Characterization Of Condensed Tannins In Purple Prairie Clover And Determination Of Its Effects On Digestive Characteristics Of Lambs

Condensed tannins（CT） are phenolic compounds that widely present in plant regime including legume forages. Condensed tannins from different sources have been shown to possess varying biological activities. Purple prairie clover（PPC; Dalea purpurea Vent.） has been shown to contain high concentrations of CT that exhibits strong anti-Escherichia coli and antiEscherichia coli O157:H7 activity in vitro and in vivo, which is not observed in other common forages. Therefore, feeding PPC to ruminants offers promise for dietary mitigation of E. coli O157:H7 in ruminant production thereby increase the animal product safty which is paramount to human health. There is great need to elucidate the chemical characteristics of PPC CT in order to understand its antimicrobial mechanisms as well as to determine its effect on digestion process. The objectives of studies conducted in this thesis were 1) to determine the chemical structure and phenolic compound compositions of PPC CT, and its relationship to biological activity; 2) to determine the ruminal and intestinal digestion of PPC conserved as hay and silage; 3) to determine the effects of CT on nutrient digestion and on fecal shedding of E. coli O157:H7 in sheep fed PPC; and 4) to determine the effect of CT on intestinal microbial composition of sheep fed PPC.1. The contents and chemical structure of PPC CT varied with different plant tissues and growth periods. Flower contained the highest content of CT while stem contained the least throughout the whole growth period.The contents of CT decreased with plants mature.PPC CT were predominantly of the procyanidin-type, with epicatechin as the main unit and epigallocatechin making up the rest. Compared to stem and flower, leaf CT contained higher proportion of procyanidin-type subunits with more epicatechin and less epigallocatechin.The mDP of PPC CT was highest in stem and lowest in leaf.The content of CT decreased whereas the mDP increased in the mature stem. CT from PPC leaf had higher protein-precipitating capacity than stem and flower, while leaf CT in early flower period showed the highest protein-precipitating capacity, which could be attributed to their chemical structures.2. Both ensiling and sun-curing did not affect total CT content in PPC, but significantly increased the level of bound CT in PPC. Compared to freeze-dried forage, both PPC hay and silage reduced in situ ruminal degradation, but not in vitro simulated intestinal digestion of DM. However, preserving PPC as hay decreased ruminal degradation of CP and NDF, but increased intestinal digestion of CP. In contrast, preservation as silage increased ruminal degradation of CP and NDF, but decreased intestinal digestion of CP.3. Feeding alfalfa-PPC mixtures to lambs(CT content 36 g kg^-1 DM) did not affect feed intake or digestibility of OM or NDF, but reduced CP digestibility in lambs. Feeding alfalfa-PPC mixtures to lambs significantly reduced feacal shedding of E. coli O157:H7, enhanced serum antioxidant capacity and afftected some serum metabolites but had no effect on animal health as compared to feeding alfalfa alone. These activities in PPC were attributed to both CT and non-CT phenolics in PPC.4. The fecal microbiota of lambs in the first experiment were investigated by 16 S rRNA gene pyrosequencing technology. The results showed that PPC CT up to 36 g kg^-1 DM in the diet exerts minor effect on the overall fecal microbial community of lambs although alterations were noticeable in several specific taxa.The results demonstrated that PPC is a promising forage for improving protein utilistion and animal health and developing a pre-harvest strategy to enhance the safety of ruminant products.