Factors related to variation in the susceptibility to subacute ruminal acidosis in early lactating Simmental cows fed the same grain-rich diet

Abstract Cow variation in the ruminal pH responses to high-grain feeding has been noted but the factors responsible for susceptibility are inconclusive. The present study investigated a broad spectrum of responses including feed intake, performance, ruminal pH and temperature, chewing activity, feed sorting, blood metabolic variables, and acute phase response (APR) of early lactating cows. Eighteen lactating Simmental cows (initial DIM = 66.6 ± 20.45; BW = 712 ± 101.3 kg; milk yield = 28.7 ± 7.0 kg, mean ± SD) were balanced by parity and DIM and randomly assigned to 2 feeding regimens: control (n = 6) and SARA diet (n = 12). The feeding trial lasted 36 d consisting of a 1-week baseline and a 4-week experimental period. All cows started at baseline being fed a 40% concentrate diet. Afterward, the control cows continued with the 40% concentrate diet for the next 29 d, whereas the SARA cows were fed a 60% concentrate diet in the first (SARA1), third (SARA2) and last week (SARA3) of the feeding trial. In the second week, they were fed the control diet. Based on the area of reticular pH below 6.0, the SARA cows were further divided into susceptible and tolerant groups (n = 6 each). Compared with tolerant, the susceptible cows had a longer duration of reticular pH