It comes after Irish authorities detected burgers containing horsemeat in 2013
European police are said to have dismantled an organised crime group that was trading horsemeat "unfit for human consumption".
The Spanish police led the operation, with the assistance of Europol.
They worked in coordination with authorities in Belgium, France, Italy, Portugal, Romania, Switzerland and the UK.
A total of 65 people have been arrested and charged in Spain, with charges including animal abuse, money laundering and crimes against public health.
The investigation began in 2013 after authorities in Ireland discovered beefburgers containing horsemeat.
The discovery led to a major scandal, with retailers in Ireland and across Europe withdrawing products from shelves.
In a statement released today, Europol said: "In the summer of 2016, [Spain's] Guardia Civil’s Environmental Protection Service initiated Operation Gazel after unusual behaviour was detected in horsemeat markets. They detected a scam whereby horses in bad shape, too old or simply labelled as 'not suitable for consumption' were being slaughtered in two different slaughterhouses.
"During the investigation, Guardia Civil was able to locate the Dutch businessman related to the Irish case of the beefburgers containing horse meat, in Calpe, Alicante. From there he led the activities of the organisation, putting his most trusted men in charge in every country affected by the scam."
The main suspect in the case was later arrested in Belgium, Europol added.