The objective of this study was to investigate whether it is possible to create acute laminitis in young ruminating calves by feeding high carbohydrate diets. Three experiments were performed. In the first, 16 calves, 17 wk of age, were fed one of four diets (4 replications) that contained either 71 or 81% of TDN and either 15 or 20% CP. Jugular blood and rumen fluid were sampled and hoof temperature measured at frequent intervals over a subsequent 2-d period. Calves responded acutely to the 81% TDN diets by anorexia, stiffness and diarrhea. Ruminal pH was lower and L- and D-lactates greater in the rumen of 81% TDN treatments. Total ruminal VFA decreased as pH declined. Proportion of acetate increased while propionate decreased in 81% TDN treatments. Butyrate differed but was not dietary related. Whole blood L-lactate did not differ by treatments. Blood D-lactate increased significantly in the calves fed 81% TDN, peaking at 32 h (65 mg/dL). Hoof temperature was significantly lower in 81% TDN treatments at 28-32 h. In the second experiment dietary sodium bicarbonate (.9% of DM) attenuated lactic acidosis in animals which consumed high quantities of concentrate. Although some animals in the buffer group suffered from acidosis, sickness was potentiated in nonbuffer group. Buffer inhibited the decline of ruminal fluid pH, and the increase of lactate in the rumen. Total VFA in the rumen declined with pH. Proportions of major VFA remained unchanged. Blood L-lactate increased at 28 h in animals which did not receive buffer. Blood D-lactate increased in both treatments and was greater in nonbuffer treatment. In the third experiment, 24 calves, 17 wk of age, were fed diets containing either 68 or 80% TDN. The latter diet was supplemented with either ionophore, buffer or contained no supplementation. Sudden introduction of the diets resulted in transient lactic acidosis. Buffer was more efficient in the prevention of acidosis than ionophore. The acetate : propionate (Ac:Pr) ratio tended to be lower in ionophore treatment. Growth performance did not differ between the treatments. Acute laminitis was not detected but the reduction of ruminal pH and a many fold increase in blood D-lactate observed in this study, may contribute to occurrence of laminitis. / Ph. D.