UPDATE, summer 2021
Starting January 1, 2022 the law will change the mandatory training not only for big dogs, but for all dogs, living in canton Zurich:
§ 7. 1 Anyone who keeps a dog must attend a recognized practical dog training with the dog.
§ 7. 2 Every first time dog owner must also attend a recognized theoretical dog training course.
UPDATE, February 10, 2019
The voters of canton Zurich decided to keep mandatory dog training.
When arriving in the canton of Zurich, pooches belonging to breed type I (bigger than 45 cm or heavier than 16 kg) need to visit different classes, depending on fido’s age.