A farm in Cheshire has produced the first calves to be born in the United Kingdom whose sex was determined before they were conceived.

The Holstein calves - Charity, Clover and Cloe - were born in late May, using a technique pioneered in the US. It involves sorting the bull's semen into two groups, carrying either X or Y chromosomes, but not both.

X chromosomes produce female offspring, Y chromosomes males.

The births were the work of a British breeding company, Cogent, and a US firm, XY, Inc, the only company licensed to carry out sperm sorting in non-human mammals using US Department of Agriculture methods.

Changes to the industry

Cogent said the development "signals the success of a new breeding method, expected to completely change the dairy industry and dramatically reduce the number of unwanted male dairy calves".

Because female calves are smaller at birth than males, first calvings should be easier for the mother.

And there should be a significant drop in the numbers of male calves, which are killed as useless when they are a few days old.

Benefits promised for calf and mother

A subsidy worth �28m a year, payable to farmers for slaughtered male animals, is due to be phased out at the end of July.

The Farm Animal Welfare Council recommended in 1997 that "the sexing of semen should be used to reduce the number of unwanted male dairy calves".

Cogent and XY expect their new method, which is used with artificial insemination, to reach the market in the next two to three years.

They say their sperm-sorting technique has a 90% accuracy rate in producing the high concentrations needed to make selected cattle pregnant.

They say they will be able to replace the present "very inefficient system" under which 60% of a herd has to be made pregnant to ensure that 30% of the calves will be females.

The technique will be applicable in time to other species.

News of the discovery was carried by BBC Radio Four's "Farming Today" programme.