Gene-edited dehorned cattle found to contain unexpected antibiotic resistance genes


Graphical representation of external DNA found inserted into the genome of gene-edited dehorned cattle in the US.

Gene-editing technique to produce precise and minor changes in the genome of organisms has been seen as the future for agriculture worldwide.

In 2016, a company named Recombinetics Inc. has gene-edited cattle to remove the genes controlling the development of horns. As a result of this genetic modification, dairy cattle were born hornless. The achievement was described in one of the most prestigious scientific journal Nature Biotechnology.

In their publication, Recombinetics researchers stated that the animals were free of off-target events after performing genome sequencing (

More recently, an independent analysis from the United States Food and Drug Administration researchers discovered that the same animals actually present unintended integration of full-length exogenous DNA used to edit the genome ( In addition, these exogenous sequences code for three antibiotic resistance proteins named ampicillin, neomycin and kanamycin. These are highly worldwide used antibiotics to treat respiratory tract and skin infections to severe bacterial infections and tuberculosis.

Although still under research stage, Recombinetics had previously petitioned FDA in 2016 to consider its hornless animals as generally recognized as safe – GRAS, a terminology that would imply no regulation as genetically modified organisms. But FDA decided otherwise to the petition as they understand that such genetic tinkering is “intended to affect the structure [or] function” of an animal. Thus, requiring animal regulation and risk analysis. Yet a final decision about gene-edited animal regulation by FDA is to be done in the US.

This independent analysis demonstrates how early we are in the timeline of understanding the impacts of editing the genomes of plants and animals as well as the emergence of a risk related to the lack of harmonized tools to detect unintended changes in gene-edited organisms. It serves as case study in how ‘early warnings’ may be incorporated into risk assessments at the cutting edge of technologyrequiring its regulation before these products enter the market.

More information on gene-editing technology assessment can be found at

Written by Sarah Agapito-Tenfen