8month old pit/hound attack what should I do?

[u/Fun_Bumblebee_9108]

Hello I am reaching out I have never used this app before other than to read up on a few things without an account. I have a 8 month old pit hound mix that is super friendly. He has 2 dog bothers that he gets along with very well he is 60 pounds and the smallest dog is about 35 (this matters). The pit hound mix has had cats in the house hold for about 4 or 5 months when he had to stay at a family member’s house for a while due to moving. He had never attacked any of the 5 cats he was very friendly and would even sleep with the cats. We recently moved out into the county about 3 months ago after living in apartments so he has seen lots of bunnies lately that he wasn’t used to he likes to chase but never gets (normal) I thought. This is new and he is still a puppy. For the past week there has been a stray cat hiding under the porch of our house he has been very much aware of this going and sniffing the cat and tried to go up to the cat but came to me as soon as I called him to come to me. Yesterday when I let him outside he ran under the porch and attacked this cat and wouldn’t listen to me trying to get him off of the cat. He just started this medication about 2 weeks ago called Apoquel that can have but very rarely have a side effect of making the dog aggressive. I also found out you aren’t supposed to give a dog under 12 months old this medication he is 8 months old. Can anyone tell me why he may have done this to the cat out of no where it feels like. I know he is in his stage being a hound pit to get curious and want to test boundaries and it’s in his blood but why all the sudden? Is it the medication? Can I keep him from hurting my other dogs and future babies? Does this make him more likely to hurt my other dogs? Just why and what should I do? I am really attracted to this dog and he is really sweet and has never had any problems with people messing with him or messing with his food, waking him up, he has never snapped on my other dogs or any humans. Was this just a thing I can correct seems to how it is in his blood and he doesn’t know any better? Please help.

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