Addition of sodium bicarbonate to rations of postpartum dairy cows: physiological and metabolic effects

Sodium bicarbonate was added to complete mixed rations to characterize physiological, metabolic, and ruminal changes immediately postpartum when dairy cows are switched abruptly from a low energy ration prepartum to a high energy ration postpartum. Twelve Holstein cows were paired and assigned randomly to either a control or buffered ration containing .8% sodium bicarbonate. Rations consisted of 50% corn silage:50% concentrate. All All cows were fed a similar dry cow ration for a minimum of 7 days prepartum and experimental rations for 2 wk beginning at parturition. Blood, feces, and urine were sampled on days 1, 2, 4, 7, 10, and 14 postpartum. Rumen fluid was sampled on days 7 and 14. Dry matter intake and milk production were 2.75% of body weight and 30.3 kg/day for cows fed buffer and 2.49% and 27.6 kg/day for cows fed control. Higher partial pressure of carbon dioxide and base excess in blood in cows fed buffer existed on days 2 and 4 postpartum than for cows fed the control ration. Cows fed buffer had higher concentrations of ruminal ammonia than cows fed control. This difference was less pronounced in blood urea nitrogen and urinary ammonia. Urine pH was higher for cows fed buffer than for control. Addition of sodium bicarbonate improved the acid-base status after abrupt change of ration and may be associated with increased dry matter intake and improved ration adaptation. Concentrations of most minerals and metabolites in blood serum did not differ between rations.