Animal Science Department


Date of this Version



Published in Journal of Animal Science 1990. 68:2707-2715. Copyright © 1990 American Society of Animal Science. Used by permission.


The objective of this study was to determine the effect of feed restriction and repletion on myofibrillar protein turnover in cattle. Crossbred steer calves (n = 12) about 310 d of age were assigned randomly to a diet of corn and silage that was 1) provided ad libitum for 146 d (ALC) or 2) restricted so steers gained .2 kg/d for 80 d but received ad libitum access to feed thereafter for 66 d (RFC). At 27, 55, 97, 118 and 146 d a 24-h urine sample and a blood sample were obtained. Urine was analyzed for Nτ-methylhistidine Nτ-MH), creatinine (C), urea nitrogen (UN) and total nitrogen (TN). Serum samples were analyzed for hydroxyproliine (HYF'), C and albumin (A). Body weights were lower (P < .05) in RFC at 55, 97, 118 and 146 d. Excretion of Nτ-MH was lower (P < .05) in the RFC at 27 and 55 d but higher at 118 d Urinary C excretion was higher in ALC at the last four sample times. Urinary UN and TN excretion were lower (P < .05) in RFC at 55, 97 and 118 d; urinary UN also was lower (P < .05) at d 146. Serum A was higher (P < .05) in ALC at 55 and 118 d, respectively. Serum HYP was higher (P < .05) in RFC at 27 and 55 d. Calculated myofibrillar protein breakdown rates (FBR) and fractional synthesis rates (FSR) were higher (P < .05) in RFC at the last two sampling periods; FSR was lower for the RFC at the first sampling period. Realimentation after a period of feed restriction increased both synthesis and degradation of myofibrillar protein in beef cattle.