The maximum penalty for each offence is 12 months' prison or a fine of $50,000.
The SPCA prosecution relates to the botched castration of two 14-month-old Friesian bulls carried out by Thomson after he sold them to Green late last year.
The SPCA summary of facts stated Green, who was not an experienced farmer, bought the bulls to help keep the grass down in paddocks on his lifestyle property.
Green and Thomson agreed the animals should be castrated before being handed over.
About September 4, the defendants met at Thomson's Paengaroa property where he tried to castrate the bulls using the standard process of tightly fitting an approved rubber ring or band to the animals' testes.
When he was unable to do so, Thomson loaded the bulls onto a trailer and drove to a nearby Paengaroa service station carpark with Green following.
After buying cable ties and some thick rubber bands from the service station, Thomson again tried to castrate the bulls by placing the rubber bands around their testes.
Thomson did not use any anaesthetic.
He told Green the bulls' testes would fall off in about eight weeks, and if this did not happen he would do the procedure again.
Green then drove the trailer with the bulls to his property in Whakamarama.
On October 16, the SPCA received a call of concern about two bulls on Green's property that appeared unwell, and an SPCA inspector and a veterinarian visited.
SPCA said it was immediately apparent the bulls were infected in their testes area and a putrid odour could be smelt from some distance away.
Their testes developed severe infections, including gangrene and sepsis, which would have caused the bulls undue pain and distress, and were surgically removed,
Green told the SPCA inspector he didn't believe anything was wrong with the animals and they seemed content and happy.
He told the inspector he was waiting for eight weeks after the castration attempt to see if the testes would fall off, as Thomson advised him to do.
The vet provided clear post-operative care advice and told Green to call the clinic if any concerns arose. One of the bulls subsequently developed sepsis and was euthanised.
Following the September 29 court appearance, Judge David Cameron has released his written reserve decision to the Bay of Plenty Times.
The judge said Thomson failed to seek advice from a veterinarian on how to carry out the procedure, had no previous experience of castrating cattle, nor received training in the correct use of the method.
"Despite the lack of experience, Mr Thomson took it upon himself to attempt to castrate the bulls using a totally ineffective method.
"As such, the bulls' testes and scrotum swelled to two to three times their normal size. This caused inadequate tissue perfusion, necrosis, gangrene and sepsis. These then caused secondary bacterial infection and undue pain and distress."
Cameron also said the fact Thomson claimed he sought advice from a neighbouring farmer was not an excuse for his failure.
The judge said in relation to Green's offending, veterinary advice showed both animals were infected in their testes area.
"The veterinarian concluded that the animals' veterinary needs had been disregarded, and there was ample opportunity to remedy the situation," Judge Cameron said.
"Both Mr Thomson and Mr Green have to be held accountable for their actions, and I denounce their conduct and seek to deter them and like-minded individuals from failing to care for animals properly."
Judge Cameron said he found both men were equally culpable, but in different ways, and fined each defendant $3900, after taking into account their previous good characters, lack of prior convictions and guilty pleas.
The judge ordered the fines to be paid to the SPCA, along with $600 costs towards SPCA's legal costs, and $1809.90 in reparation for veterinary expenses.
Thomson and Green must pay a half-share each of the legal costs and reparation.
In a written statement, SPCA chief executive Andrea Midgen said the improper way in which this procedure was carried out was "inhumane and totally avoidable".
"It never ceases to amaze me how some people don't seem to understand that animals feel pain just like we do, and in this case, the bulls would have felt severe pain
for many days after.
"With no anaesthetic, these animals would have suffered immediate pain throughout the procedure and as incorrect tools were used, including rubber bands and cable ties, the animals would have felt that pain for days afterwards."
