The duration of time that beef cattle are fed a high-grain diet affects the recovery from a bout of ruminal acidosis: dry matter intake and ruminal fermentation.

This study was conducted to determine if the duration of time cattle are fed a high-grain diet affects their susceptibility to and recovery from ruminal acidosis. Sixteen Angus heifers (BW ± SEM, 261 ± 6.1 kg) were assigned to 1 of 4 blocks and fed a backgrounding diet consisting of 60% barley silage, 30% barley grain, and 10% supplement (DM basis). Within block, cattle were randomly assigned to 1 of 2 treatments differing in the number of days they were fed the high-grain diet before an acidosis challenge: 34 d for long adapted (LA) and 8 d for short adapted (SA). All heifers were exposed to the same 20 d dietary transition to a high-grain diet containing 9% barley silage, 81% barley grain, and 10% supplement (DM basis). Ruminal acidosis was induced by restricting feed to 50% of DMI:BW for 24 h followed by an intraruminal infusion of ground barley at 10% DMI:BW. Heifers were then given their regular diet allocation 1 h after the intraruminal infusion. Data were collected during an 8-d baseline period (BASE), on the day of the acidosis challenge (CHAL), and during 2 consecutive 8-d recovery periods (REC1 and REC2). Acidosis induction increased daily duration (531 to 1,020 min/d; P < 0.001) and area (176 to 595 (min × pH)/d; P < 0.001) that ruminal pH was <5.5 relative to BASE. Relative to BASE, inducing acidosis also increased the daily mean (0.3 to 11.4 mM; P = 0.013) and maximum (1.3 to 29.3 mM; P = 0.008) ruminal fluid lactate concentrations. There was no effect of dietary treatment on ruminal pH, lactate, or short-chain fatty acid (SCFA) concentrations (P > 0.050). However, during BASE and CHAL, SA heifers experienced greater linear (P = 0.031), quadratic (P = 0.016), and cubic (P = 0.008) coefficients for the duration of time that pH was <5.5. In addition, a treatment × day interaction for the duration that pH was <5.5 during REC1 suggested that LA cattle tended to recover from the challenge more rapidly than SA cattle (P = 0.085). Regression analysis confirmed that the LA heifers experienced a quicker linear (P = 0.019) recovery from induced acidosis over time. These results indicate adaptation of the ruminal epithelium continues with advancing time as evidenced by more stable ruminal pH both before and after an induced bout of acute ruminal acidosis but does not affect susceptibility of cattle to ruminal acidosis.