Michael Stiassny is missing a few cows - more than 1000. Stiassny was appointed receiver of the Crafarms group in October after the family-owned company collapsed under heavy debts and multiple prosecutions for effluent discharge.

Until its fall, the Crafar family had run the largest privately owned dairy company in New Zealand, with 20,000 cows spread across 22 properties.

But now some of those cattle have been taken - in possibly the biggest rustling operation this country has seen. Well, the "biggest one that anyone's ever had proof of", Stiassny said.

He said he was flabbergasted at the moonlight cattle migration which began on Friday afternoon and continued until yesterday.

"We're in the receivership business, and yes we see things that most other people don't, but we are - regardless of our experience - continually surprised."

Stiassny said the movement of stock contravened a court order and said he would be approaching police.

He said he had a suspect in mind for the heifer heist.

Allan Crafar did not return calls yesterday, but his brother Frank - also a director in Crafarms - said he and his brother had been at home in Reporoa since Thursday.

"We know nothing about it," he said of the missing stock.

There was bewilderment in the farming industry at the size of the mysterious cattle migration.

Federated Farmers head Don Nicholson said: "You don't just magic away that many cows."

He said the value of the haul of dairy beasts would probably exceed $1 million.

Federated Farmers dairy spokesman Lachlan McKenzie said: "It's extraordinary to my farming ears."

He said the cattle-movers would have trouble hiding their stash: "I could put 100 cows in a back paddock and no one would know, but 1000?"

There is dispute over the ownership of the cows, as the farm from which most of them vanished - Taharua Farm near Taupo - is run by sharemilkers, who own the stock.

McKenzie said the incident would be difficult to unravel. "It's a civil matter and possession is nine-tenths of the law."

Cattle were no longer branded, McKenzie said, "but there's usually a tag on their ear, but that can be removed and replaced pretty easily".

Taupo police were unaware of the missing cows when contacted yesterday.

Stiassny said the Crafars' debts exceeded $220m. They were all still living in their Crafarms-owned homes and, until last week, were still getting salaries.

"There are some poor people do who make mistakes in their business," he said. "They lose the business, they don't get paid by the the company after they lose their business, and they do lose their homes."