Advancing GM: Genome Editing To Make Hornless Cattle - By Maria Munden

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

transport.

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

modification.

References:

A.Spengler-Neff,2017,’Why do cows have horns?’, https://earthhaven.ca/why-cows-need-

horns-c553.php

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-

cattle-meat-does-not-get-fda-approval-for-human-consumption-7466371.html,

C7jbdsSt1i, 2019, ‘Genome-edited bull passes hornless gene to calves’,

https://newsfortomorrow.com/index.php/2019/10/07/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