Probiotic and dietary manipulation of the gastrointestinal tract microbiota in beef cattle: towards improved performance under different dietary management in Canadian Prairies
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Microbial symbionts inhabiting the digestive tract of ruminants contribute to a wide range of metabolic functions essential for the survival of host. However, abrupt changes in the composition of diet can adversely affect the composition of these microbial communities, leading to metabolic disorders that could compromise the performance of the animals. Development of frothy bloat following exposure of over-wintered steers to legume pastures and impairment of ruminal fermentation as a result of feeding high-grain diets are common metabolic disorders affecting beef cattle in Canadian Prairies. Mitigation strategies to control these metabolic conditions are mainly based on dietary interventions, providing moderate protection to cattle. Understanding the contribution of microbiota to development of these metabolic conditions would pave the way towards implementing more effective strategies. In the first experiment of this thesis, the effects of supplementing the probiotic strain Propionibacterium acidipropionici P169 on the microbiota and metabolic profile of feedlot cattle receiving a high-grain diet were evaluated. Overall, the data suggest that P169 confers its beneficial effect via favoring the growth of cellulolytic bacteria, thus inhibiting the overgrowth of amylolytic bacteria and subsequent drop in the ruminal pH. In the second experiment, dynamics of rumen microbiota during development of frothy bloat and following administration of mitigating strategies was characterized (i.e., use of mixed alfalfa and sainfoin pasture and supplementing drinking water with Alfasure™). The data suggest that rapid proliferation of amylolytic bacteria following consumption of alfalfa contribute to development of frothy bloat. Dietary interventions used in this study prevented the development of clinal bloat, increased the proportions of cellulolytic bacteria, and alleviated bloat-associated dysbiosis in the composition of rumen microbiota. Finally, the third study evaluated the interrelationships of anaerobic rumen fungi (ARF) and ruminal bacteria in the context of frothy bloat. In general, ARF showed a large number of negative interrelationships with ruminal bacteria in normal rumen conditions. However, development of frothy bloat decreased the total number of relationships between ARF and bacteria, implying a disruption of microbe-microbe interrelationships (i.e., dysbiosis). Collectively, this thesis provides novel insights into the contribution of rumen microbiota to common metabolic disorders of beef cattle.