| The objectives of the thesis were to study the effects of gallic acid(GA)and condensed tannins(CT)on in vitro nutrient disappearance,methane(CH4)production and rumen fermentation,and on nutrient digestibility,CH4 production and nitrogen(N)metabolism in beef cattle.Experiment 1 was conducted as a digestion and metabolism trial to investigate the effects of dietary supplementation of gallic acid(GA)on nutrient digestion,rumen fermentation,CH4 production,rumen microflora,N balance,N excretion pattern and urinary N constituents in beef cattle.In a 4 × 4 Latin square design,four male 30-month-old Simmental cattle(443 ± 22 kg live weight)with permanent rumen cannula received four levels of GA(purity ? 98.5%),i.e.0,5.3,10.5,21.1 g/kg dry matter(DM),added to a basal ration.Each experimental period lasted 17 d,consisting of 12 d adaptation and 5 d sampling.Supplementation of GA at 10.5 or 21.1 g/kg DM decreased the CH4 production(P<0.01)and the relative abundance of methanogens(P<0.05).Supplementation of GA linearly increased the molar ratio of acetate to propionate(A:P ratio)(P<0.05),but did not affect the ruminal concentrations of ammonia-N(NH3-N)and volatile fatty acids(VFA)(P>0.05).Supplementation of GA also decreased the apparent digestibility of crude protein(CP)(P<0.01).Supplementation of GA at 5.3,10.5 or 21.1 g/kg DM did not affect the N balance(P>0.05)but regulated the N excretion pattern by increasing the ratio of faecal N/urinary N and decreasing the ratio of urinary urea N/total urinary N(P<0.01)in beef cattle.Supplementation of GA tended to decrease plasma concentration of triglyceride(P ?0.080)and increase catalase(CAT)(P<0.05)in both linear and quadratic manners(P<0.05).Experiment 2 was conducted as continuous incubation(RUSITEC)and batch culture trials to investigate the effects of dietary supplementation of GA on long-and short-term in vitro rumen fermentation and CH4 production,and to test possible interactions between GA and ethanol on fermentation.The first trial was conducted using the RUSITEC as a completely randomized block design with 4 replications and 4 doses of GA:0,5,10 and 20 mg GA/g DM.Ethanol was used in all treatments to increase the solubilisation of GA in rumen fluid.The experimental period lasted 16 days,of which the first 7 days were for adaptation and the subsequent 9 days were for sampling.The second trial was a 48 h batch culture incubation conducted as a completely randomized design with a 4(GA dose;0,10,20,and 40 mg GA/g DM)× 2(with or without ethanol)arrangement of treatments.The incubation process was repeated 4 times(4 runs)and each treatment within each run had 4 replicates.In the RUSITEC trial,supplementation of GA up to 20 mg/g DM reduced CPD(P = 0.04),but did not affect CH4 production(P>0.05)expressed as mL/g DM and mL/g DMD.Supplementation of GA up to 20 mg/g DM increased butyrate,isobutyrate and isovalerate molar proportions(P<0.05)and decreased heptanoate molar proportion(P = 0.04).In the batch culture experiment,adding GA up to 40 mg/g DM linearly increased 48 h DMD,NDFD and ADFD(P<0.05)and decreased(P<0.05)CH4 expressed as mL/g DMD,mL/g NDFD and mL/g ADFD.Methane production was decreased after 24 h and 48 h only when GA was added at 10 mg/g DM without ethanol.Fermentation liquid pH and concentration of NH3-N were also reduced(P<0.05)with increasing level of GA.Treatments with ethanol notably enhanced 48 h DMD,NDFD,ADFD,GP(mL/g DM,mL/g OM or mL/g DMD),CH4 production(mL/g DM,mL/g DMD or mL/g NDFD),total VFA(TVFA)concentration,A:P ratio,acetate,valerate,isovalerate and caproate molar proportions(P<0.01)and decreased propionate,butyrate and isobutyrate molar proportions(P<0.01).Significant dose of GA × ethanol interaction was observed only for acetate molar proportion(P = 0.03).Experiment 3 included 2 in vitro batch culture study.The first one investigated the effects of condensed tannin(CT)content of leaves from four forages:Medicago