Our chickens have never been too keen on the snow, either. They really like having a covered run. The pictures of your run looked like you'd need to add a supporting structure, to be able to add any cover. Can you do something like curve a cattle panel over their run, next to the coop? Then tarp it? You might get lucky and either the aggressors or the victims might spend more time outside.
I know this is a longer term problem for you. What have you already tried? I'd give them as much to do as possible. Hanging cabbages, pots of grass that you start in the house and take out to them, any kind of veggie scraps to peck at. Things like suet cages can be hung up with greens or veggie scraps in them. Scatter sunflower seeds, so they can spend time scratching around for them. Give them a dust bath of sand to dig and scratch around in.
Since your coop is so big, can you do anything to break up the visual space a bit? Add some shelves that chickens can get up on? Put an old table in there? If you can do that in front of a window, they'll spend time looking out the window, too. Can you make something like a mini room divider? You want chickens to be able to get away from each other or out of sight, without getting cornered. Hopefully, the aggressors might get busy and forget to go pick on the others, if they can't see them.
If you haven't done it already, I'd add an additional feeder and waterer. Even if it's just small bowls.
Have you tried the Avia Charge? That would be good for them. I'd definitely try adding some sunflower seed to their diet, also. Plus some greens.
There are peepers you can get, that clip on and prevent the bird from seeing straight ahead. Also, rings that clip on and keep the bird from closing it's beak all the way. They can still scoop up food and water with their lower beak.
Also, you can clip just the tip of their top beak. The beak grows similar to your own fingernails or your dog's nails. You don't want to cut the beak off back into the live tissue, as that's painful and can cause permanent damage, like the commercial places do. It's no problem and not painful at all, to just clip the tip of their top beak back, though. It would keep them from doing as much damage.
Good luck with your flock. This is such a heartbreaking problem. I hope you can find a combination of things that helps.
I know this is a longer term problem for you. What have you already tried? I'd give them as much to do as possible. Hanging cabbages, pots of grass that you start in the house and take out to them, any kind of veggie scraps to peck at. Things like suet cages can be hung up with greens or veggie scraps in them. Scatter sunflower seeds, so they can spend time scratching around for them. Give them a dust bath of sand to dig and scratch around in.
Since your coop is so big, can you do anything to break up the visual space a bit? Add some shelves that chickens can get up on? Put an old table in there? If you can do that in front of a window, they'll spend time looking out the window, too. Can you make something like a mini room divider? You want chickens to be able to get away from each other or out of sight, without getting cornered. Hopefully, the aggressors might get busy and forget to go pick on the others, if they can't see them.
If you haven't done it already, I'd add an additional feeder and waterer. Even if it's just small bowls.
Have you tried the Avia Charge? That would be good for them. I'd definitely try adding some sunflower seed to their diet, also. Plus some greens.
There are peepers you can get, that clip on and prevent the bird from seeing straight ahead. Also, rings that clip on and keep the bird from closing it's beak all the way. They can still scoop up food and water with their lower beak.
Also, you can clip just the tip of their top beak. The beak grows similar to your own fingernails or your dog's nails. You don't want to cut the beak off back into the live tissue, as that's painful and can cause permanent damage, like the commercial places do. It's no problem and not painful at all, to just clip the tip of their top beak back, though. It would keep them from doing as much damage.
Good luck with your flock. This is such a heartbreaking problem. I hope you can find a combination of things that helps.