Establishment And Optimization Of The Technical System For Population-based Selection In Open Nucleus Breeding System Of Qinchuan Beef Cattle

According to present breeding situation, production practice and real needs in Qinchuan beef cattle breeding, the paper analyzed and established an open nucleus breeding system (ONBS) of Qinchuan beef cattle through population-based selection and breeding, researched on the optimized breeding program in the ONBS according as parameters of population breeding science, biology and economics by adopting approaches of gene flow theory and ZPLAN specific software, studied the expected breeding achievements of the present breeding scheme, revealed the effects of population structure, employment years of bulls and breeding cows, opening level of nucleus population, population sizes and other factors on the comprehensive progress of population-based breeding, the generation intervals and breeding benefits, and worked out an optimized technical indexes for the systematic breeding for the purpose of improving the present breeding scheme.It can be concluded from all the studies here that:(1) It is worthwhile to adopt the population-based selection and breeding for ONBS in order to accelerate the improvement via selective breeding of Qinchuan beef cattle, make up the disadvantages of the closed nucleus breeding system (CNBS), fix the properties, and cultivate excellent individuals. The ONBS of Qinchuan beef cattle consists of three herds of animals in a pyramid-like structure, the nucleus herd on the top, the breeding herd in the middle and the improved herd at the bottom. The nucleus herd is a seed-stock herd composed of prepotent bulls and breeding cows, the breeding herd and the improved herd are individuals coming from the breeding flock and commercial flock, which passed the performance test.(2) In large population size, the maximal genetic progress can be made when the number of cattle in nucleus herd is 10% of the total population of the three groups under normal selection intensity. And the rate of genetic progress can be reached in an ONBS when half of the breeding cows come from fundamental group (the breeding herd together with the improved herd) and the nucleus herd accounts for 5%～10% of the total population.(3) The optimal proportion of breeding cows to be selected from the fundamental group increases parallely with the rise of the selection intensity of bulls but decreases with the increase of the selection intensity of breeding cows. Without confinement of the migratory direction of breeding cows and bulls, the maximal genetic progress can be realized when 50% replacement breeding cows and 5%～20% replacement bull of upper group come from the lower group and 50% replacement bull in lower group come from upper group.(4) The successive migration effects in ONBS usually result in the convergence of the gene frequencies, population means, population differences of subpopulation and total population and increase the homogeneity of total population. Compared with CNBS, ONBS can mitigate the prominent random fluctuation and sampling deviation of hereditary property in population originated from gamete sampling in the replication breeding of small population since ONBS shows special homogeneity effects in migration so maintain genetic homogeneity to total population in a progressive way. The united genetic effects of migration and selection of ONBS are usually advantageous over CNBS in the genetic progress.(5) According to analysis of a herd comprising 2500 breeding cows and within planned 20 years, the present breeding scheme is not in the optimal condition in population size, the proportion of breeding subgroups, utilization of bulls and cows and open level. The present breeding scheme can reach the following results in a calving cycle of each cow: the comprehensive breeding progress of 46.83 CNY, the breeding return of 214.75 CNY, the breeding input of 32.33 CNY, the breeding profit of 182.42 CNY, the generation interval of 5.26 years and the input/output ratio of 1:6.64. Therefore all the parameters can be improved greatly in comparison to international practices.(6) Ideal breeding profit and breeding progress can be made when the proportion of the selected calves is 0.6 and that of selected heifer is 0.8 in breeding program, and these measurements comply with the production practice.(7) It can be concluded from analysis that the ideal service life of the breeding animals in the optimized breeding program is one year of bulls and 5 to 6 years of cows, and one to two years of test bull and 4 to 5 years of test cows all in nucleus herd and breeding herd, and one year of bulls and 6 years of cows in improved herd.(8) The analysis of the optimized breeding program developed in this study showed an increase of the comprehensive breeding progress by 25%, an increase of breeding output by 37%, an increase of breeding profits by 42%, an increase of input/output ratio from 1:6.64 to 1:8.23, and a decrease of the generation interval by 15%, compared with the current breeding scheme.(9) Under the circumstances of limiting the proportion of nucleus herd and with the increase of the breeding population and the number of breeding cattle in nucleus herd, the breeding input (fixed capital) will decrease successively, but the comprehensive breeding progress, the breeding outcome and breeding profit will increase successively.(10) After the comprehensive analysis and optimization of all factors, the comprehensive breeding progress and the breeding profits will remain high in a breeding population of 2500 breeding cows if the proportion of the nucleus herd, the breeding herd and the improved herd is respectively 7%～9%, 11%～13% and 80% and the open level of the nucleus herd is lower than 20%. This study presumes that the ideal breeding profit will be reached if test bulls are in service for one year, the utilization lifespan of other bulls is 3 to 4 years, and this service lifespan of breeding cows is 5 years, all in the nucleus herd, and the ideal breeding profit will be gained if 20%～40% of the cows in improved herd are bred by bulls form nucleus herd. The optimal generation interval will be 4.05 years, the comprehensive breeding progress be 61.72 CNY, the breeding outcome be 306.61 CNY, the breeding profit be 270.83 CNY, reaching increases by 23%, 32%, 43% and 48% respectively in compared with the present breeding scheme. And input/output ratio of the optimized breeding system will be 1:8.56.