I've been thinking about it and I have lived and been part of the greatest change in farming within history. When I got married in 1940 and got a start on the home farm I milked 33 cows and had 120 sheep but you did everything by hand, whereas everything is done by machinery now.
"At one stage there were 73 dairy factories in Southland, one about every four miles because they had to be within a reasonable distance for a horse to deliver the milk. Now we've got one (Fonterra's Edendale Dairy Factory) – the biggest in the world," he says.
Today his family trust owns two 121ha dairy farms, each carrying 350 cows on the same family land at Seaward Downs, and both run by 50-50 sharemilkers.
"All my life I always tried to give the impression I was a good employer because it meant you got a better choice (of staff)," he says.
"The people I've got have been with me for 12 years now. They are wonderful, very honest people. I couldn't manage without them now. We meet them once a month and they just do it. All I've got to do is pay for it."
He winces at the memory of losing his driver's licence and his independence earlier this year, but his sharemilkers collect him for his monthly farm visits "so I'm right up with the play", he says.
A couple of years ago the family trust invested in two large wintering barns, one on each farm housing all 700 cows through the winter.
He says the transition to feeding cows indoors was a steep learning curve for him but "it is the best thing I ever did".
"We used to winter cows on a 500-acre property at Fortrose, but it was very difficult to put condition on them on winter crop. When we put the wintering barns up, the cows came out of winter in as good a condition as they were all season.
"When you feed silage in the paddock you lose 30 per cent of it," he says. "Feeding under cover on a concrete floor in barns you use all of it.
"On winter crop you give them as much as they can eat. But in a barn they only eat 60 per cent of what they would to maintain condition out in the open. Their stomach shrinks and they haven't got the same capacity, so you bulk it up with straw."
Outside the farm gate, McKenzie is perhaps better known to Southlanders for his lifetime of community service, for which he was awarded the OBE in 1986. He was also a Justice of the Peace for 56 years.
He is a founder and life member of the Edendale Veterinary Club, a farmer-owned organisation that has veterinary clinics in Edendale and Kennington operating under the trading name of Vetco. He only retired from the board in 2013 after 53 years of service when his hearing deteriorated.
He was elected onto the Southland County Council in 1949 and the Southland Catchment Board in 1964. He was only on the catchment board for six months before he was elected chairman and soon after became president of the New Zealand Catchment Authorities Association.
"It was the first national meeting I'd ever been to and I started asking questions about lobbying MPs for funding," he says. "They assumed I knew what I was doing and named me as president."
He told them he was only prepared to take on the job if the association established an office in Wellington, so he had a base from which he could lobby Government ministers.
"So I did it," he says. "It stretched me a bit but we did it."
As a councillor serving on both the Southland County Council and the Southland Catchment Board, he "accidently" found himself involved in everything going on and never stopped asking difficult questions of engineers or politicians.
"I had to teach myself to skim read to cope with the reams of paper work," he says.
"I've had no education to speak of so when engineers were explaining something to me I asked them to explain it in simple terms. Strangely enough, they quite enjoyed that, being invited to explain themselves in terms a layman could understand."
He built strong working relationships with influential politicians of the day and found a good way to gauge their value.
"What I found with politicians was that with those who you could talk to it was easy, but those people who talked at you were a waste of time.
"The most satisfying thing I achieved was getting a 75 per cent government subsidy for catchment works in Southland," he says. "All the works we did couldn't have been achieved without government money.
"I went into farming politics to try and help people. By and large I've been fairly successful," he says. "When I make a decision, whether it's right or it's wrong, I'll stick with it."
Although now retired from all community work, he is still politically and socially aware and likes to keep his mind active.
In 2008 he challenged Environment Southland's application for a resource consent to discharge waste water from a sewerage scheme for Wyndham and Edendale into the Mataura River.
From his sunny room in the Wyndham and Districts Rest Home, he keeps hands-on control of his dairy farms and a close watch on local and world events through his desktop computer.
"You've got to keep your mind busy and I read an awful lot too," he says. "The trouble is I can read an ordinary book in three to five hours. If it's a really good one I'll read it two or three times."