It's not only human dads that will celebrate this Father's Day

It's not just human dads that will be celebrating this Father's Day. In fact, one four-legged creature has fathered thousands of daughters and, with 1200 more on the way, this year he's also helping to contribute millions to the New Zealand economy.

Meet Sierra the super dad - he's the country's top breeding KiwiCross bull.

The seven-year-old has already fathered a staggering 1700 daughters and over the next three years that number will rise by more than 80,000.

Simon Worth provides farmers with the best bulls for dairy production. It's a $300 million business.

He says bulls like Sierra father three out of every four cows in New Zealand.

"His BW, or genetic worth, is a direct reflection of how his daughters are performing right around the country. He's very good. He's at the top of the charts."

If you've driven past a dairy herd anywhere the country, chances are they've been artificially inseminated...

"Through our liquid semen, likely to have about 160-odd thousand straws go out - so those straws are actual inseminations into the national dairy herd," says Mr Worth.

Spring is the peak dairy cow-mating season, and farmer Brad Payne has decided to use Sierra's super genes. The bull can produce thousands of calves in one go.

"So we have a stainless steel pistolette... cut the tip off, sheath over the top and then you artificially inseminate the cow," says farmer Brad Payne.

Mr Payne has about 50 of the calves fathered by Sierra on the way.

"He's a fantastic Dad," says Mr Worth. "He better because he's got 100,000-odd coming."

Hopefully Sierra gets to have a rest on Father's Day.