"John fed 3.5t of meal per cow from April to September in 2012 because there was literally no silage left in the pit from May 1," explained local Teagasc dairy advisor, Ger Courtney.
"His feed costs per litre of milk have been running at 8c/l, but John hopes to bring that back to 4c/l following the work he has done here," said Mr Courtney.
With 32mm of rain falling the night before, visitors were pleasantly surprised by how trafficable conditions were on the day. Teagasc research states that every millimetre of rain is the equivalent of an additional 10,000 litres of water per hectare, so drains in the entire southwest were working hard last week.
There has been a huge amount of interest and activity around drainage on farms over the last 12 months, but Teagasc advisors were keen to stress the importance of getting such a significant investment right from the start.
"There is no 'one size fits all'," Johnstown drainage researcher Owen Fenton told farmers attending the open day.
"The era when you just went along with what the local contractor had done for everybody else in the area is over. You may be able to get away with putting your drains in at 0.8m, but you may also need to go down to 1.5m or deeper to get your drains in a layer of the soil where they are able to work most efficiently."
Farmers were urged to dig 2.5m test holes in various areas around their proposed drainage site.
"This will allow you to assess what type of soil you have and, from the seepage, identify if and where a permeable layer lies in the soil profile," said Moorepark's Pat Tuohy.
"If there is no free draining layer, then you have to improve what's there by a combination of ripping, moling and sub-soiling.
"Whether you need to use gravel in your moles depends on how stoney your soil is. If the ground is naturally very stoney, the moles won't last without a filler of gravel."
Mr Tuohy also urged farmers to be cautious regarding the claims surrounding some recent drainage innovations.
"The Connacht Agri pipe claims that it does not need any stone around it, which, let's just say, is a very grand claim indeed," Mr Tuohy told farmers.
"The old system of laying straw or reeds between the pipe and the stone certainly has its merits. But any system will eventually block up with sediment over time."
Owen Fenton urged farmers to target the permeable layer of soil with their drains, even if it went against the natural fall of the field.
"The soil is like a big pump, and water will find its way into that drain, even if it has to come up to it," insisted the Teagasc specialist.
However, Mr Fenton also advised farmers that the first and cheapest step in any drainage programme was to clean out and deepen any existing open drains.
"Get them down to a level where you start to see water seeping in," he said.
James O'Loughlin, who is co-ordinating the Heavy Soils Programme for Teagasc, also cautioned farmers on the damage that reckless management could cause in a very short period on even the best drainage systems.
"Leaving a herd of cows out in a freshly drained field on a night like last night (when 32mm of rain fell) could literally break down all the work of rippers, mole ploughs and sub-soiling.
"So you have to mind it. Very often, you will need to come back in 15 years later and maybe start all over again, but against that, I've seen drains in perfect working order after 25 years," said Mr O'Loughlin.
He also noted that farmers looking to spread the cost of a drainage programme over a period of time could do some of the work in steps.
"The addition of the gravel to the mole drains really added up because the stone is almost twice as expensive as standard 50mm drainage stone. But it can be retrofitted to mole drains in later years.
"In addition, farmers should pay a lot of attention to the shape of the drains that they are creating.
"On one hand, you don't want them so narrow that the side-walls are collapsing, but the wider you go the more you spend on stone.
"Our advice is that you create a V-shaped opening for the first foot or two, but then switch to a narrow tile bucket for the bottom part. Filling the drain up to the surface with stone is another way of using an awful lot of stone and increasing the risk of nutrient run-off, so it's not recommended," he said.
Speakers on the day also emphasised the ancillary costs that farmers should consider when embarking on a drainage programme.
"There's no point in spending a lot on good drainage if your soil fertility isn't right," explained soil expert David Wall.
"It is a big challenge to improve fertility in heavy soils, but the upside is that when you do get the fertility up, these soils tend to remain that way because the nutrients are harder to wash out of them," he said.
Soil tests on Mr O'Sullivan's farm revealed that 90pc of the farm was sub-optimal for soil pH and more than 60pc was deficient in both phosphorus (P) and potassium (K). These low values appear to be typical of farms in the region.
"The real value of slurry is more so what it provides in terms of Ps and Ks rather than nitrogen, so farmers should really be targeting their low index fields with their slurry."
Mr O'Sullivan also acknowledged that he will have to invest further in roadways and water troughs and piping to maximise the benefits of the extra grass that his farm is already starting to grow.
"But I don't think that this will be a major extra cost. A few new troughs and a bit of extra piping to bring them further down the field won't come to a lot. I only need a few short spurs off the lanes to access the fields and they can be put in with shale pencil at about €100 per load."