SR 455.1, the Tierschutzverordnung (TSchV) addresses appropriate social contact, movement, and kenneling conditions for dogs. Articles 70, Sozialkontakt, Art 71 Bewegung, and Art 72, Unterkunft und Boden are among the relevant bits and bobs of the legislation. Also Table 10 of the Anhang, page 113, lays out minimum space requirements.
https://fedlex.data.admin.ch/filesto...4-de-pdf-a.pdf
If you believe that the dog is being mistreated:
If there is not immediate mortal danger, make a report to the cantonal Veterinäramt. I am not sure if you can report anonymously, or if you need to leave your name.
If an animal is in mortal danger, call the police in the first instance.
If the animal is in immediate mortal danger and you believe in good faith that the animal will die before the police arrive, you may take limited steps, but it is always wisest, and in your interest to protect you from accusations, to tell the police what steps you will take, get their permission, and enlist witnesses. This applies to situations like a dog locked in a boiling hot car, unable to breathe.
If you are unsure if the way the dog is being kept conforms to the TSchV, you might write the Tier Im Recht for advice on the legalities, here:
https://www.tierimrecht.org/de/recht/rechtsauskunfte/
They cannot advise on individual cases, but might be able to better explain the general relevant laws.
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Switzerland has some of the best animal protection legislation on the books... but unfortunately enforcement is not always what one would like to see, and resources behind enforcement are not always available.
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Thanks for looking out for this poor dog. It gladdens my heart to see people who care.