We acquired a neutered tomcat last summer by virtue of him deciding he wanted to eat the food of my other cats when the doors were open, and then just move in permanently. He's about 2.5-3 years old and a large framed cat. In September, he weighed 6.2kg but is now nearer to 7kg and feels quite portly in spite of his bodyframe.
He is fed the same as my other neutered tomcat who weighs 4.3kg. They all have microchip cat feeders so I know what they are having to eat inside. However, I know that the new cat is a hunter who eats what he catches if he can, and he also goes into the house of at least one neighbour to eat their cats' food - and this is not encouraged behaviour so a collar saying "don't feed me" wouldn't be much help.
Any ideas on how to put him on a diet? One of my girls is on Hills Metabolic to lose some weight (because she kept pinching everybody else's food - hence they all have microchip cat feeders now) and it's slowly working but she's not hunting or scrounging. I tried him on it, but it coincided with a killing spree so I think he was taking matters into his own paws. Keeping him inside isn't an option.