Scientists in Japan say they have succeeded in cloning a cow -- making a genetic copy of an adult animal.

The researchers at the Ishikawa Prefecture Livestock Research Centre said two cloned calves were born on Sunday, exactly two years after the birth in Scotland of Dolly the sheep, the first animal ever cloned from an adult.

Experts said it proved that Dolly was not just a one-off; they said by cloning adult cows with particular qualities, scientists could begin developing herds to produce more milk or better beef.

The Japanese scientists said they placed cells from an adult animal into unfertilised eggs whose nuclei had been removed.

They then fused them to produce embryos that were later implanted into the wombs of cows.