Effects of a Megasphaera elsdenii oral drench on reticulorumen pH dynamics in lactating dairy cows under subacute ruminal acidosis challenge

Subacute ruminal acidosis (SARA) is an important disorder in dairy cattle with economic and animal welfare implications. A preventive strategy for SARA control is oral drenching of probiotics, such as Megasphaera elsdenii. The aim of this study was to evaluate the effects of a M. elsdenii oral drench on reticulorumen pH, milk yield and components, and feeding behavior of lactating cows under a SARA challenge. This study consisted of two crossover trials with 8 cows each to determine the efficacy of drenching live culture of M. elsdenii NCIMB 41125. Experimental period of each trial lasted 8 d with a 4 wk washout interval between periods. The first 3 d of each period were considered baseline days. On day 4 of the period, feed delivered was reduced by half, based upon individual mean dry matter intake (DMI) during the baseline period. On day 5 of the period, all cows received a challenge diet rich in highly fermentable carbohydrates offered to the cows for 2 h to induce SARA. Orts were weighed and replaced with regular diet offered ad libitum. The last 3 d of each experimental period were considered recovery days. The difference between each trial was the administration time of M. elsdenii drench, where in Trial 1 it was delivered 4 d before (PRO_-4) and in Trial 2 it was delivered the day before (PRO_-1) the SARA challenge. Cows were randomly assigned to either a treatment (PRO_-4 or PRO_-1) or control (CON_-4 or CON_-1) drench, and reversed on the subsequent period. During Trial 1, PRO_-4 cows produced more milk (P < 0.01), with greater protein percentage (P = 0.03) and lesser fat to protein ratio (P = 0.01) compared with control cows. PRO_-4 cows also had greater overall reticulorumen pH and experienced shorter and less intense acidosis (P < 0.05) and greater DMI (P = 0.04) compared with control cows. Feeding behavior was not affected by treatment in Trial 1 (P > 0.10). In Trial 2, only feeding time was affected by the treatment, with PRO_-1 cows spending more minutes per day feeding (P < 0.01) compared to control cows. The results indicate potential benefits of a M. elsdenii drench on rumen pH dynamics, acidosis resilience, and possibly milk production and feed intake. However, it appears that the time of drench administration might influence M. elsdenii establishment and drench efficacy.