Study On The Sternal Ossification Of Meat Ducks And Its Relationship With Breast Muscle Development

Breast muscle weight and percentage are important economic traits in meat duck production.Muscle development is closely related to sternal development,and sternal ossification is an important feature of sternal development.So far,there are very limited studies on the sternal ossification process and the relationship between sternal ossification and breast muscle development of duck.Therefore,this study aim to explore the sternal ossification pattern of meat duck and its relationship with breast muscle development through morphology and histology observation,phenotype measurement and detection of key genes expression levels during 5~9 weeks old.The main results are as follows:(1)The results of morphological observation and alixin blue-alizarin red staining showed that: Both sternal body and carina sterni began to be ossified at 5~6 weeks old and were basically ossified at 9 weeks old.Tergonta began to be ossified at 6~7 weeks old and was not fully ossified at 9 weeks old.The ossification of sternal body was began at intercostal notch on both sides,then developed to carina sterni,and finally completed from front end to back end.The ossification of carina sterni was occur from bottom to top.And the ossification order of tergonta was from near end to far end.From the histological sections,alixin blue staining and HE staining,we found that bone cell types have changed during the course of sternal ossificatio,and bone marrow cavity and its internal blood cells also appeared.(2)The measurement results of ossification phenotype indexs indicated that: The cartilage of sternal body was mainly ossified during 5~7 weeks old,while at 7 weeks old sternal body cartilage length was only 2.05 cm and sternal body cartilage length/carina sterni length was only 16.36%.The cartilage of tergonta was continuous happened during6~9 weeks old,while at 9 weeks old tergonta cartilage length and tergonta cartilage length/tergonta length were 0.71 cm and 12.49%,respectively.Besides,four ossification phenotypes indexs were significantly higher in male ducks than in female ducks at the same week(P<0.05).(3)The results of phenotype indexs measurement and correlation analysis showed that:Breast muscle weight and percentage and five sternal growth phenotype indexs allsignificantly increased during 5~8 weeks old(P<0.05),but not significantly changed between 8 and 9 weeks old.During 5~9 weeks old,breast muscle weight was significantly correlated with the all seven sternal growth phenotype indexs(P<0.01,r=0.17~0.68),including carina sterni depth,carina sterni length,distance between cranial lateral process,distance between tergonta,bevel length of notch,vertical length of notch and length of central lateral process.At 5 weeks old,breast muscle percentage was significantly correlated with distance between cranial lateral process(P<0.01,r=0.27).At 5 and 6 weeks old,breast muscle percentage was significantly correlated with distance between tergonta,bevel length of notch,vertical length of notch and carina sterni depth(P<0.01,r=0.17~0.56).At 5 and 8 weeks old,breast muscle percentage was significantly correlated with carina sterni length(P<0.01,r=0.30?0.20).In terms of ossification phenotype indexs,breast muscle weight was significantly correlated with tergonta cartilage length at 8 and 9weeks old(P<0.01,r=0.37?0.34)and with sternal body cartilage length at 8 weeks old(P<0.01,r=0.33),while breast muscle percentage was significantly correlated with sternal body cartilage length at 8 weeks(P<0.01,r=0.33).(4)The results of quantitative real-time PCR analysis revealed that: Cartilage ossification-realted genes COL2A1,COMP and COL10A1 were specific highly expressed in sternal cartilage.Them relative expression levels peaked at 5,6 and 7 weeks old,respectively,significantly higher than those of other weeks(P<0.05).COL1A2,CTSK and SPARC genes were expressed in both sternal cartilage and bone.In sternal cartilage,the relative expression levels of COL1A2 and CTSK genes peaked at 8 weeks old,and SPARC gene peaked at 7 weeks old.In sternal bone,the relative expression levels of COL1A2 and SPARC genes were not significantly changed during 7~9 weeks old,but CTSK gene peaked at 7 weeks old.In addition,the relative expression levels of MMP13 gene were stable and no significant differences was detected.In summary,this study has revealed the basic rules of sternal ossification process in the growth and development of meat duck sternum,has found that breast muscle development is related to sternal ossification process,and has screened key genes which affect sternal ossification.These results have some reference value to studies on the developmental law,regulation mechanism,and indirect selection of meat duck breastmuscle.