TULLAMORE - Brexit hung like a cloud over Ireland's biggest agricultural fair this week, with the country's food and farming industries, heavily reliant on their British neighbour, feeling the impact already.

Nearly 300,000 people visited the 2017 National Ploughing Championships outside Tullamore in the central County Offaly. Their boots quickly churning up the muddy fields, visitors were keen to trade talk of farm machinery and production volumes.

The annual gathering was also an occasion for families to see the animals, play the Irish sport of hurling and soak up the festive atmosphere.

However, for the exhibitors, the atmosphere is somewhat weighed down by Britain's looming departure from the European Union and the slide of its sterling currency, which has made Irish exports over its only border exceedingly expensive.

John Keena, a cattle breeder, wears a stern face when talking about the 20 percent fall in sterling against the euro, since Britain's vote in June 2016 to leave the EU.

"Meat factories maybe are taking full advantage of Brexit, like they have dropped the prices in the last six weeks by something like 30 cents the kilo. We think it's unjustified and that we should be back at four euros the kilo," he said.

Economic ties between Britain and Ireland -- which was part of the UK before independence in the 1920s -- are particularly strong. The Irish pound, replaced by the euro in 2002, was linked to sterling until the late 1970s.

- 37 percent of agri-food exports -

Joe Healy, president of the Irish Farmers' Association, in-between selfies and chomps on his muffin, expressed concern about Brexit.

"We export 90 percent of our beef. Fifty percent of that goes to the UK, 45 percent to Europe and five percent onto international markets," he said.

"But of the 45 percent that goes to Europe, half of that uses the UK as a land bridge to get to the European market," said Healy, underlining the sector's dependence on its nearest neighbour.

Like beef, Ireland's agri-food sector -- the biggest employer in the republic with 8.4 percent of the workforce -- exports 37 percent of its production to Britain.

The mushroom industry, which sends 80 percent of its production, has felt the pinch of the fluctuating pound, with already narrow margins tightening further and driving several operators into bankruptcy.

Farmers, breeders and processors are also anxiously awaiting the outcome of London's negotiations with Brussels, fearing a return of customs barriers between Britain and the EU.

"What we're trying to do is plan for the worst and hope for the best," said Tara McCarthy, the chief executive of Bord Bia, the government's state food agency which has provided exporting companies with information and marketing tools to help them come up with new strategies to cope with the situation.

- Cheddar cheese threat -

Dublin is also looking for new destinations if Britain leaves the EU without a trade deal.

"The gap would be huge in the worst case scenario -- we're talking about 250,000 tons of beef," said McCarthy.

The country is eyeing up China in particular.

"We don't have access yet but the Chinese market would be a huge opportunity", McCarthy said.

Unlike the meat and mushroom sectors, milk producers are better off thanks to a recent rise in dairy prices after a tough 2016, according to John Wicherley, a dairy farmer from County Cork in the southwest of Ireland.

The situation is "stable", he said, revealing he was "cautiously confident".

His cows produce milk for the Irish cheese industry, which provides 80 percent of the cheddar eaten in Britain.

"Without the UK for our cheddar cheese there isn't really a market," Healy said of Britain leaving the European customs union.

"Like farmers and processors, we've all invested a lot in producing the type of product that the UK market and the UK customers require."

Without easy access to the UK market, the Irish food producing industry looks particularly vulnerable.