Rooster with a purple comb/He died any clue what caused it?

He was fine last night. They have fresh water, I did switch to pellet instead of crumbles 2 days ago, fancy scratch grains,cracked corn, and oats for treats. They are not free ranging due to dog issues but have plenty of space. He is a little less than a year old according to the lady who gave him to me.

No gasping, no sneazing, it does look like his poop as become a little runny though, he is drinking but not eating. I even dug him up worms and he is not eating. Unsteady on his feet and his comb is half purple already. He does have a small red mark at the back of his head.

Please tell me what to do next. I have him separated so the other can not hurt him, We are offering water and have him sitting in the shade. My husband is guarding him now. Help

Note: he died as I described below. When I picked him up a flow of yellow water came out. Not alot but maybe a teaspoon full. Very yellow. Is that what was wrong with him? What caused it? How do I protect my girls. I just picked up the apple cider vinegar yesterday and started it this afternoon ( a day late and a dollar short I know). No one is sneezing or act odd. Well the broody hen is odd but not odder than usual. Any opinions or advice would be lovely.

 

NO ideas? He was a bit thirsty when I offered cold water in a bowl. He has 2 waterers available to him all the time though. Not super thirsty. I checked for mites. I don't see anything. The back of his head has the little red mark and it looks like he's been pecked at. His poo is runny yellow.

Any ideas would be great. Right now he is hiding under a horse feeder and chilling out.

Also just in case I am missing the mites I want to treat them all. What kind of 7 dust is safe. I got a little can of power. 5% 7 dust that you use on veggies but it says to not use on or around animals.

 

He still has no discharge or sneezing but his breathing is labored and he can barely walk now. I cannot get him to drink. I did dust him a little bit, probalby not as well as I should have but he started breathing so heavy I was afraid I was killing him. His comb is getting darker and everything is taking on a very very deep red to dark purple. I don't think he is going to make it. He was fine eating, drinking, and hoping on hens last night. I can't get him to eat or drink though.

 

He wasn't good, He stood up, walked a couple feet, tucked his head to his chest and fell over dead right in front of us. I ran too him when he tucked his head in and he was dead before I got to him. Very upset. Doesn't help having a dozen buzzards circling the chicken coop all morning. We had him in the shade under the plum tree sitting next to us while we worked the garden so we could watch him. He wasn't even 20 feet away and he died that fast. No gasp, no nothing, just tucked in his head and fell over.

 

So upset. He was just a free rooster someone was going to let loose in the woods to fend for himself. I got him and his buddy who stopped being his buddy when we bought them some hen company. He was such a good rooster too. He was meaner than anything to the other roo and to me if I got his hens upset but he sang to them when they laid eggs and scratched up bugs for them. Very upsetting.