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Many of the benefits from the use of advanced reproduction technologies (ART) flow from their ability to produce more progeny per individual parent. This can allow breeding schemes that produce more rapid genetic gain in the breeding nucleus, and rapid dissemination of superior genetics from the nucleus to production herds and flocks. With the most widely used technique, artificial insemination (AI), males can be used across large numbers of females, in more compact joining periods than would otherwise be possible, and across farms, regions or countries. There is limited scope to increase the number of progeny from females using embryo transfer (ET) and multiple ovulation embryo transfer (MOET). However, ET and MOET have facilitated genetic dissemination across the world by enabling the transport of embryos rather than live animals between countries of differing disease status. ET, MOET and embryo cryopreservation have been available for use in cattle for over 25 years, and AI since the 1950's. ... The principles by which the effect of these technologies on livestock improvement can be evaluated were included in the review of van Arendonk and Bijma (2002). The objective of this paper is to review recent progress in emerging reproductive technologies, and to discuss some implications of these technologies on livestock breeding and production. In particular, we will discuss progress in germ cell transfer in males (testes transfer) and females (oocyte transfer), and prospects for in vitro gametogenesis (IVG) for both sexes. All of these offer potential to reduce the generation interval. The rate of genetic change due to selection will depend on measurement of phenotypes in relation to reproductive age, and this relationship will be explored in detail in this study. As noted by van Arendonk and Bijma (2002), reducing the generation interval in a breeding nucleus of fixed size may be at the expense of increasing the rate of inbreeding, so potential uses of these technologies outside nucleus populations are discussed. |
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