The operation was coordinated with police in Belgium, France, Italy, Portugal, Romania, Switzerland and Britain.
The suspects are facing an ongoing criminal investigation led by a court in the northern town of Ponferrada, in the Spanish province of León, into alleged animal cruelty, forgery, money laundering, membership of a criminal organisation and a crime against public health.
The Dutch suspect oversaw operations from Alicante, Spain, and had a network of "his most trusted men in charge in every country affected by the scam".
Investigators found the meat to contain the anti-inflammatory drug phenylbutazone.
The spokesman explained that officers launched a full-scale probe, called Operation Gazel, after detecting "atypical signs in the horse meat trade" previous year.
An unidentified Dutch businessman arrested in Belgium is suspected of controlling the illegal trade from southwest Spain.
As a result of these arrests, several bank accounts and properties were blocked or seized, and five luxury cars seized.
Investigators looking into "unusual behavior" in horse meat markets are said to have uncovered an operation run by an organized crime syndicate in Spain in which old and neglected horses were slaughtered and sold as meat overseas.
How did the racket work?
'The meat was distributed in different ways but mainly sent to Belgium, the largest exporter of horse meat throughout the European Union, ' said a police spokesman.
The spokesman claimed that the organisation changed the identify of the horses by substituting their microchips or falsifying animal passports.
After analyzing samples of the meat found in the Spanish slaughterhouses, investigators concluded that the meat was mostly sold overseas.
One of the charges brought is animal abuse but details are not yet available.
According to that report, Italy imported 21,693 tonnes and France 11,898 in 2012, while Belgium was the chief exporter, shipping 17,320 tonnes.
Total EU horsemeat imports in 2012 came to 50,250 tonnes and exports 54,853, while EU beef imports in 2011 totalled 315,000 tonnes and exports - 510,200.