He's bored with kibbles. Like human, dogs also get bored when fed one thing again and again. Try to feed different things to him like curd, rice with curd, eggs, raw meat, etc. If you want to continue feeding him kibbles then try to mix it with wet dog foods, some of them I know are Pedigree's chicken and liver gravy and Dr. Aulder's duck gravy. I'm sure he would have it more happily. If he's loosing his appetite, consider giving him a good liver supplement but first show him to a good Vet.