The sex of six calves born last summer - three male and three female - was determined before fertilisation using the technique, which scientists predict will be widely used within a few years.
Small differences between sperm carrying the male 'Y' chromosome and those bearing the female 'X' chromosome enabled a sophisticated sorting device to separate the two types of sperm cell at the rate of about 2 million an hour. With the help of techniques routinely used for in vitro fertilisation of animal embryos, scientists fertilised bovine eggs with 'Y' sperm to produce male calves and with 'X' sperm to make female calves.
Cattle farmers could find the technique helpful in skewing the natural 50:50 ratio of males to females in their favour - dairy farmers want a ratio of one female replacement calf for their herd to three bull calves to sell for beef and beef farmers prefer bull calves only.
In this week's edition of Veterinary Record, scientists from a Cambridge biotechnology company, Mastercalf; the Institute of Animal Physiology and Genetics Research, also in Cambridge; and the US Department of Agriculture in Maryland, publish details of the research that led to the birth of the six Holstein Friesian calves. Professor Chris Polge, scientific director of Mastercalf, said pre-determining the sex of embryos had occurred on a limited scale on other animals, such as rabbits, but this was the first time it had been done in cattle. However, the procedure is complicated and large- scale trials are necessary before the idea could be adapted for commercial use. 'This may take two years,' he said.
David Cran, the leader of the scientific team at Mastercalf, said that farmers would be able to choose the sex of their calves with an accuracy of greater than 90 per cent. He said that having the power to alter the sex ratio of new-born calves - attempts were first made 75 years ago - 'will cut calf wastage and the economic and qualitative improvements will work through to the benefit of the consumers'.
Mastercalf already sells unsexed beef embryos and the company believes that sexed embryos will increase the value of resulting calves. The company is now producing more than 100 grade- one sexed embryos for field trials plannned for farms in Scotland, Cheshire and Shropshire.
Professor Polge said there were no ethical problems with the new technique and denied that it was tinkering with life: 'I don't think we are tinkering with it so much as putting it together, to be used more effectively for what the farmer wants.' He stressed that the procedure did not involve genetic engineering but only in vitro fertilisation, which had been used for many years and had full ethical approval.