Effects of Dietary Protein Level and Breeds on Myosin Heavy Chain Composition and Meat Quality in growing-finishing Pigs

Both dietary protein level and myosin heavy chains (MyHC) composition of muscle affect meat quality, so we hypothesized that the dietary protein level affect meat quality partially by changing the composition of MyHC isoforms and the effect of ditary protein level on MyHC composition was different between breeds. Duroc ×Landrace× Yorkshire (DLY) (n=12, 150-day-old) and MeiShan pigs (n=12, 150-day-old) were allocated into 4 treatments arranged factorially, including 2 dietary levels of protein (high or low) and 2 breeds (DLY or MeiShan) by body weight and sex. There were one pig per pen, and feed and water were available ad libitum. At the same age, the body weight and loin eye area of DEY were higher (P＜0.05), but the values of pH(subscript 24h) and b(superscript *)(subscript 24h) were lower (P＜0.05) than that of MeiShan. The proportion of MyHC ha, oxidative fiber (MyHC I and MyHC IIa) of MeiShan was higher (P＜0.05), but the proportion of MyHC IIx was lower (P＜0.05) than that of DLY. A significant interaction was observed (P＜0.10) between breed and dietary protein level for the proportion of MyHC IIb, MyHC IIx. There was a positive correlation (P＜0.05) between MyHC ha and L(superscript *) value and a negative correlation (P＜0.05) between MyHC lib and IMF. There was a positive correlation (P＜0.05) between MyHC IIx and L(superscript *) value and a correlation (P＜0.01) between MyHC IIx and pH. The correlation coefficients of oxidative fiber (MyHC I and MyHC IIa) were also highly significant (P＜0.01) for b(superscript *) value and pH. In conclusion, the meat quality and MyHC isoforms composition were different between breeds, and the MyHC composition and meat quality of DLY were more sensitive to low protein diet than MeiShan. Feeding pigs with low protein diet could improve meat quality, but was not an effective way to alter MyHC composition. These data indicate that dietary protein affected meat quality not by altering MyHC composition.