Horses are regularly being castrated without anaesthetic by unqualified people on the East Coast and in Hawke's Bay, say authorities.
The practice appears to have been going on for years, driven by a lack of vets in remote areas and vets' charges of about $250 a horse, says the Ministry for Primary Industries (MPI).
"It appears to be a practice that is well ingrained in the culture of the farming and rural community of the wider East Coast area," said MPI's Mike Green.
Following investigations it appeared the practice was more widespread than at first thought, and the unqualified people were castrating their own horses and also offering the service as part of their businesses.
Many large station owners were using unqualified castrators despite them knowing it to be illegal, he said.
Most appeared to have not concerned themselves with the fact it is illegal.
He was not aware of any botched operations, but MPI had written to three people who had been carrying out the operations and six people who had used their services.
Unqualified castrators can be fined up to $50,000 or be jailed for 12 months.
None of the people spoken to were using anaesthetic, he said.
"I would imagine they would want anaesthetic used if they were undergoing that procedure," Mr Green said.
By law castrations are a surgical procedure that must be carried out by either a vet or a trainee vet under supervision. If things went wrong an unqualified person would find themselves out of their depth, he said.