When our Speckled Sussex Rooster Limpy broke his leg he went off his food also partly because he was confined after free ranging all the time bar night time. I found he loved eating either frozen or tinned Corn / Sweet corn, Peas, cooked or grated carrot and cold cooked potato, meal worms were also a big fave as was cooked fish or a can of Tuna, he even liked picking over the bones from the roast lamb. Broccoli was also another green that he liked as well as shredded cabbage leaves.
That was 2 yrs ago now and he's got a limp but he free ranges with the rest of the flock and has his 2 hens that stay with him. The other Roosters leave him alone as his brother Big Chick keeps an eye on him. He even manages to do the deed with his 2 hens and has produced me some nice pure bred chicks. he's a bit slower than the other birds but is so laid back we can just walk over n pick him up n carry him if we need to get him back in the coop quickly. He sure is one cool dude and his 2 hens adore him lol.