Calcium homeostasis, acid-base balance, and health status in periparturient Holstein cows fed diets with low cation-anion difference

Forty multiparous Holstein dry cows on d 21 prepartum were randomly allocated to four blocks of 10 cows to examine the effects of reducing the dietary cation-anion difference (DCAD) on calcium homeostasis, acid-base balance, health status, and subsequent lactation performance. The reduced DCADs (Na+K-Cl-S, mEq/kg DM) of +150,+50, -50, and -150 were obtained by addition of anionic salts. Reducing DCAD resulted in mild metabolic acidosis as indicated by the sharp decline in urinary pH, and minor reductions in blood pH and HCO3- concentration. Greater plasma calcium concentration was observed in cows fed diets of -50 and -150 DCAD (P<0.05) than those on +50 and +150 DCAD diets. The nadir of plasma calcium level on the day of calving was lower (P<0.05) than the highest level on d 14 prepartum (8.33 vs. 9.30 mg/dL). Composite colostrum calcium concentration was decreased (P<0.05) with time on d I relative to d 2 postpartum (0.212 vs. 0.174%), and feeding of diet - 150 DCAD induced higher (P<0.05) composite colostrum calcium content than other three DCAD diets. No case of milk fever occurred for any diets, but feeding the two negative DCAD diets reduced (P<0.05) retained placenta incidence compared with diet of + 150 DCAD. Dry matter intake, milk yield and compositions of fat, protein, and lactose were non-significantly affected (P>0.05) by dietary treatments. In conclusion, urinary pH is an effective indicator of extracellular fluid acid-base balance, and feeding negative DCAD in late gestation period is beneficial for dairy cows in blood calcium homeostasis and improvement of health status. (C) 2007 Elsevier B.V. All rights reserved.