A research on the development of meat type dam and sire quail lines using multi trait mixed model equations

Poultry breeding programs are aimed to improve the genetic potential of animals through selection and crossbreeding plans. Highly selected elite sire and dam purelines form the basis of today‟s broiler breeding programs. Commercial broilers are obtained from three-way or four-way crosses of specific closed purebreeding lines. Initially, realized genetic parameters in the selection experiments were used in estimation of heritabilities and genetic correlations. Currently, the application of mixed model methodology (leading to the best linear unbiased prediction of genetic effects), which requires the knowledge of variance components (direct additive genetic variance and residual variance for the simplest animal model), is the method of choice. Genetic improvement of sire and dam lines has given poultry geneticists the opportunity to take advantage of various traits in different parental lines. The selection programs in commercial broiler companies are based on multiple selection methods for different traits, such as growth rate, feed efficiency, and reproduction traits. Despite their small body size, Japanese quail have an important role in commercial production because of having high egg and meat production capacity. Much of the genetic improvement studies on quail have focused on early egg number or body weight at fixed ages in which the phenotypic mass selection is considered. Information on quail lines selected for meat or egg production is extensive but the data on heterosis in quail are rare. Contrary to commercial broiler production, crossbreeding of highly selected lines have been rather little use in quail production. The present study in Japanese quail was aimed to develop multi-trait genetic selection programs for meat type dam and sire lines utilizing the mixed-model methodology. In total, 5000 pedigreed quail were formed the basis of the research where a multi-trait animal model was performed for the first time in a selection study of quail. Two pedigreed initial flocks were achieved by randombred and non-selected quail flocks obtained from different research centers of Turkey. Then, two flocks consisting of a total of 320 families (320 male- 960 female) were developed from the initial flocks, so as to obtain a selection flock dam line (SFDL-1) and a selection flock sire line (SFSL-1). Body weight at 5 weeks of age (BW) was chosen as a primary selection criterion in both flocks. The total egg number (EN) from the day of first lay to the 20 weeks of age, relative growth rate (RGR) at 5 weeks of age derived from Gompertz equation, and fertility rate (FR) were used as selection criteria in SFDL. In SFSL, age at point of inflection (IPA) derived from Gompertz growth curve, feed conversion ratio (FCR) between 3 to 5 weeks of age, and carcass yield (CY) at 5 weeks of age were determined as selection criteria. Multi-trait BLUP methodology was carried out separately for each line in genetic improvement of birds. Within each flock, 25 percent of males and females with highest breeding value were selected to produce next generations (SFDL-2 and SFSL-2). Genetic parameter estimates, realized genetic parameters, selection responses, and genetic trends were obtained for both flock. Heritabilities of BW, EN, RGR and FR traits were estimated ranging from moderate to high in SFDL-1, and from low to moderate in SFDL-2. Heritabilities of BW, IPA, FCR, and CY traits in SFSL-1 were estimated as 0,36, 0,20, 0,14, and 0,55 while the parameters in SFSL-2 were estimated to be 0,23, 0,21, 0,13, and 0,53, respectively. Significant (P <0,01) improvements for means of BW, EN, RGR in SFDL, and BW, IPA, FCR, CY traits on generations in both flocks were observed. The results of the study revealed that the negative genetic relationships exhibited between some studied traits were overcomed by modern poultry breeding methods such as selection via multi-trait BLUP. The more accurate genetic evaluation can be performed by multi-trait BLUP which uses all available information from several correlated traits as well as records of all relatives than other alternatives.