Fane Valley has acquired Donegal company Robert Smyth & Sons Ltd, which trades as Smyths Daleside Animal Feeds.
Smyths Daleside Feeds specialises in animal feed products and nutrition from its base in Ballindrait, Co Donegal, just across the border from Strabane.
The deal, which is subject to approval from the Republic's Competition and Consumer Protection Commission, will see Smyths' operations, including Burke Shipping Services at Lisahally Port incorporated into Fane Valley.
The co-operative group includes firms such as Linden Foods and porridge maker White's Oats.
Group chief executive Trevor Lockhart said the acquisition was "a natural fit" for Fane Valley, presenting an opportunity for the co-op to further extend its catchment area.
"The company will continue to trade under the Smyths Daleside name and day-to-day operational responsibility will remain with local management and staff.
"Customers can therefore be assured of a 'business as usual' approach in their dealings with the company going forward."