Hi! Mario has a weird looking gash next to his rectum. I haven’t noticed till now and was wondering could it have been from something outside or is it something serious? I have antibacterial cat wound spray should I spray it?
Ouch! it's possible that Mario has been licking or chewing the spot, which is why there is a cut there now. I would definitely keep the area clean and dry and place an Elizabethan (cone) collar on him so he can't lick the wound or the wound spray you place on it. I'd also look for any signs of irritation in addition such as parasites, red skin indicating allergies, etc that may help you determine what caused the wound.
If the area is very bothersome, is affecting his ability to go potty, or it's hot to the touch, growing in size, or oozing pus or debris, then it is best to seek out veterinary care in person as they can indicate something more serious such as an infection or injury to the anal glands/rectum that needs treatment.