Effect of acidosis in the late-finishing phase on rumen fermentation in feedlot steers

Abstract

Abstract The objective was to determine the effects of induced acidosis in the late-finishing phase on rumen fermentation in feedlot steers. Eleven ruminally cannulated steers (body weight = 795 kg ± 54) were blocked into 2 groups based on initial body weight. For 195 d prior to the start of the study, cattle were consuming a basal finishing diet (60% dry rolled corn, 15% modified distillers grains, 15% corn silage, and 10% ground corn-based supplement). Steers were randomly assigned to 1 of 2 treatments: control (CON), or induced acidosis (ACD). Both treatments were fasted for 24 h then fed the basal finishing diet. Steers on the ACD treatment received 0.05% of BW of wheat starch via rumen cannula at 0800 h and 2000 h on d 1 and ad libitum refeeding following the fast. On d 1 and 2, CON steers were provided 25% of allotted feed every 6 hours. Rumen fluid was collected every 4 h during the challenge period (h 0 – 48), and 0, 6, and 12 h after feeding during the recovery period (h 54 – 96). Rumen fluid was analyzed for pH, ammonia, volatile fatty acids (VFA), and lactate. Fecal grab samples were collected every 8 h to determine fecal pH. A treatment × day interaction (P = 0.03) was observed for dry matter intake during the challenge period with steers on the ACD treatments consuming more on d 1 than CON steers. Intake was not different on d 2 (P = 0.88). A treatment × hour effect (P < 0.01) was observed for ruminal pH during the challenge period with the ACD steers having a lesser pH than CON from h 12 to 32. Duration of time below a pH of 5.6 during the challenge period was greater (P < 0.01) for ACD steers than CON. During the challenge period, a treatment × time interaction (P = 0.04) was observed for total VFA concentration with ACD steers having greater total VFA concentration from h 12 to 36. Acetate to propionate ratio (A:P) was affected by treatment × hour (P = 0.04) with CON steers having greater A:P from h 28 to 48. Rumen ammonia and lactate concentrations did not differ (P ≥ 0.25) between treatment or the interaction with time. Challenge and recovery period fecal pH were not affected (P ≥ 0.13) by treatment, time, or their interaction. Recovery period ruminal pH was not different (P = 0.99) between treatments. For the recovery period, total VFA and ammonia concentration were not affected by treatment, time, or their interaction (P ≥ 0.07). Ruminal pH and VFA were affected in the initial 48 h of induced acidosis in the late-finishing phase.