In the 1st episode of season 6 of Game of Thrones, what happened to the hounds used by the search party when Brienne of Tarth came to rescue Sansa? They were there for a moment and then disappeared. The dogs should have at least tried to attack Sansa or Brienne.
Those were rescue hounds, not the same kind of dogs Bolton used last season to chase down and kill his target. The dogs most likely got frightened and decided to bail since their trainers just got killed by a large intimidating soldier (Brienne).
Remember, Bolton needed Sansa alive, Bolton never would have sent dogs to find and kill her.
The dogs' mission was to find them, which they certainly did. Maybe the dogs, happy with their findings, decided to go back to their owner and get their "good boys" steaks. We won't know for sure what happened to them, maybe in a future episode they will address this matter but for now we can only assume they ran away after the fight.
The continuity is even worse than the dogs disappearing... these are not the same hounds at all, Rasmey's "girls" that appear in the other episodes and then again tonight in Episode 2 are some kind of mastiff or pit bull type breed and do a VERY good job of acting vicious like they would tear someone to pieces. The ones in Episode 1 last week are clearly a totally different breed... bloodhounds. Which don't have a mean bone in the body, and didn't act at ALL like they wanted to hurt Sansa, their barking as well doesn't have nearly the same scary "rip you apart" tone to it. Yet Theon's remarks seem to make it out like we are supposed to think these are the same hounds that Ramsay uses in his hunts. They so clearly weren't I found it very distracting to that scene.
Last time seen in the show they stood there with the two dog handlers watching the fight:
Then, one of the dog handlers came to help. He attacked Podrick (after Podrick killed one of the Boltons). The other dog handler was the only survivor (five Bolton men died in total) and he apparently disappeared with the dogs after the fight. Apparently, he didn't even report to the Boltons, as in the next episode, Karstark reports to Boltons "We came upon the bodies on our way here."
Hard to say if this was intended or if the writers (D&D) didn't pay so much attention to this detail of the story...