Statistical evaluation of early- and mid-lactation dairy cow responses to dietary sodium bicarbonate addition

Our objectives were to examine, using mixed model statistical analysis, effects of dietary NaHCO3 on performance of early- and mid-lactation dairy cows and to determine if there is an optimal level of dietary buffer addition. A database was developed from 27 studies published between 1980 and 1999 that included a total of 30 experiments, 73 dietary treatments and 369 cows. Dietary NaHCO3 was categorized according to amount in the diet as control (0.0 g/kg), moderate (7.0-10.0 g/kg), or high (10.5-15.0 g/kg) with NaHCO3 concentrations outside these ranges not included. Forage type in the rations was categorized as maize silage (MS), when it was the sole or main dietary forage, or as forage other than MS (NMS) when alfalfa hay, or silages based on alfalfa, barley, sorghum, triticale, or wheat were the sole or main dietary forages. The statistical model included the fixed effects of buffer concentration and forage type, and the random effect of study. Dry matter (DM) intake (DMI) did not differ among buffer treatments for cows fed NMS, but cows fed MS without NaHCO3 addition consumed 1.24 kg/d less DM (P < 0.02) than cows fed buffer. The DMI did not differ between moderate and high dietary NaHCO3 feeding levels in cows fed MS. Milk production, milk protein proportion, and protein yield were unaffected by buffer treatments regardless of forage type, but milk fat proportion of cows fed MS based diets was 2.7 g/kg higher (P < 0.02) when NaHCO3 was included. Addition of NaHCO3 at 7.0-10.0 g/kg of dietary DM was optimal for early- and mid-lactation cows fed MS based diets, but addition of NaHCO3 to NMS based diet was not supported. However, forage type was confounded with acid detergent fibre content of the diet, differences in response to buffer treatments between forage type might be partially because of variation in the fibre contents of the forage.