A record number of twin Hereford calves have been born on a Kaipara farm near Dargaville.Owner Sam Biddles said his cows had produced 11 sets of twins already this calving season, with another quarter of the herd yet to give birth.Biddles is a month into calving at his 500-hectare farm, which has been in his family for three generations, and he has never seen so many multiple births.About 380 Hereford cows are calving this season, and while Biddles usually gets a handful of twins among them, this year he has had more than 10."We average between five and seven sets of twins usually and this adds an extra dimension of work obviously. I'm not sure exactly how this has come about."Mild weather this year compared with last could have contributed to the large number of twins.SuppliedCalving started more slowly this year and sometimes there was no rhyme or reason for why these things happened, he said.'We generally take one of the twins off the cow and bucket-feed them as the cow would be eating too much pasture. Or we mother one of the twins onto another cow who has lost a calf."His Hereford cows were in excellent condition, he said, with a great temperament.They were also happy cows, which made him happy too.The farm raised the male calves into 15-month-old bulls for the dairy service market, with a sale held each year. Any female calves not retained for breeding were fattened and sent to the works, Biddles said.Mild weather this year compared with last year, when the weather was atrocious, could have contributed to the large number of twins on his stud farm, he said, but added it was a mystery.At the current birth rate, he may even end up with a dozen sets of twins, he said.