The mistake was discovered by the American Jersey Cattle Association
More than 3,000 bulls have been DNA tested in the United States to check they are pure-breed Jerseys.
There used to be a complete ban on the importation of bull semen to Jersey, but restrictions were partly relaxed about two years ago.
Last week it was revealed imported semen from a non-pedigree bull had been used for breeding.
Despite the mistake, Jersey's assistant economic minister said the purity of the herd had not been compromised.
Semen brought into the island must come from a bull with at least seven "pedigree generations" behind it to maintain the Jersey herd.
But the American Jersey Cattle Association found non-pure frozen semen had been sent.
The association called the error "regrettable" and it has since arranged to have the DNA testing carried out.