| Purple prairie clover(PPC,Dalea purpurea Vent.)is a native legume that has been shown to possess high nutritional value and good palatability.Previous studies also found that PPC contained a unique array of naturally occurring compound-condensed tannin(CT)that possess varying bioactivity including antimicrobial activity.However,little information is available regarding the effects of feed preservation and processing methods on the efficacy of CT affecting its nutritional quality and biological activity.The objectives of the present studies conducted in this thesis were 1)to determine the structural composition,protein precipitation and anti-Escherichia coli properties of CT from PPC conserved as freeze-dried(FD,representing green chop),silage(SIL)and sun-cured hay(HAY);2)to assess effects of conservation method on in vitro ruminal fermentation of PPC in batch culture;3)to evaluate effects of CT on bacterial and fungal core microbial community involved in ensiling and aerobic exposure of PPC silage;4)to evaluate effects of PPC preserved as hay and its CT on growth performance,wool growth,nutrient digestibility,blood metabolites and ruminal fermentation in lambs fed total mixed rations.The main results are as follows:1.Conservation method had no effect on concentration of total CT,but ensiling decreased(P<0.001)extractable CT and increased(P<0.001)fibre-bound and protein-bound CT.In contrast,hay-making increased(P<0.01)protein-bound CT only.Regardless conservation method,the predominantly structural composition of PPC CT was procyanidin(PC)and epicatechin(EC).The SIL CT had lowest(P<0.001)epigallocatechin(EGC)but highest(P<0.01)EC in the extension units.Similarly,CT in SIL exhibited lower(P<0.001)mean degree of polymerization(mPD),but higher(P<0.001)PC/PD(prodelphinidin)than that in FD or HAY.The protein-precipitating capacity of CT in the conserved PPC ranked(P<0.001)in the order of FD>HAY>SIL.Growth of E.coli in M9 medium was inhibited by 25～100 μg/mL of CT isolated from FD,SIL and HAY(P<0.05),but preservation method had no effect on the efficacy of CT in inhibiting the bacterial growth.The results demonstrated that ensiling decreased the extractability of CT and decreased protein-precipitating capacity of the extractable CT by reducing PC/PD ratio.Purple prairie clover conserved as hay conserved the biological activity of CT via preserving extractable CT more than as silage.2.The FD had higher(P<0.001)content of water soluble carbohydrates(WSC)but lower(P<0.01)concentrations of NDF and ADF than that of HAY and SIL.Total gas and methane production(in mL/g NDFD)and NDF digestibility(NDFD)were higher(P<0.01～0.001)in FD as compared to that of HAY and SIL,whereas inclusion of polyethylene glucol(PEG)that specifically inactivate CT did not affect true DM digestibility(TDMD)or NDFD at 8,24 or 72 h of incubation.Incubation with HAY produced lower(P<0.05～0.001)content of total VFA and microbial N than that of incubation with FD or SIL,whereas incubation with SIL had higher(P<0.001)concentration of NH3-N than that of FD and HAY.Addition of PEG increased(P<0.001)ammonia accumulation but decreased(P<0.05～0.001)microbial N during 72-h incubation.The results demonstrated that CT in PPC had minimal effect on rumen fermentation,and conservation of hay and silage had little effect on the efficacy of CT in modulating rumen fermentation.3.Condensed tannins decreased(P<0.05～0.001)soluble N,non-protein N,ammonia N,deoxynivalenol(DON)and ochratoxin A(OTA)content as well as the magnitude of the temperature increase during ensiling and aerobic exposure of PPC silage.Real-time PCR analysis revealed that gene copy numbers of total bacteria,Lactobacillus,yeasts and fungal increased(P<0.001)except for Lactobacillus after 14-d aerobic exposure.Diversity measurements of bacterial and fungal communities indicated that CT increased(P<0.01)bacterial diversity during ensiling and aerobic exposure,whereas it increased(P<0.05)fungal diversity only during aerobic exposure.Condensed tannins improved fermentation quality and aerobic stability of silage by decreasing protein degradation and inhibiting growth of majority bacteria,fungus and yeast,especially those undesired or mycotoxin producing microorganisms.4.Lambs fed PH had lower(P<0.01)DM intake than AH or PH-p.Growth performance,carcass characteristics and wool growth parameters did not differ among diets.Lambs fed PH-p had greater(P<0.05～0.001)DM,OM,CP,NDF and ADF digestibility than those fed AH,and greater(P<0.05～0.001)CP,NDF and ADF digestibility than those fed PH diet Lambs consuming PH diet had lower(P<0.05)blood urea nitrogen and creatinine than AH and lower(P<0.05)blood glucose and urea than PH-p,but greater(P<0.01)total antioxidant capacity and catalase activity than AH diet.Lambs fed PPC CT had lower(P<0.05)concentrations of ammonia,total VFA,propionate,iso-butyrate,iso-valerate and protozoa.Overall,CT in PPC possess strong protein-precipitating capacity and anti-microbial activities,inhibiting protein degradation with improving the fermentation quality and aerobic stability of silage and benefiting for immunity and animal health.This study provides a scientific basis for the theoretically reaearch of CT and application of PPC in the field of animal feed by providing CT’s structural information of PPC which conserved as freeze-dried,silage and hay,obtaining the basic principles of effects of CT on protein precipitation and anti-E.coli properties as well as characteristics of in vitro ruminal fermentation,studying impact mechanism of CT on bacterial and fungal core microbial community involved in the ensiling and aerobic spoilage of PPC silage as well as assessing nutritional value and feeding value of PPC hay. |
