Analysis Of The Effect Of Nutritional Regulation On The Performance Of Beef Cows Based On 16S RRNA And Metabolomics

In this study,beef cows at different growth stages were used as experimental animals to study the effects of concentrated feed on feed intake,growth and development,blood nutrient metabolism indicators,rumen fermentation and rumen flora composition in grazing cattle under grazing conditions.The effect of the dietary concentrate ratio on the body condition,serum reproductive hormone content,oestrus rate,rumen fermentation and flora composition of empty-bearing cows,and the effect of different dietary energy levels on feed intake,body condition,energy metabolism and perinatal cows was investigated along with the effect of serum differential metabolites.This provides important data and theoretical support for dietary matching and nutritional regulation of beef cows in China.This thesis is divided into three parts.The first part includes experiment 1 and experiment 2,which addressed the effects of concentrated feed on the growth and development,blood indicators,rumen fermentation,rumen flora composition and serum differential metabolites of growing cattle under grazing conditions.A selection of 24 healthy 7-month-old Simmental cows with similar body size and weight were randomly divided into two treatment groups: the grazing group and the supplementary feed group according to the principle of homogeneity.The grazing group grazed on natural pasture,and the supplementary feed group was supplemented with concentrate under the same grazing conditions.The pretrial period was 8 days,and the trial period was 60 days.The results showed that concentrate supplementary feeding significantly increased the total dry matter intake and average daily gain of the growing cattle and reduced the forage intake and the feed-to-weight ratio.In terms of body size indicators,supplementary feeding concentrates significantly increased the body height and oblique body length of the bred cattle;during the entire supplementary feeding period,the average daily gain of the supplementary feed group was more than 1.5 times that of the grazing group.In terms of serum biochemical indicators,supplementation with concentrate significantly increased the concentrations of thyroid hormone,glucose,insulin,growth hormone and insulin-like growth factor-1 in the serum of grazing cattle.Concentrate supplementation significantly increased the concentration of rumen ammonia nitrogen,propionic acid,butyric acid and total volatile fatty acids and reduced the ratio of acetic acid/propionic acid but had no effect on the rumen p H of grazing cattle.The abundance of the rumen flora in the supplementary feed group was significantly higher than that of the grazing group;the dominant phyla in the rumen of the supplementary feed group and the grazing group were Bacteroides and Firmicutes;the concentrate supplement significantly reduced the abundance of Bacteroides and significantly increased the ratio of Firmicutes/Bacteroidetes.The relative abundance of Rikenellaceae?RC9?gut?group,norank?f??UCG-011 and norank?f??UCG-010 in the rumen of the grazing group was significantly higher than that of the supplementary feed group,and the relative abundance of Succiniclasticum tended to be higher than that of the supplementary feed group.Vibrio butyricum was also found in the rumen of the supplementary feed group at significantly higher relative abundance than that of the grazing group.The serum total protein,triglyceride and leptin levels of the supplementary feed group were significantly higher than those of the grazing group.A total of 45 serum metabolites were identified as significantly different metabolites between the two groups.The enrichment analysis results showed that arginine biosynthesis,tryptophan metabolism and glycerophospholipid metabolism were significantly enriched between the two groups.The main metabolic pathways affected are related to energy and amino acid metabolism.Concentrate feeding significantly changes the metabolism of sugar,lipids and protein,which helps the growth of heifers.The second part of this report includes experiment 3,which studied the effects of different dietary concentrate levels on the body condition,serum reproductive hormone content,oestrus rate,body health,rumen fermentation and flora composition of empty cows.Using a completely random design method,90 lean cows(average weight387.2±22.6 kg)were divided into 3 groups,and they were fed high-concentrate diets(65:35,HCD),medium-concentrate diets(50:50,MCD)and low-concentrate diets(35:65,LCD).During the experiment,each treatment group was allowed free intake.The results showed that the dry matter intake and dry matter digestibility both increased significantly with increasing concentrate level.The