Legislation governs the importation of bull semen into Jersey
The first calves bred using imported bull semen have been born in Jersey, ending a tradition of more than 200 years' standing.
In the 19th Century the importation of cattle was banned by the States to ensure a pure breed, but using American bull semen was approved in 2008.
Most farmers said this would give a higher milk yield and lower illness.
But one farmer, Trevor Barrette, said this was not an issue and there was more demand for pure-bred Jersey cows.
The Home Farm dairy herder said: "Personally it's all down to the feed, the management and how they're looking after their cows - I don't see a big problem."
Paul Houze, of Lodge Farm, has twenty calves bred using imported semen, which he said were developing normally and were healthy.
Stringent legislation and licences have been put in place by the States to govern the importation of the bull semen.
Mr Houze told BBC Jersey: "They're quite onerous and they're probably twice as stringent as any European protocol, so that we need to verify that there are at least seven generations of pedigree stock behind the bull from which the semen's used.
"And if there's a known ancestor of another breed, it's banned from entering the island."