Can't be exact from the photos, but it is definitely one of the
Lactarius "Milkcap" species. The milk from most of these is acrid to the taste.
If these are the actual ones that your dog had, then he obviously didn't have chance to eat any - and he would probably have spat them out anyway, as the taste of the milk is - err, not pleasant.
(Fungi fans usually taste & then spit out the milk as one of the identification aids), so I wouldn't worry too much.
Regards,
Mike.