Scientists Genetically Edit Mice To Have Female Only Litters With 100 Percent Efficiency

Scientists have genetically edited mice so they only give birth to litters of all male or female offspring. Tests showed the technology was 100 percent effective, and researchers believe it could be used to vastly improve animal welfare in laboratory tests and agriculture.

Often in farming or laboratory studies on animals, only one sex is required. For example, in dairy farming only females are required. In research into reproduction, only males or females would be required, depending on what was being investigated.

Normally, the animal of the wrong sex would be killed at birth, posing a major animal welfare issue, especially in agriculture where males are seen as surplus.

It is estimated that up to 6 billion male chicks are killed every year because they do not lay eggs and do not make good meat. In the U.S., this amounts to around 300 million male chicks annually. In the dairy industry, hundreds of thousands of male calves are killed, often in the first week of their lives.

In their latest research, published in Nature Communications, Charlotte Douglas from the U.K.'s Francis Crick Institute looked at gene editing to solve this problem. With colleagues, Douglas set about developing a genetic system that inactivates embryos just after fertilization so that only one sex develops.

The system involves CRISPR gene editing. The team spliced the DNA allowing them to alter the mice genes, placing one element onto the male's X or Y chromosome. This would then be inherited by the female or male embryo. Another gene involved in DNA replication and repair was then targeted. This means that when the embryo reached an incredibly early stage—between 16 and 32 cells—it could not develop any further.

In doing this, researchers were able to control what sex litters were with 100 percent efficiency. They also found litter size was not reduced significantly, with numbers between 61 and 72 percent of the control litters.

The team believes that because the genes targeted are found across mammalian species, it could be used in other animals to improve welfare. "Animals are essential genetic tools in scientific research and global resources in agriculture," they wrote in the study. "In both arenas, a single sex is often required in surplus. The ethical and financial burden of producing and culling animals of the undesired sex is considerable...Our approach, harnessing the technological applications of CRISPR-Cas9, may be applicable to other vertebrate species, and provides strides towards ethical improvements for laboratory research and agriculture."

James Turner, one of the study authors, said in a statement: "This work could have immediate and valuable impact in scientific laboratories, as we've shown how it is safe and effective in mice, a common mammal used in medical and scientific research."

Peter Ellis, another author on the study, said that ethical and regulatory issues need to be addressed before it is introduced to the agriculture industry. "Further research is needed, first to develop the particular gene editing toolkits for different species, and then to check they are safe and effective," he said.

PETA, however, says the research overlooks the wider problem of animal cruelty within these industries. Dr. Julia Baines, PETA's Science Policy Manager, told Newsweek: "Animals are not ours to manipulate, and they can't consent to humans tampering with their genomes to increase corporate profits. Mice are intelligent, sensitive, social beings who have their own lives, feelings, and desires ... Just as genetically modifying humans is unacceptable, so is doing it to other animals who can't protect themselves from such invasive procedures.

"Gene tweaking doesn't help animals still being bred to feed the demand of the laboratory supply chain. The only way to stop cruelty to all animals in laboratories is to make the transition to modern, human-relevant science that doesn't involve the use of animals."

This article has been updated with quotes from Julia Baines.