Study On Crossbreeding Effect Of High Quality Chickens And Gene Expression Levels Related With Breast Muscle Development In Different Hybridzed Combinations

Nowadays,for enhancing the production performance and economic benefits,the basic work of domestic poultry breeding concentrates on strain breeding,and obtaining an optimal hybridized combination by crossbreeding.As the most important tissue in the poultry production,skeletal muscle directly affects the production performance and economic benefits.Therefore,the application of hybridized methods to acquire different matching combinations,and screening most optimal hybrid combination by precisely analyzing the production performance of each combination are indispensable for the development of poultry breeding industry.To provide scientific reference and theoretical basis for the breeding of quality broiler chickens,this experiment was implemented to explore the inherited rules of muscle development mechanism and the improvement efficacy of offspring through matching crossbreeding between different strains of Qiling grass chicken.Experiment one:Research on the fitting of growth curves of different quality chicken strainsThe purpose of this experiment is to explore the optimal growth curve fitting model for each strain of Qiling grass chicken.In the experiment,1-day-old chickens of strain 811（n=120,60♂+60♀）,strain 812（n=120,60♂+60♀）,and strain 805（n=120,60♂+60♀）of Qiling grass chicken were selected.They were raised in separate cages under the same breeding environment,and freely access to the feeds and water.The normal immunization procedures were carried out.At 0,2,4,6,8,10,and 12 weeks of age,all animals were weighed after 12 hours fasting.The results showed that among these three fitting models,the R²of the Von Bertalanffy model of strain 811（male and female）was consistent with the Gompertz model,but the E value of the Von Bertalanffy model was smallest;all fitting models of strain 812 was generally consistent,but the E value of the Gompertz model was smallest;The R²of Von Bertalanffy model of both male and female chickens in strain 805were 0.999,which was higher than other models.In addition,the weight estimates of Von Bertalanffy model for strain 811 and strain 805 were closer to the actual observed values,While the Gompertz model had the best effect on the weight estimation of strain 812.Thus,the Von Bertalanffy model is more suitable for the growth curve fitting of strain 811 and strain 805,whereas the Gompertz model is suitable for strain 812.Experiment two:Comparison of growth performance and slaughter performance on different hybridized combinationsThe aim of this experiment is to screen out the best hybrid combination by comparing and analyzing the growth performance and slaughter performance of different matching combinations of Qiling grass chicken.This experiment totally comprised 3 pure-breeding combinations,3 two-line hybridized combinations,and 2 three-line hybridized combinations.150 qualified eggs of each combination were selected to hatch in same batch for 21 days,120 healthy chicks（male♂and female♀equivalent）in each combination were selected.Each chick was raised for 13 weeks in separate cages under the same breeding environment,and freely access to the feeds and water.All animals were weighed for every2 weeks during experimental period,and at the end of 13^thweek,8 males and females of each combination were selected for slaughter determination according to the average weight.The results showed that the average weight of three-line hybridized combinations was significantly higher than that of two-line hybridized combinations at 2-12 weeks（P<0.05）;In the two-line hybrids,the weight of ZX matching combination was significantly higher than that of XZ matching combination during 2-12 weeks（P<0.05）,and the weight of the ZX matching combination was significantly higher than that of the XD hybrids during 2-6 weeks（P<0.05）;In the three-line hybridized combinations,the average weight of male chicken in XZD hybridized combination was significantly higher than that of the ZXD group from 0 to 4 weeks of age（P<0.05）,and the average body weight of female chicken in XZD was significantly higher than that of ZXD hybrids at 0-6weeks（P<0.05）.Additionally,the breast muscle rate and leg muscle rate of pure-bred combination ZZ were lowest（P<0.05）.While these 2 indicators in three-line hybridized chicken were higher than other hybrids（P<0.05）.And the heterosis rates of all indicators in the ZX hybrids were positive.To summarize,the three-line hybridized combination XZD maintains the best hybridization effect for each performance,and the ZX combination has the largest hybrid advantage.Experiment three:Comparison of genes related with breast muscle development expressed in different hybridized combinationsThis experiment was designed to explore the performance and gene expression levels of breast muscle development in offspring of different hybridized combinations.In this experiment,all samples were collected and measured after experimental animals were slaughter as details mentioned in Experimental two.The results showed that for the characteristics of the muscle fibers,the diameter of the muscle fibers of the male chicken in ZZ purebreds was significantly smaller and the density was significantly greater than that of other combinations（P<0.05）.In general,the diameter of the muscle fiber in ZX combination was significantly smaller and the density of muscle fiber was significantly greater than those of other combinations（P<0.05）.For the serum protein analysis,the protein metabolism level of ZZ and ZX were comparatively higher（P<0.05）.The secretion levels of IGF-1,T3 and T4 in the ZZ combination were significantly lower（P<0.05）,whereas those of ZX hybrid were significantly higher（P<0.05）.The skeletal muscle development-related genes（IGF-1R,IGF-2R,Myo G,AKT,Atrogin-1）expression levels in the breast muscles of ZZ and ZX were significantly higher（P<0.05）.In addition,the expression levels of PAX-7,MSTN and Myod in breast muscle of ZZ were significantly higher（P<0.05）,while the expression levels of Mu RF1 in ZX breast muscle were significantly higher（P<0.05）.Taken together,both the pure-breeding combination ZZ and the hybridized combination ZX have strong capacity of protein metabolism and higher levels of skeletal muscle gene regulation,and the ZX and male of ZZ has good muscle fiber characteristics,indicating a good paternal effect of ZZ.All in all,the three-strain matching combination XZD has the best hybridization effect,and the ZX group has the best heterosis.