Gene editing could rid sheep of problematic long tails

Long tails have long been a problem for sheep producers around the world, but a research project led by Washington State University graduate student Brietta Latham may eliminate this trait, reports Devin Rokita, WSU College of Veterinary Medicine, in an article: "While some native breeds of sheep naturally short-tailed, most sheep are long-tailed, which can lead to hygiene and health problems, including a painful and potentially fatal condition caused by blowflies that lay their eggs on sheep. Animal tail docking is the industry standard, which is painful for the animals and labor intensive and costly for producers. 

Latham recently received a three-year USDA fellowship for her proposal to develop a gene editing strategy to shorten the tails of Suffolk sheep and eliminate the need for tail docking . Suffolk sheep are among the most widely bred sheep in the US.

“Our research will provide the industry with an alternative to tailings and improve animal welfare in our food production systems,” says Latham. “It will also increase the efficiency of sheep farming by eliminating the cost and labor associated with tailings removal.” 

Humans have been influencing genetics for centuries to select desirable traits in both plants and animals. Traditionally this has been achieved through selective breeding, which may take several generations to achieve the desired results. Latham, in his second year of doctoral studies under Professor John Oatley at WSU's School of Molecular Biosciences, plans to do it in a short time. 

“Genetic modification has been going on since we started raising animals at home - every time we decide to breed one animal with another animal to improve a certain production trait, we are making genetic selection. With gene editing, we're just speeding up the process. Using tools such as CRISPR-Cas9, it is possible to precisely edit specific regions of a cell's genome by removing, adding or changing genes,” she explains.

Earlier genetic studies have identified a gene thought to be responsible for tail length in sheep. Latham plans to knock out or remove this gene from long-tailed sheep embryos and replace it with a short-tailed breed. She used her strategy to successfully shorten the tails of mice.

“This is a modification that already exists in sheep. We're just taking this change that we're seeing in short-tailed sheep in China and Iran and we're bringing it into long-tailed sheep of European origin,” says Latham.

The edited embryos will be transferred to female sheep, who, after a five-month gestation period, should give birth to healthy lambs with short tails. These lambs must be able to pass on the desired trait to their offspring.

“The most important thing about gene editing is to make sure we get what we call germline transmission. We want the changes to show up in the gametes, eggs, and sperm that the edited animal produces. That's how we get the transmission from generation to generation,” says Latham. 

People often mistakenly confuse gene editing with the more controversial genetic modification through transgenesis. Gene editing does not combine the DNA of other species and does not attempt to create something that would never happen in nature. Instead, gene editing aims to bring about desired changes in animal species that could occur naturally but would take decades through selective breeding. "We rely on the changes that naturally occur in animals, gene editing is recognized as a safe practice that does not harm either the animals or the people who consume them," the expert concluded.