Two vets examined the dog and, suspecting deliberate castration, anaesthetised the animal and examined further. This confirmed their suspicions and they notified the SPCA.
The vet who removed the dog's scrotum commented that the dog would have suffered significant pain and distress during and after the botched home surgery.
When interviewed, the man admitted castrating his dog and described the procedure he had used.
"The defendant admitted he is not a qualified veterinarian, did not seek any advice prior to carrying out the procedure, and claimed he was unaware that home castration was illegal in New Zealand," the SPCA said.
He has been convicted in the Hamilton District Court on a charge of performing a significant surgical procedure on an animal despite not being a vet. His sentence is to do 150 hours of community work and pay a fine of $350. He must also pay $500 towards legal costs and reparations of $442.40. He was also disqualified from owning animals for five years.
"This dog owner has put his animal through horrific pain and suffering and it could all have been avoided with a single trip to his local vet," said SPCA chief executive Ric Odom.
The man surrendered the dog to the SPCA. It has since made a full recovery and has been adopted by new owners.
"The SPCA believes that de-sexing is one of the most important things we can do for animal welfare and to help your pet have a longer, healthier life," said Mr Odom. "But we warn the public not to take matters into their own hands."