Surrogate rams: An alternative to artificial insemination?

Surrogate rams could provide an alternative to artificial insemination, helping producers reach their sheep breeding goals, such as higher feed efficiency rates and lower environmental impact, more quickly.

This could significantly enhance the efficiency and sustainability of the UK’s sheep production, said Dr Emily Clark, reader and research group leader at the University of Edinburgh’s Roslin Institute.

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“We’re still at the proof-of-concept stage, but the technology could be transformative. We want [to engage in] dialogue with the sector,” Emily said.

Unlike other livestock sectors, artificial insemination (AI) is not used routinely in sheep breeding because of its invasive nature and expense, she elaborated.

This limits genetic gain to what can be achieved through natural mating. Surrogate sires, or “mobile AI units”, provide an alternative way of disseminating high-value genetics by natural mating.

Emily’s work builds on earlier research by an international team, including the Roslin Institute, which showed that animals made infertile by editing the gene NANOS2 can become fertile again after receiving stem cells from donor animals.

Applied to sheep, this technology could be used to speed up genetic gain, with surrogate rams used to produce progeny with the donor ram’s high-value genetics.

“Instead of having one ram disseminating high-value genetics, we would have thousands. And the surrogate sire would not be ‘one size fits all’ – it could be bred for a particular system,” said Emily.

Indirect gene editing

Prof Mike Coffey of Scotland’s Rural College, who joined the conference by video link, added that the process uses gene editing only to stop the surrogate ram producing its own spermatogonial stem cell, so it does not pass on its own genetics.

Asked if the sheep industry was ready for such a move, he said: “Anecdotally, 40,000 rams are traded a year. Are all of those genetically superior for modern traits? No, they are not fit for the future, and our current structure won’t let us get there fast enough.”

Current regulations only permit the use of genome editing in animals for research and development purposes.

Next steps

“In the future, as the regulations for animals are evaluated, the surrogate sires concept may be more acceptable to consumers and policy makers, as no genome-edited product is entering the food chain,” Emily told Farmers Weekly.

“The next steps are to generate a flock of sheep with the NANOS2 gene turned off using genome editing, which will likely take three to four years, and to perfect the spermatogonial stem cell culture and transfer from the donor to the surrogate, which are both difficult to do.”

Emily and Mike are working with Dr Jon Oatley of Washington State University on a potential model for rolling out the technology.

This would involve breeding elite animals in a nucleus unit, which would supply a large multiplier unit for surrogate rams. These would be distributed on a commercial scale.

“I think we’re probably five years from achieving proof of concept and a further five to make [this] model feasible in a commercial setting,” said Emily.

Dr Emily Clark and Prof Mike Coffey were speaking at the recent Sheep Breeders Round Table 2024, held near Derby.