Cloning and genetic improvement of beef cattle

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Abstract
Cloning of cattle from embryos has been achieved by nuclear transfer. Repeated cloning to produce large clones of genetically identical individuals for commercial use may soon become possible. The main advantage in breeding will come from identifying and using superior clones, selected to fit particular husbandry and marketing niches. Two types of cattle clones will be required, terminal clones chosen for economic merit in production traits, such as growth and carcass traits, and maternal clones chosen for reproduction and maternal traits, such as short calving interval, ease of calving, milking and mothering ability and small mature size. Clonal selection and use will provide several steps of improvement. An initial gain will come by recruiting clones from elite stocks and further responses by selecting the best clones for commercial use. This will reverse the normal improvement lag between breeding and commercial stocks. Heterosis will also be exploited by using crossline clones. For continuous genetic improvement, genetic variation will be maintained by breeding the next generation from a number of selected male and female clones and testing and selecting their progeny, the new set of clones, as before. For maximum improvement rates, both male and female clones will need to be tested. In the short term (5 to 10 years), benefits will come from testing a large number of clones by which gains in economic merit of proportionately 0·15 to 0·30 of the mean can be achieved. Further improvements will come by rebreeding the best clones and testing and selecting the new set of clones from which annual genetic response rates of proportionately 0·02 to 0·03 per year are possible. Cloning thus offers considerable advantages in the improvement of beef cattle.