Muscle-specific metabolic, histochemical and biochemical responses to a nutritionally induced discontinuous growth path

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Inglés. An experiment was conducted with 42 Montbeliard steers to determine if nutritionally induced interrupted growth could influence muscle characteristics of steers and hence meat quality. A restriction/refeeding path was designed in order to induce a discontinuous growth path. At 9 months of age, 21 steers were given a restricted amount of diet for 3 months and were then slaughtered (R steers; no. = 10; intake : 5.28 kg dry matter (DM) per day) or subjected to a 4-month ad libitum refeeding period (R/F steers; no. = 11; intake : 8.99 kg DM per day) with the same diet (11.03 to 11.12 MJ metabolizable energy (ME) per kg DM) prior to slaughter. An additional 21 control steers were offered the same diet but in amounts that allowed them to gain continuously between 9 and 12 months of age, and were then slaughtered (C steers; no. = 10; intake : 7.08 kg DM per day) or maintained on a continuous feeding protocol through to 16 months of age prior to slaughter (C/C steers; no. = 11; intake : 8.07 kg DM per day). M. semitendinosus (ST), m. longisssimus thoracis and m. triceps brachii ( TB) were collected for biochemical and histochemical analyses. R steers had a lower average daily gain (ADG; P < 0.001), a lower final weight ( P < 0.01) and a leaner carcass (P < 0.01) than C steers. Upon refeeding, R/F steers had a higher ADG than C/C steers (P < 0.05) and underwent compensatory growth resulting in compensation of body weight and composition at 16 months. In muscles, glycolytic lactate dehydrogenase activity was lower in R steers (P < 0.01) and restored in R/F steers compared with control steers. Among oxidative enzymes, cytochrome-c oxidase activity was higher in the TB of R/F compared with C/C steers (P < 0.001) indicating a muscle-specific metabolic adaptation to the feeding level. There was little effect of the nutritional treatment on muscle fibre size and type except for an increase in the frequency of hybrid fibres in R and R/F groups (P < 0.05). Total and insoluble collagen content were affected by restriction (P < 0.001) in a muscle-specific manner : insoluble collagen content was lower in ST, but total and insoluble collagen contents were higher in TB of R compared with C animals at 12 months of age. No differences were recorded in lipid contents nor in proteasome activities. The data suggest that an alternation of relatively mild nutritional restriction and ad libitum feeding had only a small effect on muscle characteristics. However, muscles respond differentially to changes in feeding level.