Evaluation Of Meat Quality And Optimization Of Selection Schemes For Crossbreeding Quality Chickens

In the last three decades,production of quality chickens has increased rapidly in China and great progress has been made in the field of chicken genetics and breeding. However,with the fast development of quality chicken industry,much more requirements are claimed for the innovation of quality chicken breeding techniques.Aiming at optimizing selection schemes for the quality chicken breeding,this dissertation considers four aspects of quality chicken breeding:evaluation of meat quality,construction of meat quality index,definition of breeding goals,and optimization of selection schemes for specialized lines.The performance data of five commercial quality chicken lines were used to testfy the relevant models developed in this study.The main results and conclusions are as follows:(1) Four representative traits were selected by cluster analysis from eight traits related with meat quality,that is,crude fat content,pH,muscle fiber density and drip loss, and then the meat quality was qualified by using the modified principal component analysis in five quality chicken.The results showed that the meat quality of S01 line was the best,S03 the second,and D99 the worst.Moreover it was found that meat quality of female chickens is higher than that of male chickens in all of the five lines.After getting the sequential data set of meat quality,the meat quality(MQI) was constructed by the linear programming techniques for multidimensional analysis of preference.The MQI not only simplify the qualification of meat quality but also can be brought into the breeding objective as an individual trait performance.(2) Seven objective traits:meat quality,annual egg production,fertilization rate, hatchability,finish weight,feed conversion rate and meat productivity were selected based on actual quality chicken production from three classes traits(meat quality,production and reproduction traits).And then the marginal benefits of production and reproductive traits were deduced by marginal profits principal,but for the meat quality trait,its marginal benefit was calculated based on the hypothesis that MQI obey normal distribution and the MQI of quality distribute within the optimum range,then there is an market price difference between the MQI within the optimum range and the outside.Sensitivity analyses show that changes of trait performance play an important role in the marginal benefit, which decreasing with the performance improvment of traits self-class.The marginal benefit of egg production,fertilization rate(hatchability) increased by 37.9%,18.8% respectively with the egg production decreased by 10%.Some results also show that marginal benefit varied with the different level of market prices.(3) Total 48 crossbreeding systems,including 24 three-way crossbreeding systems and 24 four-way corssbreeding systems were simulated based on four pure lines A,B,C and D. Cost-benefit evaluation analyses show that C×(A×B)♀and(C×D)×(A×B)♀crossbreeding system is the most high in the three-way and four-way corssbreeding systems respectively, and four-way is better than three-way,the cost/profit ratio and the GGP scale/CS scale ratio of three-way is 1.03 and 5.99 times as much as that of four-way,but the average discounted profit and the profit per commercial chicken of four-way is 1.05 times as much as that of three-way.The maginal profits principal combined with systematic analysis was used to evaluate the marginal benefit and breeding importance of objective traits for each line in foue-way crossbreeding system(C×D)×(A×B)♀,the result indicated that the importance of finish weight(35.95%),feed conversion ratio(25.09%) and meat productivity(14.37%) were the most important traits in line C,meat productivity(38.17%), feed conversion ratio(19.51%),egg productivity(15.84%) and finish weight were the most important in line D,MQI(32.05%),egg productivity(19.51%) and feed conversion ratio (15.71%) were the most important in line A,egg productivity(55.95%) and meat productivity(11.32%) were the most important traits in line B.Judging from the whole crossbreeding system,egg productivity of line B is the most important objective traits, finish weight of line C is the second,MQI of line A,and meat productivity of line D is the third and forth respectively.Based on these,the study determined the representative selection traits by simplification of breeding objective.(4) Pure line selection(PLS) and combined crossbred and purebred selection(CCPS) were used to breed the objective traits of each specialized line in four-way crossbreeding system(C×D)×(A×B)♀,the simulated selection experiments show that the hereditability of crossbred performance and the beginning generation scale play an important role in selection efficiency besides the selection method and correlation coefficients of purebred and crossbred phenotype(r_pc).And the slection efficiency of CCPS is higher than that of PLS in general,especially the lower r_pc,however,the relative efficiency of CCPS to PLS with lower r_pc is higher than that of higher r_pc,for example,efficiency of CCPS is 20.01, 10.52 and 4.43 times as much as that of PLS with beginning generation scale ns= 60 and r_pc is equal to 0.2,0.4 and 0.8 respectively in line A,same regularity existing in line B,C and D.Thus we deduced that CCPS could use instead of PLS with the lower r_pc,but CCPS has the disadbantage that would increase the inbreeding speed. PLS-MAS and CCPS was used to select in line A,the genetic gains improved much more relative to PLS vs.CCPS which use phenotype information only in the breeding schemes, meanwhile,inbreeding speed appears to be in control effectively.Based on this we can conclude that the CCPS and MAS could bring additional genetic gains for breeding schemes.