The objective was to determine if reduction in DMI by diets with negative DCAD is mediated by inclusion of acidogenic products (AP), content of Cl, or by changes in acid-base (AB) status. The hypothesis was that the decrease in DMI is mediated by metabolic acidosis and not by feeding AP. Ten nulliparous Holstein cows at 148 ± 8 d of gestation were enrolled in a duplicated 5 × 5 Latin square design. The DCAD of diets and AB status were manipulated by incorporating an AP or adding salts containing Cl, Na, and/or K to the diets. Treatments were a base diet (BD) containing 55% corn silage, 10% grass hay, and 35% concentrate, without any added AP or salts (T1; K = 1.42%, Na = 0.04%, Cl = 0.26%; DCAD = 196 mEq/kg); the BD with added 1% NaCl and 1% KCl (T2; K = 1.83%, Na = 0.42%, Cl = 1.23%; DCAD = 194 mEq/kg); the BD with added 7.5% AP and 1.5% NaHCO₃ and 1% K₂CO₃ (T3; K = 1.71%, Na = 0.54%, Cl = 0.89%; DCAD = 192 mEq/kg); the BD with added 7.5% AP (T4; K = 1.29%, Na = 0.13%, Cl = 0.91%; DCAD = −114 mEq/kg); and the BD with 7.5% AP, 1% NaCl, and 1% KCl (T5; K = 1.78%, Na = 0.53%, Cl = 2.03%, DCAD = −113 mEq/kg). Periods lasted 14 d with the last 7 d used for data collection. Data were analyzed by the MIXED procedure of SAS for a replicated Latin square design. Feeding behavior was evaluated for 12 h/d in the last 2 d of each period. Contrasts evaluated included the effects of AP (AP: T1 vs. T4), AB status (AB:T2+T3 vs. T4+T5), and addition of Cl salts to an alkalogenic diet (ClAlk: T1 vs. T2) or to an acidogenic diet (ClAc: T4 vs. T5). Feeding acidogenic diets induced a compensated metabolic acidosis and reduced DMI but correcting the metabolic acidosis reestablished DMI in dry cows. The decrease in DMI in diets with negative DCAD was mediated by metabolic acidosis and not by addition of AP or Cl salts. Table 1.

Item	T1	T2	T3	T4	T5	SE
DMI, kg/d*§	10.3	10.2	10.2	9.7	9.5	0.2
DMI, % of BW*§	1.76	1.75	1.74	1.68	1.64	0.03
Urine pH*§‡	8.1	7.9	7.9	5.7	5.6	0.06
Blood pH*§‡	7.450	7.436	7.435	7.420	7.416	0.005
Blood HCO3-, mM*§	25.9	25.5	25.8	24.3	23.7	0.3
Eating bouts, n/12h*§	6.8	6.3	7.1	5.8	6.1	0.4
Intermeal interval, min*§	90.8	99.3	84.7	111.5	104.0	6.8

*AP (P < 0.05); ^§AB (P < 0.05); ^‡ClAlk (P < 0.05); ^†ClAc (P < 0.05).