Rooster crowing but no sound comes out

Hi. This is my Japanese Bantam named Golden. He’s around two years old. I have around 20 roosters. Golden is being bullied for quite sometimes now. He’s always hiding so I never noticed anything wrong with him. Until recently, it appears that when he crows, no sound came out. His comb appears more purple. But he’s i terested in hens. He eats normally. When I caught him, he opens his mouth to breathe like he’s panting. In this photo, he’s just resting separately because I want him to get enough food. He opens his mouth slightly to breathe. His tail is still looking upwards. His comb turns red after eating. I don’t know whats wrong with him.