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; R2 = 0.76), peaking at 47 meq/100 g of DM. Adjusted DMI also increased as blood HCO3− concentrations (quadratic, P<0.001; R2 = 0.83), blood pH (linear, P<0.001; R2 = 0.82) and urinary pH (quadratic, P=0.009; R2 = 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.