Development could speed spread of desirable livestock characteristics and improve food production.

September 15, 2020

6 Min Read
Washington State surrogate goat.jpg
One of the "surrogate sire" goats on the Washington State University-Pullman campus.Washington State University

For the first time, scientists have created pigs, goats and cattle that can serve as viable “surrogate sires” — male animals that produce sperm carrying only the genetic traits of donor animals, according to announcements from Washington State University and The Roslin Institute in the U.K.

The advance, published Sept. 14 in Proceedings of the National Academy of Sciences, could speed the spread of desirable characteristics in livestock and improve food production for a growing global population, Washington State said. It also would provide breeders in remote regions with better access to genetic material of elite animals from other parts of the world and allow more precision breeding in animals such as goats where using artificial insemination is difficult.

“With this technology, we can get better dissemination of desirable traits and improve the efficiency of food production. This can have a major impact on addressing food insecurity around the world,” said Jon Oatley, a reproductive biologist with Washington State's College of Veterinary Medicine. “If we can tackle this genetically, then that means less water, less feed and fewer antibiotics we have to put into the animals.”

Oatley's research team used the gene editing tool CRISPR-Cas9 to knock out a gene specific to male fertility in the animal embryos that would be raised to become surrogate sires, Washington State said.

The male animals were born sterile but began producing sperm after researchers transplanted stem cells from donor animals into their testes. The sperm the surrogate sires produced held only the genetic material of the selected donor animals, the researchers said.

They added that the gene editing process employed in this study seeks to bring about changes within an animal species that could occur naturally, such as infertility.

The study is the result of six years of collaborative work among researchers at Washington State, Utah State University, the University of Maryland and The Roslin Institute.

The researchers used CRISPR-Cas9 to produce mice, pigs, goats and cattle that lacked a gene called NANOS2, which is specific to male fertility. The male animals grew up sterile but otherwise healthy, so when they received transplanted sperm-producing stem cells from other animals, they started producing sperm derived from the donor’s cells, the researchers said.

The surrogate sires were confirmed to have active donor sperm. The surrogate mice fathered healthy offspring that carried the genes of the donor mice. The larger animals have not been bred yet, as Oatley’s lab is refining the stem cell transplantation process before taking that next step.

This study provides a powerful proof of concept, Roslin professor Bruce Whitelaw said, adding, “This shows the world that this technology is real. It can be used. We now have to go in and work out how best to use it productively to help feed our growing population.”

Latest step in animal husbandry

Scientists have been searching for a way to create surrogate sires for decades to overcome the limitations of selective breeding and artificial insemination -- tools that require either animal proximity or strict control of their movement and, in many cases, both.

Artificial insemination is common in dairy cattle, which are often confined so their reproductive behavior is relatively easy to control, but the procedure is rarely used with beef cattle that are allowed to roam freely to feed. For pigs, the procedure still requires the animals be nearby because pig sperm does not survive freezing well. In goats, artificial insemination is quite challenging and could require a surgical procedure, the researchers said.

The surrogate sire technology could solve those problems, since the surrogates deliver donor genetic material through normal reproduction, which would enable ranchers and herders to let their animals interact normally on the range or field, the researchers explained. Donors and surrogates would not need to be near each other, since either frozen donor sperm or the surrogate animal itself can be shipped to different places.

In addition, female NANOS2 knockout animals remain fertile — the gene only affects male fertility — and could be bred to efficiently generate sterile males to be used as surrogate sires, the researchers added.

The Roslin Institute noted that the study also shows that it is possible to sterilize cattle by using genome editing on the NANOS2 gene.

This technology has great potential to help food supply in places in the developing world where herders still have to rely on selective breeding to improve their stock, Utah State University professor Irina Polejaeva said.

“Goats are the number-one source of protein in a lot of developing countries,” Polejaeva said. “This technology could allow faster dissemination of specific traits in goats, whether it’s disease resistance, greater heat tolerance or better meat quality.”

The surrogate sire technology could also open up a new option for genetic conservation of endangered species, whose dwindling numbers leave animal communities isolated from each other, limiting their genetic diversity.

"Genetic improvement of livestock, implemented through application of advanced breeding technologies such as artificial insemination, has been hugely successful in advanced economies. In our study, we used gene editing technology to develop male surrogates that do not produce their own sperm but can act as incubators for the sperm of other males. This development has potential application for genetic improvement of livestock in low- and middle-income countries, such as those with whom the Centre for Tropical Livestock Genetics & Health works, where smallholder livestock holdings are crucial for food security, nutrition and income generation," Roslin research fellow Dr. Simon Lillico said.

Perception and policy hurdles

None of the benefits of surrogate sires can be realized, however, without changes in the current landscape of government regulations and public perception, Washington State said.

Even when the technology is advanced enough for commercialization, gene-edited surrogate sires could not be used in the food chain anywhere in the world under current regulations, even though their offspring would not be gene edited. This is due, in part, to misperceptions that gene editing is the same as the controversial gene manipulation, Oatley said. Gene editing involves making changes within a species that could occur naturally; it does not combine DNA from different species.

Oatley said he realizes that there is a lot of work to do outside of the lab and recently joined the National Task Force on Gene Editing in Livestock to bring together researchers, industry representatives, bioethicists and policy-makers to find a path forward for the technology.

“Even if all science is finished, the speed at which this can be put into action in livestock production anywhere in the world is going to be influenced by societal acceptance and federal policy,” Oatley said. “By working with policy-makers and the public, we can help to provide information assuring the public that this science does not carry the risks that other methods do.”

This study was supported by the U.S. Department of Agriculture's National Institute of Food & Agriculture, Washington State University's Functional Genomics Initiative and Genus PLC. The Roslin Institute receives strategic investment funding from the Biotechnology & Biological Sciences Research Council as part of U.K. Research & Innovation, and it is part of the University of Edinburgh’s Royal (Dick) School of Veterinary Studies. At Utah State University, this study was supported by the Utah Agricultural Experiment Station.

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