Effects Of Driving Stress On Pork Quality And Its Control

Pork quality is closely related to the preslaughter stress,and the sources of stress include the transportation,lairage,driving,air temperature and slaughter methods,among which the driving stress has the greatest influence on the quality of pork.In China,slaughtering enterprises pay little attention to the stress caused by pre-slaughter driving.Most of them use electric shocks,whips and other methods to drive pigs forward.Pigs have very serious stress and low animal welfare level.Due to the acute stress before slaughter,the energy metabolism rate in the pigs is accelerated and a large amount of muscle glycogen is consumed,which eventually leads to the decline of meat quality.However,the biochemical mechanism causing such changes in energy metabolism is not clear.At present,more and more researchers believe that the key enzymes in the regulation of energy metabolism pathways are important factors causing energy changes,and these regulatory enzymes often undergo protein modifications(especially phosphorylation and acetylation modifications),and thus become more active,ultimately affecting the change of the whole energy pathway.Therefore,it is of great significance to explore the influence of stress on the modification of energy metabolism proteins to explain the mechanism how these proteins affect meat quality.This study adopted mild driving,sound and smell driving and traditional methods to explore how preslaughter driving affect blood stress indicators,meat quality and energy metabolism and used proteomics,phosphorylated proteomics and acetylated proteomics to analyze the regulatory effects of stress on muscle energy metabolic enzymes,and to explain the potential factors affecting meat quality.Finally,according to results,two sets of equipment were designed and completed to improve the pre-slaughter management of pigs,so as to provide technical support for production.1.Effects of different driving methods on animal welfare,blood stress and meat quality of pigsIn winter and summer,45 pigs(6 months old)were randomly categorized into three treatments:(?)mild driving(MD);(?)sound and smell driving(SSD);(?)traditional driving(TD).Blood stress,muscle quality and physical and chemical indexes were measured after slaughter.The stress behaviors under different driving methods were analyzed and the welfare of pigs before slaughter was evaluated.In summer,compared with the TD group,the MD group and SSD group showed a decrease in the frequency of stress behavior,and the animal welfare was significantly improved.In the blood,results indicated that the contents of CK,LDH and CORT in the MD and SSD groups decreased(P<0.05)in comparison to TD group.With regard to meat quality,compared with TD treatment,MD and SSD treatments had a higher(P<0.05)redness value and a lower(P<0.05)rate of cooking loss.Meanwhile,the pH at 45 min and 3 h after slaughter increased significantly(P<0.05).In terms of muscle energy metabolism,glycogen and ATP content in the MD and SSD group significantly increased(P<0.05)at 45 min and 3 h postmortem in comparison to TD group.In addition,compared with SSD group,the content of creatine kinase decreased significantly in the MD group(P<0.05),and the incidence of PSE decreased.In winter,compared with the TD group,the a*,b*and cooking loss in MD group were significantly increased(P<0.05).The incidence of DFD meat decreased,and the postmortem pH drop rate was normal(the TD group was always higher than 6.0),and the ATP content was significantly increased after 45 min and 3 h(P<0.05).In addition,the glycogen content at 45 min,3 h and 12 h postmortem in MD group were higher than the other two groups(P<0.05).These results show that mild driving and sound and smell driving can reduce the pre-slaughter stress of pigs,improve animal welfare,and improve pork quality.2.Effect of proteins and protein post-modifications on muscle energy metabolismIn order to explore the underlying mechanism affecting pork quality caused by pre-slaughter driving stress,muscle samples(45 min postmortem)of 6 pigs were selected from the MD group and TD group in winter,and differences of modified proteins in muscles were analyzed using phosphorylated proteomics and acetylated proteomics techniques.In terms of proteomics,compared with TD group,the expression levels of 13 proteins in MD group were increased,and 5 proteins were decreased(P<0.05,the quantitative expression difference between the groups was greater than 1.2).Differentially expressed proteins are involved in muscle contraction and energy metabolism.In the phosphorylated protein group,compared with TD group,131 phosphopeptides(65 upregulated peptides and 66 upregulated peptides)in the MD group showed significant difference(P<0.05,the quantitative expression difference between the groups was greater than 1.2),which correspond to 39 upregulated and 37 upregulated phosphopeptides.Biological functions of these proteins include energy metabolism,muscle contraction,signal transduction,calcium regulation,stress and defense,and cellular structural components.Through bioinformatics analysis,it was found that protein phosphorylation in closely connected pathways,glycolysis/gluconeogenesis,carbon metabolism and other related pathways were significantly different.Among them,GAPDH,EN03,PYGM,PGM1,ACTA1,ACTN2,TNNI1,MYH4 and MYH7 play key roles.In the acetylated protein group,compared with the TD group,26 acetylated peptides showed significant difference in MD group(P<0.05,the quantitative expression difference between the groups was greater than 1.2),including 20 upregulated peptides and 6 upregulated peptides,corresponding to 13 upregulated and 5 upregulated acetylated proteins,respectively.The biological functions of these proteins are related to energy metabolism and muscle regulation,involving tight junction,glycolysis/gluconeogenesis,carbon metabolism,glycogen metabolism.The proteins included ENO3,PYGM,CKM in the energy pathway and MYH1,MYH4 and MYH7 in muscle regulation.Overall,energy metabolism enzymes,phosphorylation(GAPDH,PGK1,etc.)and acetylation(ALDOA,ENO,LDHA,etc.)can jointly promote energy metabolism and regulate glycogen metabolism and glycolysis pathways.Phosphorylation and acetylation regulate muscle contraction through energy metabolism.Myosin and actin can be phosphorylated and deacetylated to regulate the thick and thin filament in myofibrils and promote muscle contraction.3.Design of pre-slaughter handling equipmentConsidering the relatively insufficient animal welfare and low degree of system automation in our country,we designed two sets of equipment to improve the pre-slaughter management.The first equipment is a new kind of pre-slaughter handling device for domestic small and medium-sized enterprise.This equipment combines various factors which are beneficial to pigs,to a large extent reduces the pigs in the process of stress reaction and improves the pig animal welfare.The staff deals with the device in the control room.Compared with the existing way,this device reduces the cost of manpower input and management before slaughter.The second equipment is an automatic pre-slaughter management system for large domestic and foreign slaughtering enterprises.The whole pre-slaughter management system enables the handling process to be mechanized and intelligent from unloading,driving,resting,flushing,transportation and stun.At the same time,the pigs were in a state of rest during the whole pre-slaughter management process without any electric shock,which greatly reduced the stress and improved the animal welfare.Moreover,the whole lairage area will be an empty ground,which can benefit the environment of the slaughter-house.