Something is missing here from these posts. Under technical conditions - i.e. if you are harnessed and roped in, or if you are wearing crampons, or on any snow slope ~40 degrees or more, no dog will understand the meaning of belay, assuming that you could effectively belay them. And remember also that because the ecological niche that their canis ancestors occupied was as a predator capable of pursuing larger game by skimming over the surface of crusted snow, their paws evolved into a remarkable design that minimizes the chance of breaking through a crust as easily as whatever they were pursuing - which has an obvious downside that allows them to slide more easily on a moderate slope. This is very stressful for the animal.
My 7 year old female Siberian is clearly well equipped for winter conditions, is conditioned for climbing and altitude, has the trademark Siberian black mask over her eyes, with white under (which I agree helps with snow blindness), respects exposure and in fact shys away from it, and in fact has summitted St. Helens with me. But I wouldn't try to do anything technical with her, because I've noted while hiking open slopes in Mt. Hood forest that if she senses marginal traction underfoot, she panics and wants to run to a vegetable belay, where she knows she can get traction.
There are many other reasons not to put a dog through this situation, e.g. they don't know self-arrest, they don't understand "rock", they might get stepped on by a cramponed boot, they might pull on a rope at the wrong time, etc. - but this is the main reason. I don't want to expose her to this kind of stress and risk, so she stays behind when I go on technical climbs.
