Feeding your cats with boiled chicken meat is one way of fattening up your cat. Another way is feeding them with kitten food which is high in protein. Like Suhaimy said, nutering or spaying your cat will also make them fat
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For shiny coat, I usually feed my cats with skin and coat supplement e.g. fish oil which is high in Omega 3 and 6. Also good for the cats immune system.
