I purchased a large heated cat retreat for the cold weather, but one of our cats won't allow the others inside. We have six outdoor cats. While they have shelter from the elements, it still gets chilly.
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Calming Chews made by Sentry. Not in my store so I got them online. They really do mellow my wild cat. My gentleman cat thinks they are tasty and he's picky. There also sprays you can spray in the retreat.
do not force pets! allow him/her to get comfortable. it takes time! keep their box clean and make sure their water is fresh!
Catnip, silvervine, thyme, valerian root can help calm cats. One of my cats is especially anxious and I give her HomeoPet Feline Anxiety Relief. There drops you put in their food. It might help with the hostility. But it sounds more like a territorial issue. You might want to have a small outdoor shelter just for that cat. If you don't want to buy another heated one, you could make one with 2 plastic bins, different sizes, and insulate it with Styrofoam. It's a cheaper option.
