Differential growth retardation and Myofibrillar fragmentation in rats submitted to feed restriction and realimentation

Abstract

Feed regimens alter muscle growth rate, hence they might impact the proteolytic system involved in tenderization during meat conditioning. The aim of this project was to verify the effects of feed restriction regimens on muscular and animal growth and their impact on postmortem myofibrillar fragmentation. The regimens were: 1) Feeding ad libitum for 11 d (Al/2); 2) Feed restriction (60% of Net Energy for maintenance - NEm) for 11 d (Rt/2); 3) Ad libitum for 22 d (Al); 4) Ad libitum for 4 d and feed restriction (60% NEm) for 18 d (Rt); 5) Ad libitum for 19 d and 3 d of fast (Ft); 6) Feed restriction (60% NEm) for 11 d and ad libitum until 22 d (Ral). The regimens Al/2 and Rt/2 had different intestine weights (19.3 ± 1.1 and 15.8 ± 1.9 g, respectively; P < 0.07). At 22 d, Al animals had higher (P < 0.07) intestine weight (21.8 ± 3.8). Moreover, Ral animals had heavier intestine (19.9 ± 1.5) as compared to Rt (16.6 ± 1.6) or Ft (12.8 ± 1.9). The intestine/live weight percentage ratio was lower (P < 0.05) for Ft (6.3%) as compared to Al (8.4%) and to Ral (9.2%), but it was similar to Rt (7.6%). Liver weight (g) in the Ral (9.5 ± 1.1) did not differ from Al (10.7 ± 2.5) or Rt (8.5 ± 1.1), although the two latter were different (P < 0.05). There was an effect of feed restriction over muscle protein degradation verified by Myofibrillar Fragmentation Index (MFI). The animals at Rt, Ft or Ral showed the lowest MFI 0d (42 ± 1.9; 40 ± 2.7; 40 ± 3.6; respectively) and MFI 5d (77 ± 2.7; 74 ± 3.0; 74 ± 2.9; respectively) as compared to Al, whose indexes were 54 ± 3.0 and 82 ± 3.3. Even though the MFI 5d were lower for the restricted animals, the rates of fragmentation postmortem were higher. Feed restriction altered myofibrillar protein degradation, reflected in lower extended fragmentation of the myofibrils.