| The objective of the current study was to evaluate the effect of live yeast (5. cerevisiae, CNCM1-1077, Lallemand, Toulouse, France) on rumen fermentation and nutrient degradation in steers fed diets with different concentrate to forage ratios (CTFR); the mechnism of S. cerevisiae (SC) affect nutrient degradation was studied through the effect of SC on fibrolytic activities and rumen microbial populations. Effect of SC on plasma metabonomics in steers fed diets with different concentrate to forage ratios (CTFR) was studied at the same time. Ten Simental x Local breed steers (450±50kg BW) fitted with rumen fistulas (10cm diameter) were assigned to control and treatment groups. Steers in the two groups were fed the same basal diets but the treatment groups received supplementation with SC (8×109cfu/h/day through the ruminal fistula) following a2-period crossover design. Each period consisted of four phases, each of which lasted17days:16days for dietary adaptation, and1day for rumen sample collection. From the1st to the4th phase, steers were fed in a stepwise fashion with increasing CTFRs, i.e.,30:70,50:50,70:30, and90:10. MIXED procedure was used to analysis effect of dietary CTFR and SC supplementation on peremeters. Linear and quadratic responses for dietary CTFR were assessed using orthogonal polynomial contrast statements.Experiment1:The objective was to assess the effects of S. cerevisiae on rumen fermentation characteristics of steers fed diets with different CTFRs. With CTFR increasing, rumen fermentation characteristics presented quadratic variation trend. Ruminal pH, molar proportion of acetate and isobutyrate, and A:P linearly decreased (L; P<0.01); TVFA concentration, molar proportion of propionate, butyrate, valerate and isovalerate linearly increased (L; P<0.01); ammonia N and lactate concentration presented quadratic variation (Q; P<0.01). Ruminal pH in the SC groups was higher than the control (P<0.05). There were no difference in concentrations of TVFA, ammonia N and D+L-lactate, and in VFA molar proportion between SC supplementation and control groups. These results showed that dietary concentrate to forage ratios significantly affect rumen fermentation characteristics; SC supplementation increased rumen pH, but has no effect on rumen ammonia N, TVFA and lactate concentration or rumen fermentation pattern.Experiment2:The objective was to assess the effects of S. cerevisiae supplementation on nutrient degradation of steers fed diets with different CTFR. With CTFR increasing, steam-flaked corn DM disappearance rate at each time point presented quadratic variation trend (Q; P<0.01); rapidly degradable fraction (aDM,aNDF) of the three fibrous feedstuffs quadraticly decreased (Q; P<0.01); degradation rate (cDM, cNDF) and effective degradability (EDDM, EDND) linearly decreased (L; P<0.01). SC supplementation decreased3h,6h and12h corn DM disappearance rate (P<0.05), but had no effect on24h and48h disappearance rates (P>0.05). There were no difference in CRH aDM, bDM,aNDF between SC supplementation and control groups; CRH BNDF was lower than control groups (P<0.05); CRH cDM, EDDM,cNDF and EDNDF were higher than control groups (P<0.05). There were no differences (P>0.05) in alfalfa aDM, bDM, EDDM, aNDF and bNDF between the two groups, but cDM, cNDF and EDNDF were higher (P<0.05) than control groups.There was no differences (P>0.05) for silage maize stalk degradation characters between two groups. The results showed that dietary CTFR significantly affect nutrient degradation. SC supplementation enhanced fibrous feedstuff degradation rate and effective degradability.Experiment3:The objective was to assess the effects of S. cerevisiae supplementation on fibrolytic activities and rumen microbial populations of steers fed diets with different CTFR. With CTFR increasing, microbial popolations presented in linear or quadratic variation trend but fibrolytic activities linearly increased. Compared with the control group, there was an increasing trend of rumen fungi and protozoa in SC group (P<0.1); copies of total bacteria in SC group were significantly higher (P<0.05). Additionally, percentage of Ruminobacter amylophilus was significantly lower (P<0.05) but percentage of Selenomonas ruminantium was significantly higher (P<0.05) in the SC group. Compared with control,S. cerevisiae supplementation gave higher activities of xylanase and avicelase (P<0.05) as well as β-glucanase activity (P<0.1), but had no effect on carboxymethyl cellulose activity (P>0.05). Overall, S. cerevisiae supplementation increased rumen total bacteria, fungi, protozoa, and lactate-utilizing bacteria but reduced starch-degrading and lactate-producing bacteria; S. cerevisiae supplementation increase enzyme fibrotic activities.Experiment4:The objective was to assess the effects of S. cerevisiae supplementation on plasma metabonomics of steers fed diets with different CTFR. UPLC-QTOFMS was used to detecte plasma metabonomics. PCA, PLS-DA and OPLS-DA was used to filtrate biomarkers.The results showed that biomarkers among different dietary CTFR groups were cytosine, dihydrothymine, palmitic amide, stearamide, oleamide, D-4’-phosphopantothenate. Dietary CTFR at30:70, biomarkers between SC supplementation and control groups were Sphinganine, Phytosphingosine, PC (18:0). Dietary CTFR at50:50, biomarkers between the two groups were13E-docosenamide,1-monoacylglycerol, PC(16:0). Dietary CTFR at70:30, biomarkers between the two groups were diacylglycerol,1-monoacylglycerol, triacylglycerol, PC (18:0), PC (17:0). Dietary CTFR at90:10, biomarkers between the two groups were13E-docosenamide, glycocholic acid, PC (18:2), PC (20:2). The results show that with concentrate level increasing, fat metabolism was improved, which was benifical to improve production performance, but rumen wall damage may be aggravating; SC supplementation improved phospholipid and fat metabolism, which is beneficial to maitain animal health status and improve production performance. |
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