group(P<0.05),while the content of MDA in the serum of SM group was significantly higher than that of Simmental and SH group(P<0.05).Subsequently,the correlation between the top fifteen genera and serum biochemical indexes at the level of rumen flora in the three groups was analyzed.The results demonstrated a certain correlation between rumen bacteria and serum indexes.Experiment 3: After slaughter,the longissimus dorsi at the 12 th to 13 th ribs of the left carcass of each group were collected during the beef segmentation stage,and 22 amino acid metabolites were detected using LC-MS technology.The results indicated that all three groups had 22 amino acid metabolites in their longissimus dorsi,with two comparisons made between the three groups using Student’s t-test.One differential amino acid metabolite was detected in both Simmental cattle and SH group,while two differential metabolites were found in Simmental cattle and SM group.The concentration of L-Valine in the longissimus dorsi muscle of SH group was significantly lower than that of Simmental cattle(P<0.05),and the concentration of L-Cysteine and L-Valine in the longissimus dorsi of SM group was significantly lower than that of Simmental cattle(P<0.05).Experiment 4: Using the longissimus dorsi samples collected at the same time in Experiment 3,the expression differences of protein metabolism related genes in the mTOR signaling pathway of Simmental Cattle and their different combinations were compared based on RT-q PCR technology.The results showed that the amplification curves of the internal reference gene GAPDH and the target genes e IF4EBP1,Rheb,and NPRL2 in the longissimus dorsi of the three groups had a flat baseline period,obvious exponential period,smooth curve,and good repeatability of each multiple-well exponential period.The melting curves of each gene had a single peak at 85.77 °C,86.98 °C,80.97 °C,and 82.76 °C,respectively,indicating that the PCR product had good specificity.Compared with Simmental cattle,the m RNA expression of e IF4EBP1 gene in the longissimus dorsi of SM group was significantly increased(P<0.01),while no significant change was found in the longissimus dorsi of SH group(P>0.05).The expression of Rheb gene m RNA in the longissimus dorsi of SH group and SM group was significantly decreased compared with Simmental cattle(P<0.01).Furthermore,the m RNA expression of NPRL2 gene in the longissimus dorsi of SH group was significantly increased(P<0.05)compared with Simmental cattle,while it was significantly increased in the SM group(P<0.01).In summary,the different genetic backgrounds result in a significant change in the abundance of some Firmicutes and Bacteroidetes,which in turn affects the serum index,rumen metabolites,and protein synthesis rate in the longissimus dorsi of fattening cattle.Moreover,this effect may be attributed to the different activities of the mTOR signaling pathway in different genetic backgrounds.