Compensatory growth response in pigs, muscle protein turn-over and meat texture: effects of restriction/realimentation period

The present experiment was designed to evaluate the effect of different time spans of ad libitum feeding of pigs prior to slaughter after a period of restricted feeding on performance and texture characteristics of the meat. Ten litters of five pigs (Duroc X Landrace X Large White crosses) were allocated to five feeding treatments (AA, R(28)A(42), R(43)A(27), R(52)A(18) and R(60)A(10)) at the age of 70 days. AA-pigs were given ad libitum a concentrate diet from day 70 to slaughter at day 140 (approx. 100 kg live weight). R(28)A(42), R(43)A(27), R(52)A(18) and R(60)A(10) Pigs were given food at a restricted level (0.6 of ad libitum)for 28, 43, 52 and 60 days, respectively, followed by ad libitum feeding for 42, 27, 18 and 10 days, respectively, until slaughter at day 140. All pigs that had been given food at a restricted level for a period (R(28)A(42), R(43)A(27), R(52)A(18) and R(60)A(10)) showed a compensatory growth response in the subsequent ad libitum period. However, only pigs on ad libitum for a minimum of 27 days prior to slaughter (R(28)A(42) and R(43)A(27)) had carcass weights and muscle mass similar to that of the control pigs (AA) at slaughter. The restricted feeding increased meat proportion, whereas the feeding strategies had no effect on technological meat quality traits (pH(24), drip loss and CIE-colour traits : L*, a* and b*). During compensatory growth, protein turn-over was increased and positively related to the length of the ad libitum period as indicated by the concentration Of elongation factor-2 (eEF-2) (P < 0.10), the activity of mu-calpain (P < 0.01) and the myofibrillar fragmentation index (MFI) 1 day post mortem. in m. longissimus dorsi (P < 0.08) and the solubility of collagen (P < 0.01). Although not significant, the shear force at day 1 followed the same pattern of improvement as the MFI. The concentration of eEF-2 increased at a faster rate following transition to ad libitum feeding than did the activity of mu-calpain. This suggests that muscle protein synthesis increases at a faster rate after change to ad libitum feeding and reaches the same level as in the control pigs (AA) before muscle protein degradation. This time lag between the increase in protein synthesis and degradation could explain the compensatory growth response and it also suggests that in order to use the compensatory growth mechanism to improve tenderness, the optimal time of slaughter may not coincide with the period of highest growth rates, but may occur at a later stage, when muscle protein degradation is maximal. For pigs slaughtered at 100 kg live weight, we expect muscle protein degradation to be maximal some time beyond 42 days of ad libitum feeding prior to slaughter.