Even the hottest stud can only sire so many offspring. To speed up livestock breeding, biologists have created pigs, goats and mice whose testicles are effectively clones of those of a different male, meaning these animals father that male鈥檚 offspring.
鈥淚t will allow more farmers to get hold of animals with the characteristics they want,鈥� says Bruce Whitelaw at the Roslin Institute in the UK. 鈥淢any people did not think this would work.鈥�
The first step in the process is to create host animals that cannot produce their own sperm. This is done by using the CRISPR gene-editing method to disable a gene called NANOS2.
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Next, sperm-producing stem cells are taken from the testicles of another male and injected into those of the young hosts. When the hosts become sexually mature, they start producing the sperm of the donor male.
The team has done this in pigs, goats and mice, and is working on doing it in bulls. Three host mice have produced 111 offspring by normal mating so far.
The offspring don鈥檛 inherit any DNA from the host, so their nature depends only on that of their genetic parents, says team member Jon Oatley at Washington State University. These parents could be conventionally bred animals or they could be genetically modified in some way. 鈥淭hese surrogates could then be hosts for producing sperm carrying the genetics of a desirable or superior male,鈥� he says.
Such traits might include disease resistance, heat tolerance or improved production of meat or milk, says team member Irina Polejaeva at Utah State University.
Artificial insemination is already used to pass on desirable traits. But skilled personnel and special equipment are needed for every single insemination, and it is only widely used in dairy farming, says Whitelaw.
By contrast, once these 鈥�surrogate sires鈥� have been created, they breed normally. They could be loaned or sold to any livestock farmer.
The team hopes the technique will allow poorer farmers to improve their livestock. Oatley says he has already been talking to non-profit organisations in India and Kenya about ways to do this.
In the meantime, the surrogate sire technique still needs refinement. For instance, sperm production is much lower in the hosts than in normal males.
In theory, this technique could also help save endangered species. For instance, it might have allowed Sudan, the last male northern white rhino, to continue to sire offspring after his death in 2018.
Sperm stem cell transplantation is also being developed as a way of treating infertility in people. For example, some cancer treatments cause infertility. It might one day be possible to restore fertility by removing sperm stem cells before treatment and then reimplanting them in the same individual afterwards.
One problem is that it has proved difficult to isolate human sperm stem cells. However, in July, one team reported having developed a reliable method.
PNAS
