The European police agency Europol said 65 people were arrested in Spain, and the main suspect, a Dutch citizen, was arrested in Belgium.
"In Spain, 65 people were arrested and charged with crimes such as animal abuse, document forgery, perverting the course of justice, crimes against public health, money laundering and being part of a criminal organisation," it said in a statement.
An EU investigation revealed that less than 5 percent of all beef products tested had come back positive for horse DNA.