Study On The Difference In Egg Quality Between Yun Nong Chicken And Jing Fen Chicken Based On RNA-Seq

Egg quality is one of the most important economic traits in the poultry industry,directly related to the quality of chicken products,breeding efficiency,and consumer health.Eggshell quality is an important trait in egg quality,and its quality not only affects the transportation,storage,and price of eggs,but also affects the hatchability of fertile eggs,making it an important research direction in poultry breeding and production.Yunnong chicken(YN)is a local genetic resource recently discovered in the border area of Yunnan Province.Previous studies have found that it not only has good egg-laying performance,but also excellent egg quality,especially with regard to eggshell glossiness.Jingfen chicken(JF)are currently one of the most commonly raised commercial egg-laying chicken breeds on the market.In order to systematically study the differences in egg quality,especially eggshell characteristics,between YN and JF eggs,this study randomly selected 200 YN and 200 JF hens,totaling 400 chickens,raised under the same feeding conditions and nutritional levels until they were 300 days old.Sixty eggs from each breed were collected for egg quality testing,including longitudinal and transverse diameters,egg weight,egg shape index,eggshell thickness,eggshell strength,albumen height,yolk color,Haugh unit,yolk weight,and eggshell weight.At the same time,scanning electron microscopy was used to compare and analyze the cross-sections and internal mammillary structures of YN and JF eggshells.In order to screen for functional genes that may affect YN eggshell quality,uterus and kidney tissues were collected from YN and JF chickens for transcriptome sequencing,and differentially expressed genes and signaling pathways related to eggshell characteristics were identified and validated by RT-q PCR.The main results are as follows:(1)Comparison of egg quality: At 300 days of age,the longitudinal and transverse diameters of eggs from Yunnong chickens were significantly smaller than those from Jingfen chickens(P<0.01),but there was no significant difference in egg shape index(P>0.05).Yunnong chicken eggs had significantly higher shell strength and thickness than Jingfen chicken eggs(P<0.01).The egg weight and shell weight of Yunnong chicken eggs were significantly lower than those of Jingfen chicken eggs(P < 0.01).The yolk weight and yolk color of Yunnong chicken eggs were significantly higher than those of Jingfen chicken eggs(P < 0.01).The albumen height and Haugh unit of Yunnong chicken eggs were higher than those of Jingfen chicken eggs,but the differences were not significant(P>0.05).(2)Correlation between different indicators of egg quality: There is a highly significant positive correlation(P<0.01)between the following: egg transverse diameter and yolk color;egg shape index and shell strength;egg shape index and shell thickness;egg shape index and albumen height;egg shape index and Haugh unit;shell strength and shell thickness;shell strength and albumen height;shell strength and Haugh unit;shell thickness and albumen height;shell thickness and Haugh unit;albumen height and Haugh unit.The correlation coefficients are 0.473,0.917,0.928,0.977,0.935,0.864,0.951,0.909,0.946,0.931,and 0.972,respectively.(3)Eggshell ultrastructure: Scanning electron microscopy observations showed that the shell thickness,mammillary density,and effective layer thickness of Yunnong chicken eggs were significantly higher than those of Jingfen chicken(P<0.01),while the mammillary layer thickness of Yunnong chicken eggs was significantly lower than that of Jingfen chicken(P<0.01).(4)Transcriptome sequencing analysis: In the uterine tissue,102 differentially expressed genes were identified between Yunong chickens and Jingfen chickens,including 56 upregulated genes and 46 downregulated genes.In the kidney tissue,393 differentially expressed genes were identified between Yunong chickens and Jingfen chickens,including 195 upregulated genes and 198 downregulated genes.Based on the KEGG and GO enrichment results,genes such as LSS,NSDHL,MSMO1,SQLE,FDFT1 were selected,which are involved in the signaling pathways related to vitamin D3 metabolism.Therefore,these genes are considered as candidate genes that may affect eggshell traits.(5)In RT-q PCR validation: In the uterus tissue,the expression levels of LSS,MSMO1,SQLE,and FDFTI genes in Yunnong chickens were extremely significantly higher than those in Jingfen chickens(P<0.01),and the expression level of NSDHL gene was significantly higher than that in Jingfen chickens(P<0.05).In the kidney tissue,the expression level of FDFT1 gene in Yunnong chickens was extremely significantly higher than that in Jingfen chickens(P<0.01),and the expression levels of LSS and SQLE genes were significantly higher than those in Jingfen chickens(P<0.05).In summary,Yunong chickens have better eggshell strength and thickness than Jingfen chickens,which can effectively reduce the eggshell breakage rate.This provides important reference value for the selection and breeding of eggshell traits in commercial laying hens,and provides a scientific theoretical basis for the molecular mechanism research on eggshell quality differences.It also promotes the protection and development of Yunong chickens,a high-quality local chicken resource in Yunnan.