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Two 6-week-old barrows from each of five litters (Landrace x Large White) were used (weaned at 4 weeks of age). Each littermate was assigned to one of two diets, control (lysine content: 1.16%) or low lysine (LL) diet (lysine content: 0.73%). The diets were iso-energetic and iso-protein, and contained all essential amino acids (apart from lysine) in the recommended amounts. The pigs were fed these diets for 3 weeks. At the end of the study, samples of l. dorsi and rhomboideus muscles were dissected rapidly, divided into 5g portions, frozen in liquid nitrogen and stored at -80°C until analysis for abundances of peroxisome proliferator-activated receptor coactivator 1 (PGC-1α), peroxisome proliferator-activated receptor 2γ (PPAR-2γ), and GLUT4 mRNA and measurements of activity of citrate synthase (an indicator of oxidative capacity of cell). Glycogen contents in these samples were also determined. For assessment of proportion of oxidative fibers in each muscle, samples of 1cm3 were frozen immediately in isopentane cooled in liquid nitrogen before storage at -80°C. Plasma was stored at -20°C until analysis for free amino acid concentrations.
Dietary lysine levels did not affect feed intake. Growth rates of pigs fed the LL diet tended to be slower than those of the control pigs (P = 0.073), and feed efficiency was lower in the LL group compared with the control group (P 0.05). Citrate synthase activities in both muscles were higher in pigs fed the LL diet compared with the control pigs (P 0.05). Glycogen content in rhomboideus muscle of the pigs fed the LL diet tended to be higher compared with the control pigs (P = 0.127), whereas dietary lysine levels did not affect that in l. dorsi muscle. As expected, plasma lysine concentration was considerably lower in the pigs fed the LL diet (P 0.01). Concentrations of threonine, valine, isoleucine, phenylalanine, histidine, and arginine were higher in the LL group (P 0.05), and those of methionine and leucine tended to be higher (P = 0.0852 and P = 0.0917, respectively) in the LL group. By contrast, those of glutamate and glycine were lower (P 0.05) in the LL group. In both muscles assessed, pigs fed the LL diet had higher proportion of oxidative fiber than those fed the control diet (P 0.01). The abundance of mRNA of GLUT4, PPAR-2γ, and PGC-1α was higher in muscles taken from pigs fed the LL diet (P 0.05) with the exception of those of GLUT4 (P = 0.1037) and PGC-1α (P = 0.5494) mRNAs in l. dorsi muscle.
In conclusion, reducing intake of dietary lysine enhances proportion of oxidative muscle fiber, and hence oxidative capacity of porcine muscle.
M Katsumata, M Matsumoto, S Kobayashi and Y Kaji. 2008. Journal of Animal Science. 2008 79: 347-353.
