"... action needs to be taken to prevent Lewis from further damaging the image of thoroughbred breeding by continuing to operate a commercial stud standing a NZTR [New Zealand Thoroughbred Racing] registered stallion and caring for NZTR registered broodmares."
The RIU investigated and issued a report on Mr Lewis' operation after it received multiple complaints including from clients, workers and vets who had dealt with him.
The first complaint came in October 2016 which prompted a visit from RIU staff.
"There appeared to be 6-8 horses including one foal with the mares 'ribby' and in light condition but not at a level that required SPCA intervention," the report says.
But RIU continued to receive complaints.
In May, four people - some of who had assisted Mr Lewis with the stud farm - contacted the RIU alleging they "had serious concerns for the welfare of horses on Lewis' properties and his ability to care for them".
Mr Irving's report said their statements included allegations which detailed "long term systematic neglect and mistreatment of horses in Lewis' care and his incompetence and inexperience operating a thoroughbred stud".
In 2015 North Taranaki SPCA removed five broodmares from Mr Lewis' care for welfare reasons.
Around that time Mr Lewis set up Regal Fern Lodge in Waitotara before moving it to Kaitoke to stand stallion Little Wonder which he leases.
Mr Irving suggested to the owner of Little Wonder "that due to Lewis' inability to competently run the stud and the ongoing welfare issues concerning the broodmares that she find an alternative home for Little Wonder, or I would be recommending to New Zealand Thoroughbred Racing that the stallion is deregistered".
Instead the owner believed complainants were "out to get him".
In speaking to RIU, Mr Lewis blamed others for the state of his horses.
"I informed Lewis that I believed that as the person in charge of the stud he is solely responsible for the welfare of his horses and due to his neglect he was bringing thoroughbred racing into disrepute," Mr Irving wrote.
His report recommends preventing Mr Lewis from registering or filing any mare or foal returns with the NZTR Stud Book.
The Wanganui SPCA also visited Mr Lewis' property in June.
"They inspected 28 horses and gave them an average body conditioning score of 2/5. They returned to one of the properties two days later as they received information that Lewis had hidden the four worst conditioned mares," the RIU report said.
Earlier this week the SPCA said it was not able to comment any further.
