Evaluation of models of acute and subacute acidosis on dry matter intake, ruminal fermentation, blood chemistry, and endocrine profiles of beef steers

Crossbred steers (n = 20 316 +/- 4 kg BW), each fitted with a ruminal cannu la, were used to evaluate the effects of acute acidosis (AA) and subacute a cidosis (SA) on DMI, ruminal fermentation, blood chemistry, and endocrine p rofiles. Animals were blocked by BW and assigned to treatments including 1) intraruminal (via cannula) steam-flaked corn (3% of BW; AA); 2) intrarumin al dry-rolled wheat:dry-rolled corn (50:50; 1.5% ofBW; SA); 3) offering for age-adapted steers ad libitum access to a 50% concentrate diet (AA control; AC); and 4) offering 50% concentrate diet-adapted steers ad libitum access to a 50% concentrate diet (SA control; SC). Samples of ruminal fluid and w hole blood were collected on the day of the challenge (d 0) and 3, 7, 10, a nd 14 d after the challenge. Daily DMI responded quadratically (P < 0.01) t hrough d 7 for AA and SA steers and increased linearly (P < 0.01) for AC st eers. Dry matter intake by AA steers reached a nadir (< 3 kg/d) on d 3 and gradually increased to a level similar to other treatments (7 kg/d) by d 10 , whereas DMI by SA steers increased through d 3. Blood pH, bicarbonate, ba se excess, and total CO2 were decreased (P < 0.03) for AA. steers and incre ased (P < 0.03) for SC steers through d 7. Ruminal pH decreased quadratical ly (P < 0.01) in AA and AC steers and increased (P = 0.01) in SA steers thr ough d 7. Ruminal total lactate concentration and osmolality responded quad ratically (P < 0.01) for AA and AC steers. Ruminal total lactate peaked on d 3 for AA steers and on d 0 for AC and decreased to basal concentrations b y d 7. Plasma NEFA concentration increased (P < 0.04) on d 3 and 7 for AA s teers. Serum Na decreased (P < 0.05) on d 0 for AA and SA steers and on d 7 and 14 for AA steers. Serum P decreased (P = 0.01) for AA steers through d 7 and decreased quadratically (P = 0.01) for AC steers through d 7. Serum albumin and cholesterol decreased (P < 0.02) for AA and AC steers through d 7. Area under the GH curve decreased (P = 0.02) for AA and AC steers throu gh d 7. Considerable variation was evident in the ability of an animal to c ope with a carbohydrate challenge. Results of data modeling generally sugge st that serum amylase activity, cholesterol and potassium concentrations, a nd plasma NEFA concentrations were useful in distinguishing between steers classified as experiencing subacute acidosis or not affected by a carbohydr ate challenge.