sativa(alfalfa;ALF;CT-free legume),Lotus corniculatus(birdsfoot trefoil;BFT;CT-containing legume),Onobrychis viciifolia(sainfoin;SNF;CT-containing legume)and Sanguisorba minor(small burnet;SB;CT-containing forb),on nutrient disappearance,rumen fermentation,and CH4 production.Leaves were incubated with and without polyethylene glycol(PEG)to isolate the effects of CT.The batch culture study was repeated 4 times(runs)using a 4(forage sources)× 2(with and without PEG addition)factorial arrangement of treatments,with 6 replicates of each treatment.Total CT content(g/kg DM)was very low for ALF(3.3),and ranged from 18.3 for BFT,72.7 for SNF,and a high of 392 for SB.After 48 h in vitro incubations,interactions between substrate and PEG(P<0.01)occurred for all measured variables except for hydrogen gas(H2)production(P>0.05)and a tendency(P = 0.06)for protozoal numbers.Added PEG did not affect(P>0.05)dry matter disappearance(DMD)or organic matter disappearance(OMD)of ALF and BFT leaf sources,but increased(P<0.001)those of SNF by 9.7%and 9.6%,and of SB by 16.8%and 18.5%,respectively.Addition of PEG had no effect(P>0.05)on crude protein disappearance(CPD)of ALF leaf,but substantially increased(P<0.001)CPD of the other three leaf sources.For fibre components,addition of PEG did not affect(P>0.05)neutral detergent fibre disappearance(NDFD)and acid detergent fibre disappearance(ADFD)of ALF and BFT leaf sources,but increased(P<0.001)those of SNF from 44.2 to 56.5%and from 37.7 to 49.8%,and of SB from 32.6 to 66.1%and from only 8.5 to 55.8%.For gas parameters,adding PEG did not affect(P>0.05)asymptotic cumulative gas volume,rate constant of gas production(GP)or 48 h total GP of ALF and BFT,but increased(P<0.001)those of SNF and SB.The kinetics of CH4 production showed no difference for ALF leaf with and without PEG during the incubation,but addition of PEG increased CH4 production from 24 h for BFT,from 6 h for SNF and from 6 h for SB leaf sources.For fermentation variables,PEG addition lowered pH only in the case of SB(P<0.001).Addition of PEG had no effect on ammonia nitrogen concentration(P>0.05)of ALF,but substantially increased(P<0.001)that of SNF from 1.65 to 8.33 mM,that of BFT from 5.47 to 7.41 mM,and that of SB from 0.31 to 2.67 mM.Adding PEG did not affect(P>0.05)concentration of TVFA or A:P ratio(P>0.05)of ALF and BFT,but increased(P<0.001)those of SNF and SB leaf sources.The second one was investigated the effects of CT content of different proportions of ALF and SNF leaf mixtures on nutrient disappearance,rumen fermentation,and CH4 production.The batch culture study was repeated 2 times using a 5(ALF:SNF,100:0,75:25,50:50,25:75,0:100(DM basis))× 2(with and without PEG addition)factorial arrangement of treatments,with 5 replicates of each treatment.With the increment of CT content,differencs of DMD,OMD and CPD between with and without PEG increased and reducing rate of CH4 increased and then decreased as a quadratic tendency with maximum at 55.4 g/kg(CT content).Addition of PEG increased NH3-N concentration of ? 75:25,50:50,25:75 and 0:100 groups(P<0.001).Adding PEG had no effect on TVFA and A:P ratio of different forage mixture groups(P>0.05).In summary,both GA and CT are able to inhibit enteric methanogenesis and protect feed protein.Besides,dietary supplementation of GA up to 21.1 g/kg DM did not affect the N balance and the N utilisation rate,but regulated the N excretion pattern by decreasing the urinary urea excretion and the ratios of urinary N/total N excretion and urinary urea-N/total N excretion of beef cattle.There are dose-dependent and species-specific effects of CT in forage leaves on rumen fermentation.Incorporating CT-containing forages in ruminant diets may mitigate CH4 emissions and nitrogen excretion,but elevated concentrations of CT may reduce animal productivity due to lowered digestibility. |
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