Nowadays, it is not very often that you see cattle with horns when you drive past or walk
through country fields. This is due to the common practice of de-horning, a painful
procedure in which the onset of horns in young calves are burnt away. One reason for this is
that horns can cause injury both to the cow itself and to other cattle. Also, these horns can
become broken, causing blood-loss and potentially life-threatening infection, which could
have devastating consequences for the cattle industry. However, the main reason for de-
horning is purely economic, as horned livestock take up more space and cost more to
In order to combat the ethical issues around the de-horning procedure, scientists have
developed a new technology in which a cow’s genome (genetic make-up) is edited so their
offspring are born hornless, removing the need for the painful procedure.
This technology is called TALENs, which stands for ‘transcription activator like effector
nucleases.’ Each TALEN molecule is made up of 34 identical amino acids (the ‘building
blocks’ of protein). The 12 th and 13 th amino acids are known as the ‘hypervariable region’,
meaning that the TALEN used for this technique is complementary to the gene that codes
for cattle horns. At the end of the amino acid chain is an enzyme called a restriction
endonuclease. This enzyme ‘cuts’ the fragment of DNA containing the mutation which
causes a cow to be born hornless (called the ‘POLLED’ gene). Two of these TALENs are
required to ‘cut’ the DNA fragment. Once the fragment has been ‘cut’, the DNA fragment is
inserted into a bacterial plasmid: a circular piece of DNA found in bacteria. The plasmids are then inserted into the bacterial cell using heat-shock.
The bacteria with the genetically transformed plasmids are then inserted into an adult cow,
mixed in with a saline solution to prevent the bacteria from bursting. This all means that the
parent cow will pass on the hornless gene to their offspring, because the mutated gene that
codes for ‘hornlessness’ is dominant.
However, there are many controversies surrounding this technique of genome editing. The
first is a common issue facing genetic engineering: the fact that some people believe we
shouldn’t be ‘playing God’, despite the obvious benefits of producing hornless cattle.
The second main issue is that the plasmids used to transport the mutated gene (also known
as vectors) usually contain two antibiotic resistant genes: one for trypsin and the other for
ampicillin. Every cell of the cow’s offspring will contain these antibiotic resistance genes
(due to cell division), meaning antibiotics will be ineffective in treating the cow. This could
potentially leave gene-edited cattle at higher risk from pathogenic bacterial infections. This
factor also somewhat invalidates claims of animal welfare benefits. It’s also one of the
reasons why the Food and Drug Administration (FDA) have not yet approved gene-edited
cattle for human consumption - the effects of consumption on humans is simply not yet
known. Also, the gene-edited cattle are considered as genetically modified organisms
(GMOs), which have always had a lengthy approval process for health and safety reasons.
The final factor that concerns many farmers are the reasons why cattle need their horns.
Horns are required for thermo-regulation, cooling, and are a defence mechanism against
potential predators, such as wolves and dogs.
In conclusion, it looks like genome-editing to produce hornless cattle will become
mainstream in the future due to its decreasing costs, efficiency, accuracy and pain-free
procedure. This technique has its controversies, but the disadvantages are often
outweighed by the advantages. However, the future of this technique remains unknown
within the cattle industry due to the ever-prominent discussion around the ethics of genetic
A.Spengler-Neff,2017,’Why do cows have horns?’, https://earthhaven.ca/why-cows-need-
Agence France-Presse,2019, ‘Gene-edited hornless cattle meat does not get FDA approval
for human consumption’, https://www.firstpost.com/tech/science/gene-edited-hornless-
C7jbdsSt1i, 2019, ‘Genome-edited bull passes hornless gene to calves’,
Rigor Morty, 2014, ‘TALEN: a specific DNA editing tool’,
https://www.youtube.com/watch?v=BwEiNySbBLY, date visited: Monday 14 th October 2019