by Jennifer Allerton, British Science Festival

What does it mean to have food produce that is genetically edited or genetically modified? And what reason is there for changing the genes of the animals we eat? These are the questions Dr Christine Tait-Burkard set out to answer in her talk at the British Science Festival.

Selecting traits we want to see in our livestock is certainly nothing new. For 10,000 years, humans have been domesticating animals and breeding the least aggressive with each other. In the 18th century, at the height of the agricultural revolution, Robert Bakewell wrote about intentionally and systematically breeding livestock to heighten certain characteristics, a process known as selective breeding.

Selective breeding is not without its drawbacks and raises ethical questions about whether the changes in the qualities of livestock which benefit the agricultural industry are in fact harmful to the welfare of the animals. But the use and impact of selective breeding varies widely. For instance, as Dr Tait-Burkard pointed out, organic livestock farming is only possible because of the selective breeding of more robust and healthy animals, with less need for drugs.

When it comes to genetic engineering, there are further distinctions. Genetic engineering describes any methods of direct manipulation of an organism’s genome using biotechnology. This includes transgenesis, where a gene from one organism is inserted into the genome of a different organism. Examples of this include goats who have received a copy of the gene coding for the human protein insulin. Insulin can then be extracted from their milk for use in medicine to treat diabetes. Under the umbrella of genetic engineering is genome editing, which involves either removing or “turning off” certain strands of DNA without adding any new genetic material.

Genome editing is the technique that Christine and colleagues at the Roslin Institute, University of Edinburgh, have been using to try to tackle the problem of Porcine Reproductive and Respiratory Syndrome (PRRS). PRRS causes respiratory distress, fever, lack of appetite, and vulnerability bacterial infection. This last symptom unfortunately leads to an increased use of antibiotics. It’s estimated that around 50% of antibiotic use in pigs is due to PRRS-related bacterial infections. Suckling piglets who contract PRRS suffer severely and are unlikely to survive, and the need for widespread antibiotic use is a contributing factor in the rise of so called ‘superbugs’ – antibiotic resistant infections. PRRS is a costly, not to mention distressing, disease.

We've selectively bred animals for generations; it's argued that genome editing of livestock is the next logical step

Historically, the options available in the face of PRRS have been limited. Vaccines struggle to keep up with the rapid evolution of the virus into new strains, which leaves farmers faced with the difficult decision of “depopulation”, as it is euphemistically referred to.

The PRRS virus interacts specifically with a cell protein on the surface of pig cells that is important in regulating the immune response. The strand of DNA that contains the blueprints for synthesising this protein within the cell is made up of multiple sections of “protein-coding” DNA, separated by stretches of DNA which do not form part of the protein. The team at the Roslin Institute found that if, rather than removing this gene altogether, just one of these protein-coding sections in particular was removed, the cell was still able to create a copy of the protein that retained its normal function, whilst the site that the virus would bind to was no longer present.

This gene-cutting process is performed in sow’s egg cells, and the resulting piglets were found to be resistant to the PRRS-virus. In this case, “resistant” means that not only do the animals show no symptoms of the virus, but they do not infect other pigs they come into contact with.

The researchers also wanted to know if breeding the PRRS-resistant pigs would successfully result in resistant offspring. If your GCSE biology is rusty, then a quick reminder - you will receive one copy of every chromosome from each of your parents, resulting in two of every chromosome, which may be different from each other in terms of the actual DNA they contain. So, in the case of our piglets, they receive a copy of the gene that holds the blueprints for this protein from each parent, and may end up with two edited genes, no edited genes, or one edited and one unedited. In all pigs born with only one or no edited genes, the virus was still able to replicate, but pigs born with two copies of the edited gene were resistant to the PRRS virus.

This research has profound implications for the future of pig-farming and is big news for the field of gene-editing. The predicted increased animal welfare and decreased need for use of antibiotics are a huge result, and the nature of the process means that nothing is added, and the only thing in your bacon sandwich at the end of it all is 100% pig.