Just over two years ago the first group of 10 cloned heifer calves were born at the Ruakura Research Centre, on the outskirts of Hamilton.
The genetically identical calves - cloned from an adult dairy cow - have now started having their own offspring after being artificially inseminated with the sperm
of one bull.
Only one cow failed to get pregnant and the new calves started arriving in August.
The mother cows are now being milked at a separate property at nearby Newstead. The milk is being used only for scientific research.
Dr David Wells said the work involved looking at the composition of the milk such as protein and lactose compared with the cloned mother's and also a herd of control animals.
It would be at least a year before any firm results were ready to be published.
It is an ongoing process as the cows will be mated again and have more calves next year to investigate the long-term effects of cloning.
The first animal to be cloned was Dolly the sheep at the Roslin Institute, in Edinburgh, in 1996.
Dr Wells and his team cloned two rams and two ewes from embryo cells later that same year.
But he said the 10 calves born in 1998 were among the first multiple births of cloned animals.
Although the calves have the same genetic make-up, they do not look the same, which "goes to show you can't control everything."
Since 1998, the chance of reconstructed embryos surviving and being good enough to transfer into recipient cows had increased from about 20 per cent to 40 per cent, Dr Wells said.
The chance of those embryos then surviving to full term had also increased, from 10 per cent to up to 40 per cent.
"To put that into perspective - in normal in-vitro fertilisation, only 50 per cent of the embryos transferred result in live calves."
- NZPA
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