Shares in Greencore have plummeted by around 22% this morning.
The share-price fall comes after the British supermarket chain Asda confirmed it had withdrawn a beef bolognese sauce containing horse DNA which was supplied by Greencore.
Greencore said the meat was supplied to it by the ABP Food Group's Nenagh plant in Co Tipperary.
Greencore is run by Patrick Coveney, the brother of the Agriculture Minister Simon Coveney.
Editor of the Irish Farmers Journal Matt Dempsey said: "It's embarrassing (for the Minister) and he'd rather it didn’t happen, but I don’t think it will create any particular difficulties.
"Nobody is pretending that Patrick Coveney would have known, even remotely, that (Greencore) were buying dodgy ingredients like this.
"I think the Minister will say it's unfortunate, but also that it shows how even-handed we are that even the Minister's brother's firm is not exempt from close supervision and publication of the (test) results."