"Using that system meant the trailers were then placed in a yard and the cows fed themselves from it," said Roy.
The group of farmers all came away from the trip with differing opinions as to whether it would work in Northern Ireland or not.
Back in the late 90s Roy was milking 200 cows and was realising how difficult and time consuming it was to walk a large number of cows from the farmyard to the grazing areas. It also was becoming apparent the amount of grass being lost with such a large number of cows walking over it in the fields.
Roy thought long and hard about the system and finally made the bold step of taking on zero grazing.
"I phoned Ed and told him I was interested," said Roy. "But I knew it would cost a lot of money for the machinery. In fact, the mower cost £11,000 new and the hay rack trailer was £6,000 new.
"Ed told me to try the system for a month and to pay it if I liked it. The month I tried it was particularly dry so I couldn't really test the system in typical Northern Ireland conditions. Ed told me to keep it for another month which was wet and it was them I took the decision to keep the machines."
Today Roy cuts enough grass for around 830 animals which includes the milking herd and followers. The only animals that graze outdoors are small batches of dry cows that are put out to a small paddock that is unsuitable for cutting.
Although the Harpurs are still using the very mower they bought 17 years ago, the trailer they used nowadays is a bit different to the original hay rack style machine.
Roy operated two of the older style trailers but was looking something a little bit bigger and one that would dispense the grass out onto a feeding passage.
With the herd r apidly expanding to 460 cows a new parlour was installed nine years ago and the cow accommodation was also revamped.
As part of that change, the cows then fed from a silage passage hence the requirement for a trailer to dispense the grass.
It just so happened quite by coincidence that Roy was over in Cheshire visiting Ed Walley again and learned about a larger trailer that was for sale at a nearby auction.
The trailer had been designed by Ed Walley and built by an outside engineering company. It was 25 foot long and was already a number of years old.
Roy knew a new trailer of this type would set him back £20,000 but was relieved to pay just over half that for the trailer at the auction.
"We were lucky to get the trailer for that price," said Roy. It is around 15 feet long and holds about seven tonnes of fresh grass.
"To feed over 800 head of cattle we harvest four loads of fresh grass per day and dispense the grass in the passages for the cattle.
"The cows are averaging 9,500 litres of milk per year with 2,800 of those litres coming from forage.
"When we bought that trailer it was only on a single axle. In order to make it more stable we added a second axle from an old slurry tanker we had in the yard.
"It has performed well all these years and the only mechanical work we have to do on it is add new bearings to the beaters which force out the grass driven by the pto.
"The floor on the trailer is hinged and the beaters simply push the grass out. It's a straightforward machine and has served us well all these years.
"The system works well for us as we have 135 acres to cut with around the farm. We also grow 85 acres of wheat to use in the diet feeder for the animals and cut 300 acres of grass for silage, three times per year.
"Back in 1999 people thought we were daft keeping the cows in and harvesting the grass for them to eat.
"However, here we are 17 years on and have never looked back. It is encouraging to see a number of other farmers using the same system and also the number of machinery manufacturers that offer a zero grazing type of machine, albeit built on forage wagons rather than the offset mower style."
As both the mower and the trailer are advancing in years, Roy has a second PZ mower to hand should the other one break down.