Animal Defenders International


Animal Defenders International

Inside a GM animal factory

Posted: 12 July 2012. Updated: 4 December 2012


Genetic modification (GM) has been the biggest growth area in animal experimentation for two decades. More than half of the experiments in the UK are now on genetically modified and harmful mutant animals – 1.6 million. These are the animals the animal research community want to scrub from the records.

An undercover investigation by the NAVS takes you inside the Medical Research Council (MRC) Mammalian Genetics Unit in Harwell, Oxfordshire. This is the reality of a GM factory churning out animals that are discarded by the sackload.

GM animals have been heralded as a new research tool.

The animals are given a deliberate genetic defect; prolonged suffering arises from repeated surgeries, egg collection, implantation, repeated blood and tissue testing.

They live in tiny spaces, in sterile, barren environments with no stimulation.

The GM process itself can cause longer pregnancies, higher birth weights, increased deaths at birth.

Finally, there is the effect of the genetic defect itself – severe health problems, mutations, premature death.


Only 3-5% of the babies actually have the desired genetic defect, so huge numbers are killed and discarded.

Body count at MRC Harwell: The death toll of Britain’s GM industry runs into millions.

The main animal facility at the Mammalian Genetics Unit at Harwell can house 65,000 mice (1). The problems of over breeding and an inability to manage colonies, coupled with staff inadequacies, meant keeping control of the colonies was almost impossible.

The NAVS investigator noted confusion in the breeding of mice and signs of copulation in females being missed, resulting in unplanned litters (2).

On one occasion a young male mouse had been mated by his father and when he removed the “copulatory plug” from his anus, half the hair around his bottom also came away. Parents also attacked and ate their pups.

The NAVS investigator attempted to prevent the deaths of some small mouse pups by leaving them with their mothers a little longer, but was reprimanded and told to accept that ‘some will die’ (2).


The aim of most GM projects is to create animals with a particular trait, in order to “model” human conditions – animals are intended to be abnormal in some way. Deformities and abnormalities included: severe limb deformities; fused lung lobes; Huntington’s disease (HD) mice with hard lumps in their abdomens, strong tremors, immobility, priapism (painful swelling of the penis) and weight loss of up to 30%; cataracts and other eye problems; mutants with extremely short faces and upturned noses caused by abnormal bone growth; self harm, such as animals chewing through their own skin and congestive heart failure which caused one mouse to swell to about three times normal size (2).

On one occasion, female mice aged 3.5+ weeks were put to mate with males about three times their size. The older males tried to mate with the females who became distressed and vocalised (2). On another occasion, an animal had to be killed following fighting.

As with many of our previous undercover investigations, there were examples of cage “run outs” (where water leaks into the cage). This leaves the animals in wet cages, which can result in severe cold, discomfort and even death. One mouse had suffered a run out and its feet and face had become bright pink. It appeared to have hypothermia and so was killed (2).

References: 1. Contemporaneous notes 07/08. 2. Contemporaneous notes 06.

© Animal Defenders International 2019