Relationships between dry matter intake and acid-base status of lactating dairy cows as manipulated by dietary cation-anion difference

Our objective was to examine potential relationships between dry matter intake (DMI) and acid-base status of lactating dairy cows as manipulated by dietary cation-anion difference [DCAD: defined as milliequivalents of Na + K - Cl per 100 g of feed dry matter (DM)]. A database was developed from 16 studies of DCAD effects on DMI and production of lactating dairy cows in which 21 experiments, including 88 dietary treatments (DCAD ranging from -19.1 to 72.7) and 337 cows, occurred. Observed DMI values were adjusted for study effects. Adjusted DMI increased quadratically with increasing DCAD (P < 0.001; R-2 =0.76), peaking at 47 meq/100 g of DM. Adjusted DMI also increased as blood HCO3- concentrations (quadratic, P < 0.001; R-2 = 0.83), blood pH (linear, P < 0.001; R-2 = 0.82) and urinary pH (quadratic, P=0.009; R-2 = 0.66) increased. Adjusted DMI peaked at blood HCO3- concentration of 30.3 meq/l, or urinary pH of 7.87. These relationships between adjusted DMI and blood HCO3-, blood pH and urinary pH suggest that DMI is closely associated with acid-base status of lactating dairy cows, and that DCAD affects systemic acid-base physiology which, in turn, affects voluntary intake of lactating dairy cows. (c) 2006 Elsevier B.V. All rights reserved.