What makes a cow sound delicious and appetizing, yet substitute that for horse, and things go badly? 

The Food Safety Authority of Ireland has discovered traces of horse and pig DNA in packages marketed Beef patties. The manufacturer of the beef with the highest percentage of horse meat, Tesco, has pulled their name brand patties from stores in Britain and Ireland. During manufacture, the beef has seven ingredients added to the meat. The Irish Agriculture Department has found that one of them tested positive for horse DNA. 

The processing plant where the additive came from, is Silvercrest Foods.

Tesco is the world's fourth largest food retailer, and is known in the US under the brand Fresh & Easy. 

Tesco social media team had an extra bit of bad luck, when their scheduled tweet was released saying: 

It's sleepy time so we're off to hit the hay! see you at 8 am for more #TescoTweets