Embryo Transfer. Credit, BBC.
Embryo transfer (ET) refers to the process of assisted reproduction when embryos are placed into the uterus of a female with the intention of establishing a pregnancy. The process can involve a number of different steps and technologies, but generally requires two main components: generating and then obtaining (flushing) the embryos from the donor female and transferring each embryo into a different female (surrogate). ET is used to exploit the genetics of the female in the same way that frozen semen is used to exploit the genetics of the male. Advances in embryo technology are extremely useful in species such as cattle and buffalo which typically produce less than 1 calf per year. Comparatively, with embryo transfer, 9-12 calves can be produced per year.[1]
The first calf produced experimentally through ET was born in 1951, but it took until the 1970’s for the first calf to be commercially produced in the UK. The commercial ET industry was developed in North America in the early 1970’s with the introduction of exotic European breeds of cattle. As ET technology developed and improved, embryo transplant became more commonplace and affordable. Primarily, ET is used for genetic improvement rather than for increasing the numbers of a particular breed or phenotype.[2]
Identical twins as a result of embryo splitting.
There are two procedures presently available for production of embryos from donor females: 1) superovulation, followed by artificial insemination and then flushing the uterus to gather embryos; and 2) in vitro fertilisation (IVF) consists of the recovery of eggs from the ovaries of the female then maturing and fertilising them outside the body until they are ready for implantation in foster females.
Although this technology is not commercially available in developing countries, ET technology could provide opportunities for the conservation and the development of minor breeds.[3] ET research and genetic improvement of local breeds could be made available to smallholder farmers in developing countries, through National Agriculture Research Centres, provided the expertise and infrastructure are available. For example, researchers at the International Livestock Research Institute (ILRI) based in Nairobi, Kenya succeeded in breeding their first calf through in vitro embryo production (IVEP) in 2009.[4] The East Africa Semen and Embryo Transfer Association, with support from the World Bank East African Agricultural Productivity Project (EAAPP) offers a minimum ET package including the harvesting of embryos from 3 donors and a transfer to at least 5 surrogates for Ksh 200,000 (nearly US$2,000), prohibitively expensive for most livestock producers.[5]
Contribution to Sustainable IntensificationEmbryo transfer has a number of distinct advantages: by using laboratory equipment it reduces pressure on natural resources used during a natural breeding process; cattle genotypes and production environments can be matched more closely; and it theoretically could allow farmers to more efficiently use their herd by renting their best cows as donors and utilise their lower-quality ones as surrogates.[6] Although embryo production and transfer may not have dramatic effects on rates of genetic gain, it can have considerable increases in efficiency. Heifer replacement programmes take a long time, maintaining a large number of males can be costly and the commercial relevance of some breeds may decline. If ET became a routine operation through artificial insemination, for example, beef operations based on this system could become competitive with pig and poultry production in terms of efficiency of food utilisation.[7]
Developing countries face a number of challenges to establishing successful animal breeding programmes such as inadequate infrastructure for performance testing due to small and varied herd sizes, communal grazing often interferes with implementing animal health programmes, and poor nutrition, especially in cattle, which leads to low reproductive efficiency. [8] As the selection of the donor female is one of the most important components in successfully applying embryo transfer (ET), improved cattle nutrition is a fundamental prerequisite.[9] Highly experienced and trained staff, and capital investment in adequate facilities, equipment and drugs are also necessary. [10]
The principal benefit of embryo transfer (ET) is the possibility to produce several offspring from a female, just as artificial insemination produces many offspring from the same male. The potential for reproduction in cattle is enormous – each female calf is born with an estimated 150,000 eggs. Yet, the average reproductive rate of a cow is around 1 calf per year, producing around 8-10 calves during a lifespan.[11] With ET, the average reproduction of a cow can be increased ten-fold in a given year and five-fold or higher per lifetime.[12] Increasing the reproductive rate of selected females also means that genetically outstanding animals can contribute more to breeding programmes.[13]
Drought is a major risk for livestock morbidity and a recurring challenge to maintaining herd size particularly in dryland areas in developing countries. In developed countries, some livestock keepers are using embryo transfer (ET) as a means of risk management against drought or other disasters that may significantly reduce herd size. By placing embryos into ET programmes and freezing them for use in the event of a drought, this allows for regenerating stock of superior quality rapidly. This method may also be less expensive than repurchasing cattle. Further, less meritable but nonetheless reproductively sound females from the surviving herd can be used as surrogates.[14] Although this strategy for risk management remains unavailable to most in developing countries, if ET technology becomes cheaper and more accessible to smallholders, it could become part of a suite of solutions to improve resilience to drought, climate change and other factors affecting livestock mortality rates.
Transport of embryos is much cheaper than live animals. However, cost is still a prohibitive factor in the uptake of embryo transfer (ET) technology, both in developed and developing countries. In North America and Europe, about 1 out of 500 calves born throughout the 1980’s was from embryo transfer[15] but this has increased significantly – more than 1 million bovine embryos were made available globally for transfer in 2013.[16] Based on the latest available data, less than 2% of all embryo transfers occurred in Africa.[17] Equipment and supplies tend to be more expensive to acquire in developing countries due to transportation costs, import tariffs, and limited access to finance.[18] In addition to capital investment, one of the greatest costs to an ET programme are the surrogates as they need to be in the same stage of the estrous cycle of the donor, which can be challenging to synchronize, and costly if not managed properly.[19]
In vitro fertilization (IVF) of the embryos, however, can lower costs of an ET programme as it facilitates the recovery of a large number of embryos from a single female, reducing the cost per embryo and improving economies of scale for larger programmes.[20] ET technologies can also be adapted to local conditions to manage costs. For example, dry ice and alcohol baths are just as effective as more advanced freezing techniques, and these are also less labour intensive processes. Similarly, equipment such as filters, disposable syringes and plastic dishes are not essential for isolating embryos, suggesting that innovation in the field is possible, but more applied research is needed.[21]
Value addition can be gained through demand for embryo transfer (ET). For example, farmers keeping indigenous or inferior quality breeds, but of adequate reproductive capacity, can rent their cows for use as surrogates. Alternatively, farmers keeping superior breeds can sell their 100-150 ova per cow per month. This strategy can be used to improve household income and increase the attractiveness of farming, as has been demonstrated in Brazil with hope for application in Kenya.[22]