digestibility of organic matter and crude protein in the HCD group was higher than that in the LCD group,and the digestibility of neutral detergent fibre in the LCD group was significantly higher than that of the other two groups.The serum glucose content of the HCD group and the MCD group was significantly higher than that of the LCD group at 20 d and 60 d of the trial period;at 40 d,the serum urea nitrogen content of the LCD group was significantly higher than that of the other two groups.Compared with the LCD group,the serum reproductive hormone concentration,the number of oestrus cycles and the spontaneous oestrus rate of the HCD and MCD groups were significantly increased;in addition,the average oestrus time of the test cattle in each group in the MCD group was significantly less than that of the LCD group during the entire test period.Increasing the level of concentrate in the diet reduced the p H of the rumen and significantly increased the concentration of ammonia nitrogen,butyric acid and isovaleric acid in the rumen fluid;compared with that of the LCD group,the concentration of propionic acid in the rumen fluid of the HCD group increased significantly,and the concentration of acetic acid was significantly reduced.The concentration of lipopolysaccharide in rumen fluid increased significantly with increasing concentrate levels.The plasma concentrations of lipopolysaccharide,CRP,HP and SAA in the HCD group were significantly higher than those in the other two groups.The diversity and richness of the rumen flora in the HCD group were significantly lower than those of the other two groups.With increasing concentrate level,the relative abundances of Bacteroidetes,Fibrobacterota,Prevotella and Prevotellaceae UCG-003 decreased,and the relative abundances of the Ruminococcaceae NK4A214 group,Saccharofermentans and Spirochaetota increased.The third part of this report includes experiment 4 and experiment 5.Ninety healthy Angus cows with similar gestation days and body weights were selected as experimental animals,and they were randomly divided into 3 treatment groups.The test diet was formulated according to the formula recommended by the beef cattle NRC(2000)and was prepared according to the nutritional requirements of 500 kg beef cattle at 9 months gestation.The three groups of diets were prepared according to the principle of nitrogen-energy balance,respectively,with levels of 0.90×NRC(low energy group),1.00×NRC(medium energy group)and 1.10×NRC(high energy group)recommended energy level diets.During the whole experiment,each group was fed the total mixed ration(TMR)according to the ratio of concentrate to roughage of 40:60.The results showed that the DMI of the HE cows was higher than that of the ME and LE groups at 45-7 days before delivery;the DMI of the LE cows was significantly higher than that of the HE group within 7 days after delivery.The prenatal NEI of the HE group was significantly higher than that of the ME and LE groups,and the postpartum NEI of the HE group was significantly higher than that of the LE group.The weight gain rate of the HE cows before delivery was significantly higher than that of the LE group,but there was no significant difference from the ME group.The weight loss of the HE cows at 35 d postpartum was significantly lower than that of the ME and LE groups.The postpartum weight change and the prepartum BCS change of the HE group were significantly higher than those of the other two groups.Compared with the other two groups,the first mating time after childbirth in the HE group was significantly shortened.The effect of dietary energy level on perinatal cows was analysed by liquid chromatography-time-of-flight mass spectrometry with serum metabolomics technology.The results showed that the metabolites and metabolic pathways in this experiment underwent significant changes.From all identified metabolites,51 different plasma metabolites between the two groups were screened out.Among them,22 metabolites were significantly downregulated in the HE group,and 29 metabolites were significantly upregulated.The qualitative fatty acids in the plasma,such as citric acid,linoleic acid,nonanoic acid,hexadecanedioic acid,heptadecanoic acid and lyso PE(0:0/18:0),were downregulated in the HE group.In addition,the relative expression levels of metabolites such as inosine,L-isoleucine,?-methylphenylalanine and glutamine in the HE group were higher than those in the control group.The four metabolic pathways of linoleic acid metabolism,galactose metabolism,valine,leucine and isoleucine biosynthesis,and glycerophospholipid metabolism were significantly enriched between the two groups of test cattle.In general,the altered metabolic pathways mainly involved amino acid biosynthesis and carbohydrate and fatty acid metabolism.