In order to ease the commerce of agricultural products and access to the more than 500 million people in the European market, Switzerland has signed bilateral accords with the EU in the veterinary sector, among which the same sanitary regulations for animal disease exist. For that reason, the EU requested that Switzerland ban the use of swill in pig feed.
(Original in French. Read Google translation here).
http://bvet.kaywa.ch/fr/maladies-animales/aliments-liquides-pour-porcs-retour-sur-une-longue-histoire.html