Effects Of Breeds And Dietary Nutrients Levels On Pax3,Pax7 And MRFs Expression And Meat Quality Of Pigs

Paired box 3(Pax3)and 7(Pax7),along with myogenic regulatory factors(MRFs)were vital to myogenesis.Previous studies were mainly focused on gowing or finishing pigs to research the difference of expression pattern of these myogenic genes,however,the expression profile of mygenic factors in pig muscles in early postnatal period or from the birth to finishing period were reported rarely.It is well documented that dietary nutrients levels altered the composition of myofiber types in pigs muscles,but little is known the alteration of expression of myogenic factors in this process.Based on these,the aim of this study is to investigate the different expression pattern of Pax3,Pax7.MRFs and myofiber types,as well as meat quality in two pig breeds from the birth to finishing period.Furthermore,the effect of moderate low-nutrient level diet on the expression of these myogenic genes and myofiber types and meat quality are also investigated in commercial growing-finishing pigs.Experiment 1.Effects of breeds on Pax3,Pax7 and MRFs expression and meat quality of pig muscles.Five piglets were selected based on average body weight from 5 litters Large white pigs and 5 litters Chenghua pigs respectively.and slaughtered to sample LD(longissimus dorsi),SOL(soleus)and EDL(extensor digitorum longus)at 0,7,14 and 21-day-old.Then,thirty 21-day-old weaned Large white piglets and thirty 21-day-old weaned Chenghua piglets were chose and fed the diets met each breed nutrient requirement.Each breed contained 5 replicates with 6 pigs per replicate.One fasting pig was randomly selected from each replicate to slaughter and sampled LD,SOL and EDL at 63,105,185 and 220-day-old.Results were as follows:1)The expression patterns of myogenic genes and MyHCs in muscles were consistent between Large white pigs and Chenghua pigs.In general,with aging,the expression of myogenic genes,MyHC-Ⅰ and Ila was down-regulated,whereas the expression of MyHC-Ⅱx and Ⅱb was up-regulated.However,myogenic genes and MyHCs mRNA levels in LD were up-regulated during the fast growth period,especially at 105-day-old(P<0.05).2)The relationships between myogenic genes and MyHCs were different among two pig breeds.For Large white pigs,expression of Pax3 and Myf5 were positively related to MyHC-Ⅱa and Ⅱx(r>0.48,P<0.05),while negatively related to MyHC-IIb(r>0.48,P<0.05).Pax7 was positively related to MyHC-Ⅱx and Ⅱb(r>0.3,P<0.05),MyoD was negatively related to MyHC-Ⅰ(r =-0.2,P<0.05).For Chenghua pigs,expressions of myogenic genes were positively related to MyHC-Ⅰ,Ⅱa and Ⅱx(r>0.19.P<0.05),but negatively related to MyHC-IIb(r>-0.19,P<0.05).Furthermore,the LD of Large white pigs expressed lower Pax3,Pax7,Myf5,Mrf4.MyHC-Ⅰ and Ⅱa mRNA(P<0.05),higher MyHC-Ⅱx and Ⅱb mRNA levels(P<0.05)than Chenghua pigs at 105‖220-day-old.The pork quality of Large white pigs was inferior to that of Chenghua pigs during the growing-finishing period.These results indicated that the genotypic differences of relationships between the expression of myogenic genes and MyHC resulted in the different composition of myofiber types in LD,thus induced the different pork quality between Large white pigs and Chenghua pigs.Experiment 2.Effects of dietary nutrient levels on Pax3,Pax7 and MRFs expression and meat quality of pigs.Sixty 21-daxy-old weaned Large white piglets(6.15 ± 0.03kg)were randomly allocated to feed the normal nutrient level diet based on NRC(2012).or to feed low nutrient level diet(averagely reduced by DE:0.13 Mcal/kg.CP:1.48%.Lys:0.35%).Each group contained 5 replicates with 6 pigs per replicate.One fasting pig was selected from each replicate to slaughter and sample LD at 63,105 and 220-day-old.Results were as follows:1)Reduced nutrient level diet had no negative impact on growth performance and carcass quality of growing-finishing Large white pigs,but it decreased the shear force(P<0.001)of LD at 220-day-old.2)There was no significant difference in myogenic factors and myofibers expression at 63-day-old Large white pigs.However,lowered nutrient level diet up-regulated(P<0.05)the mRNA expression of Pax3,MyoG,Mrf4 and MyHC-Ⅱa in 105-day-old Large white pigs,and up-regulated(P<0.05)the mRNA expression of Pax3,Myf5,Mrf4,MyHC-Ⅰ and Ⅱa in 220-day-old,down-regulated(P<0.05)mRNA abundance of MyHC-Ⅱb in 220-day-old Large white pigs.These results suggested that moderate reduced nutrient level diet up-regulated Pax3,Myf5,MyoG and Mr4 mRNA expression,increased oxidative myofiber and decreased glycolytic myofiber expression,thus improved the meat quality of growing-finishing Large white pigs.Based on these results,this study suggested that the genotypic differences of relationships between the expression of myogenic genes and MyHCs resulted in the different composition of myofiber types in LD,thus induced the different meat quality.For the Large white pigs,moderate reduced nutrient level diet up-regulated some myogenic genes,which positively related to oxidative myofibers,to elevate expression of oxidative myofibers and improve meat quality.