Effect of the Severity of Short-Term Feed Restriction on Gut Function

The objective of this study was to evaluate whether different severities of short-term feed restriction (FR) affect the absorptive function of the reticulo-rumen and total tract barrier function in beef cattle and also to determine the timeline for recovery of these functions. Eighteen ruminally cannulated and ovariectomized Angus × Hereford heifers were blocked by BW and randomly assigned to 1 of 3 treatments differing in the severity of FR. Feed offered was restricted to 75, 50 and 25% of the ad libitum feed intake measured during FR relative to that measured during the 5-d baseline period (BASE). Feed restriction (FR) was imposed for 5 d followed by 3 consecutive wk of recovery in which cattle were fed ad libitum (REC1, REC2 and REC3). Throughout the study, heifers were housed in individual pens (9 m2) and were fed the same diet (60% forage: 40% concentrate) with free access to water. Dry matter intake (DMI) was measured daily and ruminal pH was measured every 2 min throughout the study. Ruminal fluid and blood samples were collected on d 3 of the BASE and FR and on d 5 of REC1 and REC3. The temporarily isolated and washed reticulo-rumen technique (WRR) was used to evaluate short-chain fatty acid (SCFA) absorption on the last day of BASE, FR, REC1 and REC3. Total tract barrier function was evaluated starting on d 2 of the BASE and FR and on d 4 of REC1 and REC3 using a pulse dose of chromium ethylenediaminetetraacetic acid (Cr-EDTA) followed by 48-h of total urine collection. Dry matter intake did not differ among treatments during BASE but, as imposed by the experimental model, DMI during FR relative to BASE equated to 70, 49, and 25%, which was close to the targeted values of 75, 50, and 25% (treatment × period, P < 0.001). A treatment × period interaction (P < 0.001) was also detected for SCFA concentration with the concentration decreasing as the severity of FR increased, whereas there were no differences during BASE. Absorption of SCFA across the reticulo-rumen tended to decrease with increasing severity of FR (P = 0.080). Acetate absorption (mmol/h) decreased (P = 0.050) by almost 70 mmol/h at 25 and 50% feed relative to BASE (322 mmol/h). Heifers restricted to 25% feed had greater urinary Cr recovery during FR than BASE while no changes were detected for those restricted to 75 and 50%. After FR, DMI (% 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 × period, P < 0.001). Regardless of the severity of FR, the duration that pH < 5.5 was highest during REC1 (period P < 0.001). A treatment × period interaction was observed for the absolute absorption rate of total SCFA (P = 0.009) where the total SCFA absorption rate was not different for heifers restricted to 75 and 50% across periods while 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 recovery. This study indicates that moderate short-term FR has negative effects on the absorptive function of the reticulo-rumen but more severe FR is required to compromise total tract barrier function in beef cattle. Severe FR also negatively affects the time required for recovery of reticulo-rumen absorptive function and total tract barrier function. Regardless of severity, FR increases risk for ruminal acidosis when heifers have free access to feed after FR