The subsequent chicory, yarrow, clover and grass mix produces remarkable results, with stock gaining 1.1-1.25kg of liveweight daily during their time on the farm. They are stocked at 1.5LU/ha, and only 4t of a supplementary feed is bought in annually to finish stock indoors. It is an organic pea/oat/barley mix that is grown locally.
"I make about eight or nine batches of baled silage every year. It's handy enough because we've our own kit and I can go out in the evenings after work and knock a few acres. It means that all our silage is over 70DMD, and good enough to keep cattle gaining weight," explains Duffy.
The chicory helps minimise the parasite burden, with calves getting a derogation for dosing only once during their first grazing season, and just before they are let out for their second season. But Mark must be careful to ensure that they have at least three times the standard withdrawal period before slaughter.
The only input the grassland gets is some slag every couple of years.
Duffy finds that sourcing certified organic stock is getting easier as the volume of stock grows and more marts host sales specially geared to the rapidly expanding sector.
"It's hard to buy in the lighter cattle at the right prices of say €2.65/kg, but there is always heavier stock available too," he said.
The number of organic producers more than doubled to nearly 900 when increased subsidy payments were announced in 2014. As a result, the land area has also doubled to 46,000ha.
However, the increase in organic producers is a concern for established producers such as Mark Duffy. Organic beef producers are able to secure prices
close to 25pc higher than conventional quotes at the moment.
Fertility is also key to making the most out of his grass, so Mark's calving interval of 371 days, with all heifers calving down at 24 months is a crucial element to making the system work.
But why does he bother with calving cows if he can just buy in the stock?
"It's always nice to have a couple of U grades in the mix to encourage the processor to do business with you," grins Duffy.
An impetus to make the enterprise as reliant as possible on grass has resulted in the Duffy's delivering 546kg/ha of beef, equating to sales of close to €4,500/ha.
From Ballybay to supermarket shelves in Dubai
The Duffys' success at beef was the reason that a local egg packer came knocking on their door two years ago.
"Nestbox had just landed a contract to supply organic eggs to Spinney's in Dubai, so they needed suppliers in a hurry. To put up a house with 3,000 birds you need about 7ac of organic grass for them to roam in. So not many farmers would have had that available," says Mark.
On the basis of industry averages, and a three-and-a-half-year fixed-price and index-linked contract, Mark estimated that he could have the €220,000 investment in a poultry house paid off in less than 10 years, but there was serious pressure to get it up in time.
"We were still nailing down the roof when the birds arrived, but thankfully we got it all going in time," remarks Duffy 12 months on.
Contrary to popular belief, he finds that the hens use every metre of the 7ac available to them.
"They graze out the grass nearest the house first. They'll go for the chicory and yarrow first, followed by the clover and then the grass. But when they develop a taste for it they'll keep coming out further and further into the field."
The 7ac is divided in four paddocks, with the birds able to graze 50pc of it any one time, while the other half is rested and reseeded.
"The area closest to the house is picked bare, but I can take a cut of silage off the furthest bits," he says.
Mark has hired a local man to help him for 10 hours a week with the 3.5hrs per day of chores required with the egg enterprise.
Meanwhile, he has recently recommenced full-time work as an electrician with nearby Lakeland Dairies, while his wife Grainne has left her job at Kingspan to help manage on the farm.
Despite mixing off-farm work with a busy farm, the Duffys have embarked on another major expansion in their egg enterprise.
"Nestbox brought down their customer from Dubai here one day a few months ago, and were so impressed that they turned around afterwards looking for me to invest in another 6,000 layers. I was barely a year into production, but all of our figures are in the top 10pc of what would be expected for free-range birds. Our hens are eating up to 10pc less feed because they are getting so much from the grass.
"In fact, I'm going to trial offering them silage during the winter months to keep their grass intake up. There are farms doing this in England and I spend a lot of time on line researching what the latest thinking is in organic poultry production.
"But I think the time they spend out grazing really helps their health. My flock's laying rate hasn't dropped much at all yet, even though they are nearly coming to the end of their standard laying life.
"This might allow me to keep the birds longer than the age that they would normally be culled at. They are also producing bigger eggs," explains Mark matter-of-factly.
But the canny business man wasn't going to be wooed on just by the feel-good buzz from his good output.
"We've secured another contract for the new houses that locks in a margin for a sizeable part of the pay-back period for the loan on the new houses. So the future looks bright at the moment."