L-Carnitine supplementation during suckling intensifies the early postnatal skeletal myofiber formation in piglets of low birth weight1

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Piglets of low birth weight exhibit a reduced total number of skeletal myofibers at birth and throughout life compared with piglets of middle and heavy birth weight, which is associated with impaired (lean) growth and quality of carcass and meat at market weight. We investigated the effect of L-carnitine supplementation to suckling piglets of different birth weights on early postnatal myofiber formation, muscle growth, and body composition. A total of 48 piglets of low (LW) and middle (MDW) birth weight from 9 German Landrace gilts received 400 mg of L-carnitine (carnitine, n = 25) or a placebo (control, n = 23) once daily from d 7 to 27 of age and were slaughtered on d 28 of age (weaning). Carnitine-supplemented piglets deposited less fat as indicated by a reduced proportion of perirenal (P = 0.1) and intramuscular fat (P = 0.05). Circulating glucose concentrations tended to be greater in supplemented LW piglets (P = 0.13). The concentration of carnitine in semitendinosus (STN) muscle was approximately doubled (P < 0.001) by supplementation, with emphasis on the proportion of esterified carnitine. The ratio of lactate dehydrogenase to isocitrate dehydrogenase tended (P = 0.12) to be smaller in STN muscle of supplemented piglets, indicating a more oxidative muscle metabolism. The total number of STN myofibers was increased by 13% (P = 0.02) in supplemented LW piglets, thereby reaching the unchanged level of MDW littermates. In addition, supplemented LW piglets displayed a 2.4-fold mRNA expression of the gene encoding the embryonic isoform of the myosin heavy chain in STN muscle than control piglets (P = 0.05), but there were no differences in the proportion of fibers positively staining for the embryonic myosin isoform. L-carnitine-supplemented piglets exhibited a greater DNA:protein ratio (P = 0.02) in STN muscle, which resulted from a greater DNA concentration (P = 0.04). However, the STN muscle of L-carnitine-supplemented piglets was not less mature as indicated by unchanged myofiber size, creatine kinase activity, and protein concentration. The results indicate that energy balance has been improved through intensified fatty acid oxidation. As a consequence, myogenic proliferation appears to be stimulated, which in LW piglets may have contributed to a compensatory increase in myofiber number. Thus, piglets, particularly those of low birth weight, could profit from an early postnatal L-carnitine supplementation, which may attenuate the negative consequences of low birth weight on body composition and meat quality at market weight.