LAUSR

Abstract 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   0.10). In Trial 2, only feeding time was affected by the treatment, with PRO-1 cows spending more minutes per day feeding (P