Recovery of absorptive function of the reticulo-rumen and total tract barrier function in beef cattle after short-term feed restriction

Our objective was to determine if the severity of short-term feed restriction (FR) affects the timeline for recovery of the absorptive function of the reticulo-rumen and barrier function of the total gastrointestinal tract in beef cattle. Eighteen ruminally cannulated and ovariectomized Angus x Hereford heifers were housed in individual pens. Heifers were blocked by initial BW into 3 blocks and, within block, randomly assigned to 1 of 3 treatments that differed in the severity of FR: heifers were restricted to 75, 50, or 25% of ad libitum intake. Treatments were imposed during a 5-d period of FR followed by 3 consecutive wk of recovery (REC1, REC2, and REC3). Throughout the experiment heifers were fed the same diet (60% forage: 40% concentrate) for ad libitum intake (except during FR) and water was available at all times. Dry matter intake was measured daily and ruminal pH was recorded every 2 min during FR and recovery periods. Ruminal fluid and blood samples were collected on d 3 of the FR and d 5 of REC1 and REC3. Short-chain fatty acid (SCFA) absorption rates were evaluated on the last day of FR, REC1, and REC3 using the temporarily isolated and washed reticulo-rumen technique. On d 2 of FR and d 4 of REC1 and REC3, a 1 L solution of Cr-EDTA (180 mM) was dosed into the rumen followed by 48 h of total urine collection. Dry matter intake (% BW) increased rapidly in REC1 for heifers restricted to 75 and 50%; however, heifers restricted to 25% needed at least 2 wk to recover (treatment x period; P < 0.001). Regardless of the severity of FR, the duration that pH < 5.5 was the highest during REC1 (period P < 0.001). However, an interaction was found for the acidosis index, with pH x min/kg of DMI being greatest in heifers restricted to 25% on d 1 of the recovery period. A treatment x period interaction was found for the absolute absorption rate (mmol/h) of total SCFA (P = 0.009). The total SCFA absorption rate was not different for heifers restricted to 75 and 50% across periods, whereas an increase from FR and REC1 to REC3 was detected for heifers restricted to 25% of ad libitum intake. A treatment effect was observed for urinary Cr output (P = 0.027) indicating that heifers previously restricted to 25% of ad libitum intake had greater Cr excretion in urine during FR and recovery. This study indicates that severe FR negatively affects the time required for recovery of reticulo-rumen absorptive function and total tract barrier function. Another important finding is that regardless of severity, FR increases risk for ruminal acidosis when heifers have free access to feed after FR.