Evaluation of the protective effect of probiotics fed to dairy cows during a subacute ruminal acidosis challenge

Subacute ruminal acidosis (SARA) can be extremely costly when it occurs in dairy cows. The use of probiotic supplements to stabilize rumen pH during the transition period following parturition could attenuate the symptoms of this metabolic disorder. Four ruminally fistulated Holstein dairy cows in mid to late lactation were assigned to the following experimental treatments in a 4 × 4 Latin square design: (1) control (C); (2) 0.6 g/cow/d of a fermentation extract of Aspergillus oryzae (AO-0.6); (3) 3 g/cow/d of A. oryzae (AO-3.0); and (4) 2 g/cow/d of a probiotic combination consisting of Enterococcus faecium and Saccharomyces cerevisiae (ES). Each period of the Latin square consisted of three weeks of adaptation to the respective treatments followed by four days of induction of SARA and three days of rest. During the four days of induction of SARA, 0.30 of ad libitum intake of the total mixed ration (TMR) was replaced with wheat and barley pellets (WBP) containing 0.5 ground wheat and 0.5 ground barley. Ruminal pH was recorded continuously using an indwelling pH probe over a 24 h period for each week of the adaptation period and continuously over the four days of SARA induction. Average ruminal pH was lower (P=0.0001) during SARA than during the weeks of adaptation (5.6 versus 6.1). When the cows were fed ES, the minimum pH recorded was higher (P=0.05) (5.0) than when they were in the control (4.4). The proportion of time during which pH was between 5.6 and 6.0 was higher (P=0.05) with ES (0.31) than with C (0.22). Mean pH tended (P=0.06) to be higher with ES (5.84) than with C (5.41), and the proportion of time during which pH was below 5.2 tended (P=0.09) to be lower with ES (0.09) than with C (0.31). AO-0.6 tended (P=0.07) to increase minimum pH (4.96) compared with C (4.43) and tended (P=0.08) to decrease the percentage of time during which pH was below 5.2 (0.08 versus 0.31 for AO-0.6 and C, respectively). The addition of probiotics during SARA had no effect on the number of cellulolytic bacteria or on the population of Megasphaera elsdenii in the rumen.