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Article

Restricted Feed Intake during Fattening Reduces Intramuscular Lipid Deposition without Modifying Muscle Fiber Characteristics in Rabbits¹

Florence Gondret^*2, François Lebas and Michel Bonneau^*

^* Institut National de la Recherche Agronomique, Station de Recherches Porcines, 35590 Saint Gilles Institut National de la Recherche Agronomique, Station de Recherches Cunicoles, 31326 Castanet Tolosan Cedex, France

²To whom correspondence should be addressed.

The present study was conducted to determine the effects of feed restriction during fattening on muscle fiber characteristics and intramuscular lipid traits. From 11 wk of age onward, rabbits were given free access to feed (control group), or received 70% of the control feed intake (restricted group). At the same weight at slaughter, restricted-fed rabbits were 3 wk older than controls (18 vs. 15 wk). The longissimus lumborum (LL, white loin), biceps femoris (BF, white thigh) and semimembranosus proprius (SMP, red thigh) muscles were then removed, and biochemical and histochemical assays were performed. In the three muscles, there was no effect of feed restriction on mean fiber size or percentage of the different fiber types. Restricted vs. control feeding resulted in a significant reduction (P < 0.001) in total lipid content in all three muscles. This reduction was paralleled by a decline (P < 0.001) in the activities of the malic enzyme and glucose-6 phosphate dehydrogenase (G6PDH), generating NADPH for the support of fatty acid synthesis. The diet-induced variations in lipid concentration and enzyme activities were larger (P < 0.05) in the pure oxidative SMP muscle than in the predominantly fast-twitch glycolytic LL and BF muscles. Whatever feeding status, the ratio of malic enzyme to G6PDH activities was sharply lower (P < 0.001) in SMP than in BF and LL muscles (averaging 1.5 vs. 9 and 15, respectively). These data indicate that nutritional status regulates intramuscular lipid deposition, without changing fiber-type composition. Further studies are necessary to determine the role of G6PDH in the lipogenic process of oxidative vs. glycolytic muscles.

KEY WORDS: • food restriction • myofiber • intramuscular fat • lipogenesis • rabbits

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