Evaluation of diagnostic measures for subacute ruminal acidosis in dairy cows

Li, S., Gozho, G. N., Gakhar, N., Khafipour, E., Krause, D. O. and Plaizier, J. C. 2012. Evaluation of diagnostic measures for subacute ruminal acidosis in dairy cows. Can J. Anim. Sci. 92: 353–364. Effects of subacute ruminal acidosis (SARA) challenges on measurements of feces, urine, milk and blood samples, and of feeding behavior were investigated to determine which of these measurements may aid in the diagnosis of SARA. Eight multiparous lactating dairy cows were used in a crossover design with two 6-wk experimental periods. During weeks 1, 2, and 6, cows received a control diet with a forage-to-concentrate ratio of 58:42. During weeks 3 to wk 5, a grain-based SARA challenge (GBSC) or an alfalfa-pellet SARA challenge (APSC) was conducted by replacing 12% of the dry matter of the control ration with pellets containing 50% ground wheat and 50% ground barley, and by replacing 26% of the dry matter of the control ration with pellets of ground alfalfa, respectively. The rumen pH depression did not differ between the challenges. The GBSC increased the concentrations of lipopolysaccharide (LPS) in feces and of serum amyloid A in blood, but decreased that of milk fat and urea in blood. The APSC increased the urine pH, the net-acid-base excretion, and the red blood cell count and potassium concentration in blood. Both challenges increased the concentrations of LPS and propionate in rumen fluid, protein in milk, glucose, lactate and sodium and the partial pressure of CO₂ in blood, and tended to decrease the concentration of chloride in blood. The measures that were similarly affected by both challenges may aid in the diagnosis of a rumen pH depression. Differences between the SARA challenges suggest that this disorder is not solely rumen pH dependent.