The Effects Of Improvac Immunocastration On The Development Of Muscle Fibers In Male Broiler Chickens

GnRH hormone immunoneutralizing technology is an immuno-castration method that complies with animal welfare.It is currently an important method for immuno-castration of pigs and control of meat quality.In the early stage,we used Improvac to immuno-castrated roosters.It has a significant inhibitory effect on the secretion of testosterone and the development of spermatozoa in the testis,but it has not been reported in the literature whether Improvac has been inoculated on the muscle development of broiler chickens.The purpose of this study was to evaluate the impacts of Improvac on the size and type of muscle fibers in the pectoral and thigh muscles of male broiler chickens,as well as the impacts of Improvac on the expression levels of genes related to muscle fiber types and muscle fiber development.We also hope to lay the foundation for exploring the feasibility of Improvac used in the immuno-castration of roosters.Fifty 2-week-old male Tianfu broilers（TF02）were randomly divided into four groups.The control group（n=15）was injected with 0.6 ml of normal saline at the 3^rdand 6^thweek old;the early-immunocastrated group（n=15）was injected with 0.6ml Improvac and0.6ml saline at the 3^rdand 6^thweek respectively;the late immunocastrated group（n=10）was injected with 0.6ml saline and 0.6ml Improvac at the 3^rdand 6^thweek old respctively;the early+late immunoastrated group（n=10）was injected with 0.6ml Improvac at the 3^rdand 6^thweek old respectively,and then pectoral and thigh muscles were collected at the 5^th,9^thand 14^thweek old to measure the physicochemical properties,cross-sectional area size and fiber type of muscles,as well as the expression levels of genes related to muscle fiber type and muscle development.The results showed that:（1）In the pectoral and thigh muscles of 5^th,9^thand 14^thweek old,the value of p H₄₅and PH₃₀₀,L*,a*,b*,and chroma（C*）and hue angle（h°）in Improvac-treated groups（early-immunocastrated group,late-immunocastrated group and early+late-immunocastrated group）are not significantly different from the control group（P>0.05）;（2）In the pectoral muscles at 5^th,9^thand 14^thweek old,there was no significant difference in the cross-sectional area（CSA）and fiber density between the control group and the Improvac-treated groups（P>0.05）.In thigh muscles at 5^thand 9^thweek old,there was no significant difference in CSA and fiber density between the control group and the Improvac-treated groups（P>0.05）,while at the 14^thweek old,the early-immunocastrated group had significantly larger CSA than the control group（P<0.01）.No difference was found in fiber density（P>0.05）;（3）In the pectoral muscles,the relative expression levels of Myo D,Myf5 and MSTN were not significantly different among all the groups at 5,9 and 14 weeks of age（P>0.05）.In the thigh muscles,the relative expression level of MSTN in the late group was significantly lower than that in the early group at 9 weeks of age（P<0.05）.At 5 and 14weeks of age,the relative expression levels of Myo D,Myf5 and MSTN were not significantly different among all the groups（P>0.05）.（4）The pectoral muscle fibers of 5,9 and 14 weeks old were all identified as fast muscles,while the thigh muscle muscle fibers were all composite fibers,but Improvac treatment did not change the ratio of fast and slow muscles（P>0.05）;（5）The relative expression levels of SM1,MYH1B,and MYH1F in the pectoral muscles of individuals at 5,9,and 14 weeks of age have no difference among all the groups（P>0.05）.In the thigh muscles,at 5 weeks of age,the relative expression level of MYH1B in the control group was significantly lower than that of the early group（P<0.05）;at 9 weeks of age,the expression level of SM1 in the control group was significantly higher than that of the early and late groups（P<0.05）;At 14 weeks of age,the relative expression levels of MYH1B,MYH1F,and SM1 did not differ significantly among groups（P>0.05）.In conclusion,early treatment of Improvac affects the fiber size and the expression of muscle fiber type and development related genes while early,late,and early+late treatments of Improvac have no effect on the p H,meat color,muscle fiber size,muscle fiber type,and expression of muscle fiber type and muscle development-related genes in the pectoral muscles.