Impact of subacute ruminal acidosis on health of dairy cows

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Subacute ruminal acidosis (SARA) is a common metabolic disease of dairy cows during which the rumen pH is depressed for several hours daily. The mechanisms responsible for the symptoms of this disease are not fully understood. This hinders the diagnosis, prevention, and treatment of SARA. Research conducted during my previous NSERC Discovery Grant provided new insights into the etiology of SARA, but also brought up new questions about this etiology. My research showed that SARA challenges conducted by feeding high-grain diets were associated with increased bacterial lipopolysaccharide endotoxins (LPS) in rumen fluid, in digesta in the large intestine, and in peripheral blood, and with inflammation. SARA challenges conducted by feeding diets containing pellets of ground alfalfa were also associated with increased LPS in the rumen, but were not associated with increased LPS in the large intestine and in peripheral blood, and with inflammation. I believe that the differences between these SARA challenges were due to the comparatively higher dietary starch content during grain-based SARA challenges. I hypothesize that, in contrast to alfalfa-pellet SARA challenges, grain-based SARA challenges increase the acidity and LPS content of digesta in the large intestine, and that this causes translocation of LPS and, subsequently, systemic inflammation. Using my new NSERC Discovery Grant, I will answer to following questions to test my hypotheses by conducting in vivo experiments with cattle: 1. Do SARA challenges affect the morphology of the epithelia of the digestive tract in a manner that enables translocation of LPS and causes systemic inflammation?; 2. Where do translocations during SARA challenges occur?; 3. Does the starch content of digesta in the large intestine affect LPS and barrier function in the large intestine?; 4. Is the inflammation observed during SARA challenges related to translocation of LPS? The grant will also be used to train at least 1 Ph.D, 1 M.Sc., and 5 undergraduate students. This research will provide critical insights in the etiology of SARA, but also on the effects of nutritional challenges on the barrier function of the digestive tract and on fermentation in the large intestine in cattle.