Study On The Regulation Mechanism Of Castration To Improve The Meat Quality Of Rooster Flavor

Chicken is very popular with consumers because of its delicate taste and excellent flavor,and the content of intramuscular fat(IMF)is one of the important factors to improve the flavor quality of chicken.Castration can improve the flavor quality of chicken by changing the secretion of gonadal axis hormone,but its regulation mechanism is not completely clear.In this study,a cock castration model was made from 4-week-old Wuding chickens,and the changes of the content of the IMF,the level of gonadal axis hormone in the serum,the fatty acid composition in the pectoral muscle,the type and content of volatile flavor substances were analyzed by normal roosters and hens as the control.In order to explore the regulation mechanism of castration on chicken flavor quality,differentially expressed genes(DEGs)in pectoral muscle were screened and their KEGG pathways were enriched by RNA-seq analysis.(1)After 8 weeks of castration,the crown length,crown height and crown weight which is the secondary sexual characteristics were significantly lower than those of the control cocks,higher than those of the control hens(P < 0.05),which indicated that the castration model was successfully established;The content of testosterone(T)in castrated roosters was significantly lower than that of the control cocks,but significantly higher than that of the control hens(P < 0.05);The estrogen(E2)content of castrated cocks was lower than that of control cocks,but the difference was not significant,and lower than that of control hens significantly(P < 0.05);There was no significant difference in follicle stimulating hormone(FSH)content among the three groups.The IMF content of castrated roosters was higher than that of control roosters and lower than that of control hens,but both of the difference was not significant,while that of control hens was significantly higher than that of control roosters.There was a negative correlation between T content in serum and IMF content.(2)After 8 weeks of castration,the percentage of fatty acids such as palmitoleic acid(C16:1),oleic acid(C18:1n9c),linoleic acid(C18:2n6c)and linolenic acid(C18:3n3)in pectoral muscle showed an upward trend,while the percentage of fatty acids such as arachidonic acid(C20:4n6),EPA(C20:5n3)and DHA(C22:6n3)showed a downwardtrend.Similarly,the percentage content of hexanal,heptaldehyde,decanal,nonanal and other flavor substances that contribute greatly to the flavor quality in pectoral muscles showed an increasing trend,which may be due to the lag of the regulation effect of these fatty acids and flavor substances,resulting in no significant difference in different groups,but there has been a corresponding trend.It suggested that the flavor quality of cocks was improved after castration.(3)The transcriptome sequencing results showed that the DEGs screened from(castrated cock/control cock)are mainly enriched in PPAR,glycerol metabolism and other KEGG pathways,including 81 lipid metabolism-related DEGs;the DEGs screened from(control hen/control cock)were enriched to PPAR,MAPK and other KEGG pathways,including 90 DEGs related to fat metabolism;Among them,43 DEGs related to fat metabolism were differentially expressed in differrent groups.LPL,PPARG,APOA1,FADS2,ELOVL6,SLC27A1 and other differentially expressed genes related to fat or fatty acid metabolism were up-regulated or down-regulated among different groups,which together promoted fat deposition.It is suggested that castration of cocks may ultimately improve the flavor quality of chicken by increasing IMF deposition and changing fatty acid composition.However,only 100 DEGs were screened in(castrated rooster/control hen),and no KEGG pathway was significantly enriched,which indicated that the gene expression pattern of castrated cocks was similar to that of hens;To sum up,after castration,the expression of genes related to fat metabolism were regulated by PPAR and other signal pathways to improve IMF deposition,and the IMF can break down more fatty acids and volatile flavor substances,and ultimately improve the quality of chicken flavor.Exploring the relationship between the gonadal axis hormone and the quality of flavor meat caused by cock castration will lay a theoretical foundation for the production of highing quality broiler,and provide a new direction of development,which is of great significance to the broiler industry.