For those of you that care for feral cats is there anything beyond food that you give them routinely to boost the immune system, specifically something that you could add to the food that would be accepted. In March, the feral that I feed had a bad respiratory infection, I noticed he was coughing and it developed into nasty eye and nasal discharge, he disappeared for 4 days and I thought for sure he had died but then he reappeared and things had improved and he gradually recovered. Winter is coming where I am and I want to do what I can to help him be as healthy as possible. I have tried to trap him without success, he will not allow me to get any closer than about 10 feet from him, unless my storm door is between us, so touching is out of the question and my vet will not dispense medication without having examined the cat, so should he become ill again I would not be able to get him any medication, so I want to do what I can to make sure he is as healthy as possible.