Aged only 22, Mr McRae found he kept waking with pain in his back and kidney area.
"I got really sick. I'd been working on a farm in Canterbury and found myself with this constant dull ache and throbbing pain."
A visit to the doctor led to a diagnosis of a "muscle spasm" - the first of what would become a long list of wrong calls by health professionals - and a prescription for anti-inflammatories.
Two pills a day kept the pain away, but as time went on Mr McRae soon found himself upping his dosage. The pain kept coming back.
He continued on "in agony" and his prolonged use of medication eventually led to a stomach ulcer.
A seemingly "endless" schedule of visits to doctors and health specialists was not solving the problem.
"None of them could tell me what was wrong. I don't know how much I was spending on prescription painkillers, but I was always in pain. I went to all sorts of doctors, specialists, and racked up the medical bills."
It all came to a head when Mr McRae collapsed in a heap on the floor, aged 30.
"I couldn't move. I thought I was paralysed and that I had had a stroke or something. They got me to hospital and it was back to the doctor's tests. They were completely bamboozled."
Contrasting diagnoses from specialist doctors left Mr McRae despondent about his future health and farming livelihood.
"One of them told me I faced a life of being confined to a wheelchair, never being able to play sport. He told me I would have to give up farming - at the age of 30. It left me hollow."
At his wits end, Mr McRae visited a naturopath - a crucial intervention which led to a lifestyle change and a converted outlook about farming.
"We sat down for two hours and he asked me a long list of multi-choice questions about my life - what I did, what I ate, where I worked, everything. At the end of it, he drew up a computer chart based on my symptoms of the . . . trace minerals I needed for full health.
"It was quite scary how stuffed up the mineral balance was."
He was given a strict diet to follow and during his consultation, he heard a new word for the first time - "organic".
"I was ready to try anything at the time. I couldn't walk properly. I was on crutches because of sciatica in my back and still had constant pain.
"Within one month of that diet . . . I was back playing touch rugby and pain free. It turned everything around unbelievably quickly," he says.
Mr McRae (now 35) insists he cannot prove it was exposure to "gorse chemicals and sprays" which he handled as part of his farming duties, but "I know it in my guts, that is what caused it all".
He now believes any chemicals used in the growing, manufacture, or processing of food will find their way into the human body as toxins.
After taking over Glendhu Station four years ago, one of the first moves he made was to go chemical-free.
Glendhu Station is less than a year a way from gaining complete organic accreditation - a process which usually takes four years.
• John McRae tells his story in our Focus on Farming publication, which is included with next Thursday's print edition of the Otago Daily Times.