I'm pretty sure some of the dogs have mentioned having mothers, we just don't see any females in this game because... fan-service? For some reason, every single dog in Shelter seems to be unabashedly homosexual and have rampant sexual tension with each other, with not a female in sight. After all, for all the great worldbuilding and story-telling Raus has done, a large part of this game's purpose is to have horny dogs talk about (and do) gay sex.
As part of the target demographic, I'm not exactly complaining... but it's very odd from a worldbuilding perspective. There are women in this universe, I guess they're just... banned from Shelter? Maybe it's a population control thing so Shelter doesn't become too crowded? Maybe all dogs are misogynists. I'm not sure Raus expected us to think about it or really care. Maybe he himself didn't even notice.