الملخص الإنجليزي
A variety of options are available for improved performance including altering genotype with genetic improvement of indigenous breeds through selective breeding, upgrading through crossbreeding of indigenous females with semen from genetically superior exotic males with a passible goal of developing a new breed, and introduction of new breeds through transfer of embryos from genetically superior exact breeds at to indigenous females or importation of exotic animals of the desired breeding. Each option has its advantages and disadvantages. The most rapid gains might be possible through importation of exotic breeds. but this is expensive, Sometimes limited by health regulations, and adaptation to the new environment can be a problem In the interest of adaption and survival, systems that utilize the maternal influences of indigenous females are advantageous. In consideration of these maternal influences along with rate of improvement and potential for extensive improvement, both crossbreeding programs that use semen from genetically superior exotic males and those that involve transfer of genetically superior embryos from exotic breeds have their unique merits. Heat stress, because of its negative impact on intensity of oestrus, embryo survival and neonatal survival will affect management of any option chosen for genetic improvement but should be of less concern n programs that utilize indigenous females.
