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Mysterious inbred
cattle have survived long term
The research by Edinburgh University-based Peter Visscher, currently visiting Melbourne University's Centre for Genetic Epidemiology, and colleagues from the Roslin Institute and De Montford University in the UK, is published in this week's Nature. Inbreeding has been shown to reduce fitness in wild, zoo, laboratory and farmed animals, the authors write. On the one hand there is a loss of genetic variation, which may make the population less robust in response to changing environmental conditions. On the other hand, deleterious alleles (alleles are forms of the same gene) can accumulate. Whilst walking around in a museum with his two sons in Edinburgh one day, however, Peter Visscher came to hear of a feral herd of cows which have been allowed to roam freely in isolation for at least 300 years at Chillingham Estate in the north of England. "I wondered how they could be so inbred and yet still be a viable and fertile herd," Visscher told ABC Science Online. Visscher and team set out to study the herd of 49 Bos taurus cattle to see whether there was any variation in their genome. "We weren't allowed to take body samples from live cattle so we had to wait until various animals died and then take hair samples," he said. The researchers analysed the variation in genes at 23 sites on the genome. These sites normally show a lot of variation. Normally, any one cow would show variation at three quarters of these sites - they would have two different alleles at a particular site. In this herd, however, each cow had two copies of the same allele. Not only this but the same allele was found in all the other cows in the herd. Normally there are about 5 to 10 different alleles in a population of cows. These cows were remarkably genetically uniform and yet their population size had remained stable for over 300 years. Visscher and colleagues say their findings support the theory that while inbreeding is on average bad for a population, it can occasionally result in a population that is viable. "When combined with selection inbreeding may purge deleterious alleles," they write. Visscher says that this herd of cows is the most uniform population of wild animals ever to be described. In the same way that genetically uniform inbred laboratory mice make it possible to carry out more controlled experiments, Visscher hopes the Chillingham cattle may yield some useful knowledge to researchers. "They are valuable for controlled experiments such as those to determine the genetics of disease resistance," he says. "One experiment that researchers could do is to cross these cows with normal cows and find out if they are carrying genes that make them less susceptible to disease." Anna Salleh - ABC Science
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