Effects Of Nutrition And Breed Levels On Myofibre Types And Pork Meat Quality In Pigs

Three experiments were carried out to investigate the effects of breeds, dietary crude protein and energy levels on carcass quality, meat quality, and myofibre types in longissimus dorsi (LM) in finishing pigs, and the correlationship between meat quality and myofibre types was also analyzed.Exp. 1. The effect of breeds on meat quality and myofibre types in finishing pigsThe objective of this experiment was to investigate the difference of the profile of myosin heavy chains (MyHC) among pig breeds under the condition of enlengthening the time of finishing-phase, and the correlationship between meat quality and the profile of MyHC was also analyzed. The completely randomized experimental design was used. Three breeds were chose as MeiShan, DuMei (Duroc×MeiShan), and DLY (Duroc×Landrace×Yorkshire), with 6 pigs of each breeds. All the pigs were fed the same diet and slaughtered at the 240-day-old. The loin eye area, backfat thickness, pH of meat, meat color, driploss and intramuscular fat (IMF) were measured and the relative mRNA expression levels of 4 MyHC isoforms in LM were detected by real time RT-PCR. 1) The body weight and loin eye area of DLY were significantly higher (P<0.05) than that of DuMei, and body weight and loin eye area of DuMei were significantly higher (P<0.05) than that of MeiShan. The values of pH_45min, pH_24h, and b_45min of DLY were significantly lower (P<0.05) than that of DuMei and MeiShan. The value of a_45min of Meishan was higher than that of DuMei, and the DLY was the lowest, but the difference was not significant (P=0.083). The IMF contents in LM were different among pig breeds (P=0.054). The IMF of DuTai was the higher than that of MeiShan and DLY. 2) The proportions of MyHC I in MeiShan and DuMei were significantly higher (P<0.1) than that of DLY, and the proportion of MyHC IIa in MeiShan was significantly higher (P<0.1) than that of DLY and DuMei, and the proportion of oxidized myofibres in MeiShan was significantly higher (P<0.1) than that of DLY. 3) There was a significant (P<0.05) negative correlation between the proportion of MyHC I and driploss, and a significant (P<0.05) positive correlation between the proportion of MyHC IIa and pH was observed.Exp. 2. The effects of dietary crude protein levels on myofibre types, carcass quality,and meat quality in later period of finishing pigsThe objective of this experiment was to investigate the effect of dietary crude protein level on meat quality and the profile of myosin heavy chains (MyHC) in LM, and to clarity the correlationship between myofibre types and meat quality. The 2×2 factorial experimental design was used. The two breeds were Duroc×Landrace×Yorkshire (DLY) and MeiShan, and two diets were high crude protein level diet and low crude protein level diet. Twelve 150-day-old DLY and twelve MeiShan pigs were allocated to four treatments with 6 replications of 1 pig each based on bodyweight and sex of the pigs. After a 90-day -experiment, all the pigs were slaughtered and samples were collected, and the loin eye area, backfat thickness, pH of the meat, meat color, driploss and IMF were measured, and the relative mRNA expression levels of 4 MyHC isoforms in LM were detected by real time RT-PCR. 1) Low dietary crude protein level significantly improved (P<0.05) the IMF content in DLY, and the proportion of MyHC IIb of DLY feeding the low crude protein diet was significantly (P<0.10) lower than that feeding the high crude protein diet, and the proportion of MyHC IIx of DLY feeding the low crude protein diet was significantly (P<0.10) higher than that feeding the high crude protein diet (49.71 vs 40.88). 2) Feeding low crude protein diet had the tendency to improve the IMF content in MeiShan. The proportion of MyHC IIa of MeiShan feeding the low crude protein diet was higher than that feeding the high crude protein diet, but the proportion of MyHC IIx was significantly lower (P<0.10). 3) There was a significant (P<0.05) negative correlation between the proportion of MyHC IIb and IMF content, and a significant (P<0.05) positive correlation between the proportion of oxidized myofibres and pH was observed.Exp. 3. The effects of dietary energy levels on myofibre types, carcass quality, andmeat quality in later period of finishing pigsThe objective of this experiment was to investigate the effect of dietary eneryg level on meat quality and the profile of myosin heavy chains (MyHC) in LM, and to clarity the correlationship between myofibre types and meat quality. Twenty-two Duroc×Landrace×Yorkshire (DLY) pigs (average body weight 20 kg) were allocated into two groups (control and high-energy) randomly and each group had 11 replications of 1 pig. The diets for each stage of the high-energy group pigs were formulated by adding 3%, 5%, 7% animal fat in the corresponding basal diets for control group pigs of 20-50 kg, 50-80 kg, 80-120 kg body weight. The loin eye area, backfat thickness, pH of the meat, meat color, driploss and IMF were measured and the relative mRNA expression levels of 4 MyHC isoforms in LM were detected by real time RT-PCR. 1) Adding animal fat to diet significantly improved (P<0.05) the pK_45min, IMF and proportions of MyHC IIa and IIx, and decreased the proportion of MyHC IIb highly significantly (P<0.01). There were positive correlations between the proportion of MyHC I and pH_45min (P<0.01), a_45min (P<0.05), b_45min (P=0.05) and IMF, and a negative correlation between the proportion of MyHC I and driploss was observed (P=0.05).In conclusion, 1) The proportion of oxidized myofibres of 240-day-old MeiShan and DuMei pigs was higher than that of DLY, and the IMF of DLY could improved by appropriately lengthening the time of finishing phase; 2) The dietary crude protein level affected the profile of myofibre types and had a greater impact on regulating the meat quality and myofire types in DLY than that of MeiShan; 3) increasing the dietary energy level could increase the proportion of oxidized myofibres of DLY; 4) the profile of myofibre had influence on meat quality, and there was a positive correlationship between oxidized myofibres and meat quality.