Effects of supplementation of active dried yeast and malate during sub-acute ruminal acidosis on rumen fermentation, microbial population, selected blood metabolites, and milk production in dairy cows

•Milk production and milk fat content decreased during SARA period.•Active dry yeast stabilized ruminal pH during subacute ruminal acidosis.•Malate did not significant effect on DMI, milk production, ruminal pH, total VFA, ruminal microorganism population, and selected blood metabolites. The objective of this study was to evaluate the effects of dietary supplementation of malate (MAL) and active dried yeast (ADY) on feed intake, rumen fermentation parameters, rumen microbial populations, selected blood metabolites, and milk production during a sub-acute ruminal acidosis (SARA) challenge in primiparous lactating dairy cows. Six rumen-fistulated Holstein dairy cows (body weight: 630±55kg, 110±25 days in milk, mean±SD) were assigned to the following treatments in a 3×3 Latin square design: (1) control TMR (CON); (2) a TMR supplemented with 80g of sodium–calcium malate/head per day (MAL); and (3) a TMR supplemented with 10g of active dried yeast providing 20×109 CFU of Saccharomyces cerevisiae/head per day (ADY). Each experimental period consisted of 14 days of adaptation to the experimental treatments, 4 days of SARA challenge, and 10 days of rest. Dry matter intake (18.4 vs. 19.8kg/day), and milk yield (29.3 vs. 30.4kg/day) were depressed during SARA compared with adaptation. Malate and ADY had no effect on DMI and milk yield during the adaptation and SARA phases. Malate and ADY had no effect on ruminal pH characteristics during adaptation. During SARA, maximum and mean ruminal pH was not affected by supplementation, but minimum ruminal pH tended to be higher for ADY compared to CON and MAL. Time spent with ruminal pH