Wow Leon, sorry no one has replied to this...
I've (THANKFULLY) never had a sick Guinea in all my years that I've raised/kept them... so all I can suggest is to maybe try to get it to drink some water with poultry electrolytes and vitamins in it (or even clear pedialyte) and offer it some of it's favorite treats just to get it to eat something. If it does ok with the water, you may even want to make a thin mash/slurry of high protein starter feed and try to get some of that into the bird too. Be careful not to choke the bird with the mash, don't force it, especially if it is weak, electrolytes a few drops at a time would be better to try first if the bird is already too weak to deal with any food in it's mouth. Check the crop, make sure it's not impacted with grass, or shavings or anything like that. Feel the breast bone and make sure it's not overly thin from being kept from the food by the others, and also check for injuries ad bruises. Keeping it warm is most definitely a good thing, but I would isolate it in a cage or crate so the others can't pick on it or stress it any more than it already is. Hopefully it pulls thru. Sorry you have to deal with a sick bird that you've raised from a baby, I know it's hard to deal with. Good luck with it!
