At the courtyard birds, as with other categories of animals, genetic advancements are usually achieved through extensive breeding and selection programs. However, addressing specific issues and diseases through traditional selection is difficult or even impossible. With the introduction and growing experience in genetic editing techniques, things could accelerate, as reported in a study published by PoultryWorld.

Introducing Desired Changes

Gene editing allows animal breeding programs to introduce desired changes in a controlled manner and at a faster pace than is possible through conventional selection alone. As Dr. Alison van Eenennaam explains, gene editing involves guiding DNA-cutting enzymes (site-specific nucleases) to make a targeted, specific cut at a predetermined DNA sequence.

She is also the geneticist from the University of California, Davis, who used gene editing a few years ago to create a bull calf that could produce deformed sperm.

Regarding how gene editing can work in animal breeding, Van Eenennaam says:

"Depending on how the cut is repaired, you can either have inactivation of the gene at the target site or a modification of the functionality of that gene. Alternatively, DNA could also be introduced at the cutting site using a DNA repair template that contains a sequence originating from that organism, another species of it, or a different species."

However, genetic engineering is a 20-year-old technique that is not straightforward. Foreign genetic material is introduced into the genome using a DNA repair template in the absence of site-specific DNA-cutting nucleases. "GalSafe" pigs (created in 2002) and "AquAdvantage" salmon (created in 1989) became the first genetically modified (transgenic) farm animals approved for human consumption in the US in 2020.

Legal Usage

Gene editing regulations are a complex issue, and many geneticists, including Van Eenennaam, consider the regulatory frameworks in multiple jurisdictions to be restrictive and illogical. Gene editing in the EU, for example, is regulated similarly to genetic engineering.

Even more oddly, in the US, genetic editing of animals is currently regulated by the US Food and Drug Administration, which classifies any intentional genome modification in an animal's genome as a new animal drug and, therefore, applies the regulatory frameworks used for drugs.

Governments in other jurisdictions, such as Brazil, Australia, and Argentina, see gene editing as similar to conventional breeding, at least in situations where a gene is deleted, and no new or foreign DNA is introduced.

Disease Control Potential

For courtyard birds and other types of animals, traits involving a single gene (such as feather color) are highly suitable for gene editing, while traits involving many genes (such as feed conversion rate or growth rate) are not.

Complete disease prevention is a very intriguing area for gene editing applications because, in many potential scenarios, eliminating a single gene can prevent the mastery of a disease process in the first place. For example, you could eliminate the production of a cell surface receptor used by a virus or bacteria to attach and enter a cell.

Indeed, new interventions can be made for both existing and newly emerging pathogens by gene editing in new in vitro cell culture systems, according to a group of researchers at the Roslin Institute in Scotland in a recent review titled "Genome Editing of Chickens for Investigation of Poultry Pathogens."

Progress So Far

In another paper on gene editing in courtyard birds, other scientists from the Roslin Institute and the University of Edinburgh highlight an achievement dating back to 2017 when researchers made genetic modifications to the somatic cell lines of chicks, leading to resistance to avian leukosis virus. The gene modification targeted the cell receptor used by a specific strain of the virus.

These scientists also point to other researchers who, in 2016 and 2019, deleted a small region of chicken DNA that plays a "key role in the replication of avian flu virus in both chickens and waterfowl."

They summarize that, while "many gene editing approaches focus on targeting host genes involved in mediating virus entry, with a particular emphasis on receptors, as demonstrated by the example for avian flu, host genes also play an important role in other stages of pathogen replication. cycle and also provide editing targets for resistance or resistance to diseases."

Welfare and Sustainability

There is also hope that the thorny issue of culling male chicks from egg-laying poultry breeders can be addressed through genetic editing. The governments of Germany and France have already banned this practice, requiring egg industries there to use technologies that detect the sex of embryos before egg hatching.

Most other EU countries are considering similar bans. However, geneticists in Israel are using gene editing to create hens that lay eggs from which only female birds hatch.

A group from the Israeli Agricultural Research Organization's Volcani Center achieved the creation of hens that produce only female chicks after 7 years of research with an American-Israeli company called Huminn.

When eggs laid by genetically modified hens are exposed to blue light for several hours, male embryos do not develop. Female embryos are not affected by the blue light, develop normally, and hatch when fully developed.

Future Potential

Achieving disease immunity in courtyard birds has been, thus far, a very challenging task. Dr. Huaijun Zhou, a professor and chancellor at the University of California, Davis, notes that, at this point, geneticists are primarily using gene editing in courtyard birds to understand the functions of different genes in the bird genome.

Zhou is also the director of the Feed the Future Innovation Lab for Genomics to Improve Poultry and a recipient of the NAS Award in Food and Agriculture Sciences. But he sees a bright future ahead: "If gene editing can be used to control disease, that would be a very welcome achievement with great potential."

He concludes that despite the great work done so far, the scientific community has just scratched the surface of the potential benefits of gene editing.