Effects And Underlying Mechanisms Of Muscle Fibre Types On Pork Quality

Improving pork quality through changing the muscle fibre types is a focus in the fields ofmeat science and pig production. Firstly the law of MyHC expression in porcine longissimudoris (LD) was studied during the different growth stages after birth. Then taking differentpercentage of native bloodline pigs as objects, the breed difference of muscle fibre types andits association with pork quality traits were analyzed, and the underlying molecularmechanisms were further studied. Lastly dietary modification on muscle fibre types and porkquality in late finishing pigs was conducted.Study on postnatal growth law of MyHC expression in porcine LD. Five DLY(Duroc×Landrace×Yorshire) crossbred pigs were selected at the age of7,40,60,120and175days, respectively. MyHC isoforms, MyHC mRNA and activities of succinate dehydrogenase(SDH) and malate dehydrogenase (MDH) were measured, and the associations among themwere analyzed. The results showed that MyHC mRNA was more likely to be changed thanMyHC isoform, and MyHC mRNA proportion was positively related to the correspondingisoform proportion (P<0.05), simultaneously MyHC I mRNA proportion was positivelyrelated to the activities of SDH and MDH (P<0.05). The analysis of muscle fibre typesaccording to MyHC mRNA composition showed that slow-oxidative fibre was obviouslydecreased with the days of age increasing during postnatal period (P<0.05), and other fibretypes was opposite. From7to60days of age, all fibre types exhibited obviously undulatechanges. From120to175days of age, fast-oxidative, fast-glycolytic and intermediate-typefibre exhibited no significant changes (P>0.05), while slow-oxidative fibre decreasedsignificantly (P<0.05). The above results indicated that MyHC mRNA proportion wassuitably used to analyze muscle fibre types; the conversion among different myofibre typesmainly occured at the early growth stage, and also could be changed during the late finishingperiod.Study on genetic diversity of muscle fibre types and its association with porkquality traits. Jinhua pigs (JHP), Zhejiang Zhongbai pigs (ZBP), Duroc×ZB crossbred pigs(DZP) and Duroc×Yorshire×Landrace (DYL) pigs, which contains100%,12.5%,6.25%and0%of JHP bloodline repectively, were selected, eight pigs per genotype. Muscle fibre types(MyHC mRNA proportions) and pork quality traits in LD were measured. The results showedthat JHP had more slow-oxidative, fast-oxidative and intermediate-type fibre, lessfast-glycolytic firbe in than other genotypes (P<0.05); slow-oxidative fibre decreasedsignificantly in the order of JHP>ZBP>DZP>DYL (P<0.05), fast-oxidative fibre exhibitedthe similar tendency but no significant difference between ZBP and DZP (P>0.05);fast-oxidative and intermediate-type fibre exhibited no significant difference among ZBP,DZP and DYL (P>0.05); slow-and fast-oxidative type fibre were positively related to huantera*, intramuscularly fat (IMF) content and protein solubility, negatively to ΔpH (P<0.05).The above results confirmed the genotypic difference of muscle fibre types, explained pork quality charastics in LD of different genotypes, and indicated that it is beneficial for porkquality by increasing oxidative-type fibre to introduce a certain percentage of native pig breedinto commercial crossbred pigs.Study on energy metabolism related to muscle fibre types. Glycometabolite,phosphate compounds and creatine kinase (CK) activity in LD from JHP (high slow-oxidativefibre proportion, HSO) and DYL (low slow-oxidative fibre proportion, LSO) were measured.The results showed that HSO muscle had the higher CK activity and Cr:(creatinephosphate(CP)+Cr), the more inosine monophosphate (IMP) and creatine (Cr), the lowerglycolysis potential (GP), and the less CP, glycogen, glucose, and glucose-6-phosphate thanLSO muscle (P<0.05); CK activity and Cr:(CP+Cr) were positively related to pH and thepercentages of slow-oxidative, fast-oxidative and intermediate-type fribre, negatively to thepercentage of fast-glycolytic type (P<0.05), the relationships between glucose-6-phosphatecontent, GP and muscle fibre types, pH were opposite; The above results revealed theenergy metabolism mechanism of muscle fibre types influencing pork quality that HSOmuscle had a relatively strong phosphate conversion capacity and a relatively weak glycolyticcapacity.Differential analyses of proteome and gene expression profiling related to musclefibre types. Differential analyses of sarcoplasmic proteome and gene expression profilingwere performed between HSO (JHP) and LSO (DYL) muscle. The results showed that HSOmuscle had the higher contents of nesprin-2-like protein, heat shock protein (HSP)60\70\90,transferring, Gc protein, ATP synthase in mitochondrion and cAMP protein kinase (PKA)(P<0.05), and the lower the contents of glycogen phosphorylase and glucose phosphomutasethan LSO muscle (P<0.05); the up-expressed genes with more than three folds in HSOmuscle were classified into ten categories including immunological reaction, signal transduction,formation of cystoskeleton and connective tissue, metabolic regulation, oxidation resistance,ionic transport, lipid metabolism, nucleic acid metabolism and oxidative phosphorylation, andthe genes in signal transduction were related to the signal pathways of Jak-STAT、cAMP、TGF-β、MAPK and Wnt. The above results revealed the molecular mechanism of muscle fibretypes influencing pork quality that HSO muscle had the relatively strong capacities ofoxidative metabolism, cystoskeleton and connective tissue synthesis, ATP synthesis inmitochondrion, oxidative stress resistance. And the role of Wnt pathway on the differentiationof oxidative-type fibre in porcine muscle was worthy to be concerned and further studied.Nutritional regulation of muscle fibre types in the late finishing pigs.45DZcrossbred pigs (about70kg bodyweight) were divided into three groups (five replicates/group, three pigs/replicate), which were fed with control diet, control+1.2%CLA, control+0.5%CMH, respectively. The feeding experiment lasted for30days, and growth performance,carcass traits, muscle fibre types (MyHC mRNA proportions) and pork quality traits in LDwere measured. The results showed that there was a tendency of promoting granulation,reducing fat deposition, raising pH and hunter a*in the groups of CLA and CMH (P>0.05); slow-oxidative fibre proportion, shear force and protein solubility were significantly increased,and drip loss and milling loss were significantly decreased in CLA group (P<0.05); except forpH, the changing degrees of other pork quality traits was lower in CMH than those in CLAgroup. The above results confirmed the former hypothesis that muscle fibre types could bechanged during the late finishing period, and supplied a new explaination for the mechanismof CLA improving pork quality.This study determined MyHC mRNA proportion as the scientific index for analyzingmuscle fibre types in pigs, and suggested that the porcine muscle fibre types could be changedduring the late finishing period, which was confirmed through feeding experiment. Therelationship between muscle fibre types and pork quality was firstly studied according toMyHC mRNA proportions through the pig populations with different percentage of native pigbreed, and the underlying mechanism was investigated through energy metabolism,sarcoplasmic proteome and gene expression profiling. The conclusion would provide theevidences for high quality pork production, utilization of native pig breed and nutritionalregulation of pork quality.