Real said in a statement on its website that tests had "found contents of horse meat" and that it had already taken the frozen lasagne off the shelves as a precautionary measure last Friday.
It added that there had been "at no time evidence of a hygienic risk for consumers" but that the product did not meet Real's standards of quality and it took the matter very seriously.
The group, which has 316 shops in Germany, said it was working closely with distributors and authorities to "take all necessary measures and ensure that only acceptable goods are sold to customers."
A spokesman for the Edeke chain said horse had been found in its Gut & Günstig Lasagne Bolognese, which was pulled from shelves only on Tuesday. Tests discovered five percent of the meat meant to be beef was actually horse.
German Consumer Affairs Minister Ilse Aigner said on public ARD television Thursday that "authorities must check to what extent horse meat is actually present in these products."
"Firms have already reacted and taken suspicious products off the market," she said.
Supermarket chains Kaisers Tengelmann and frozen goods chain Eismann are also testing their products. German officials announced Wednesday they suspected food may have been delivered to the country mislabelled as beef when it contained horse meat after being informed a day earlier via a European alert system.
The EU's executive called in Europe's law enforcers and urged bloc-wide DNA food testing on Wednesday to restore consumer confidence Britain, France and Switzerland have all found horse meat in frozen meals labelled as beef.
British Agriculture Minister David Heath said horse carcasses that tested positive for an equine drug that is potentially harmful to humans were sent from Britain to France and may have entered the food chain there.
But he said phenylbutazone, which can cause a serious blood disorder in humans in rare cases, had not been found in tests on products made by food giant Findus, which has been embroiled in the scandal.