The University of East Anglia has defended a research project which involved feeding mice their own faeces, after criticism from animal rights group PETA.

The organisation wrote to the university regarding the study, which it described as "highly concerning".

The research involves feeding slurry containing mice faecal matter to mice of different ages and observing how younger creatures function on a diet containing the poo of older ones and vice versa.

It is intended to investigate whether so-called 'faecal transplants' can reverse hallmarks of ageing in humans.

Such transplants would involve colonoscopies, to transfer gut microbes, rather than eating the material.

The mice study found that ageing gut microbiota can drive detrimental changes in the brain, stomach and eyes, and concluded that in the future faecal transplants could be used to restore cognitive function in elderly people.

But in its letter to the researchers, the People for Ethical Treatment of Animals (PETA) said: "There is an urgent need to modernise biomedical research away from the use of animals, with growing scientific consensus that far more is to be gained from enhanced support for human-relevant research methods and technology that are better suited to solving human biomedical and regulatory assessment paradigms than from reliance on animal studies.

"It is highly concerning that this study passed the university's animal welfare ethical review board given the prevalence of human clinical data available for this nature of work."

A spokesman for the UEA said: "We are committed to the ethical standards of animals in research and will only use animals when all other alternatives have been explored and exhausted to minimise their use as far as possible.

“UEA carries out animal research to further our understanding of diseases that have the most detrimental impact on human health and quality of life.

"This research concerned using gut microbe-based therapies with mice to combat decline in systems, including the gastrointestinal tract, peripheral circulation, nervous and immune systems, and the complexity of these systems cannot be replicated by using other techniques.

"We fully support the development, validation and adoption of appropriate alternatives to the use of animals, in order to minimise the use of animals in research."

The spokesman added that the university employs full-time animal care and welfare officer to make sure standards are maintained and the site is regularly visited by a veterinary surgeon.