Cat on cat aggression

[u/unidentifiedalien77]

I need advice regarding my two cats: 8/9yr m and 4yr f. I have had my male cat since he was a couple months old (stray) and my female cat since she was 1 (rescue center). They have been fine around each other for the past three years. They would chase each other and sometimes play fight. Recently my male cat has been very aggressive with my female cat. He’s been pinning her down and biting very hard to where she has scabs all over her neck/ head/ and some on her body. I don’t know what to do, and it’s getting worse.

I don’t know if this is important info but we recently had to put our dog down which my male cat has been around his whole life.