Have you been giving him any grit? Chickens need grit to grind up their food since they have no teeth.
If you don't have any, take him outside & let him peck around in the dirt. Hopefully he will find some.
Grit:
Ever heard the saying "scarce as a hen's teeth"? That's right, chickens don't have them! Instead they eat tiny pebbles and store them in their "crop". When the food enters their crop, the pebbles grind it up to make digestion easier. For baby chicks, sand, parakeet gravel or canary gravel, available at your local pet store or grocery store pet aisle, will suffice. You can either sprinkle this in their feed or provide it in a small cup or bowl.
Link: http://www.mypetchicken.com/backyard-chickens/chicken-care/chapter-4-caring-for-baby-chicks.aspx
The chicks were freeroaming before we got them, and I let them out every day for an hour or so. Also they've been spending the whole day outside in their coop that has a run since tuesday, and it was only until Thursday that I saw Rusty having problems eating. Before that none of them showed me any signs. then again i made the mistake of mixing adult feed with their food, and while they other two chicks are doing well, Rusty is having issues. I gave it boiled egg to Rusty again, and it ate a lot, but it seems to bother him a bit to swallow. the more I watch it, I think there is a problem with its mouth, something seems to bother it when it eats
Seeing how Rusty is doing, I think it can hang in there until Monday. I have that day off so I can go buy some parakeet gravel at petsmart. I hope they sell it. I also hope this feed store opens tomorrow. They have store hours, but they don't seem to stick to them, and for sure they don't open on Monday, so I'm gonna call from work, and if it's open, then I'll ask my sister to go buy the food. I brought the other two chicks inside tonight and gave everybody a tortilla soaked in warm water. They ate it, and rusty even tried to steal some food from Godzilla, the biggest chick. So at least rusty is behaving almost normal, except for the bad breath, shaking its head when it eats something that seems to bother it, and then stand still, get a bit puffy, and cose its eyes as if it's sleeping.
This chick is giving me a headache
. I wish I had been better prepared to take care of it.
I checked on Rusty this morning. Still no change, the crop empties and it pooped, the poop was a bit foamy and mostly white. I felt a hard item in his crop, and he has still rather foul beath. That opject feels like a pebble, I wonder if that's the problem? How can I help Rusty pass that thing, or get it out?
The other two are fine, the just smell like chicken and are acting normal. I know Rusty's crop empties because I gave it food last night and the crop is smaller today. I've been reading about sour crop, but I'm scared of trying to make him vomit, what if I do it wrong?
This should help his sour crop & his saliva/mucus problem.
To treat sour crop:
ASTRINGENT SOLUTION
This solution can be used to treat young birds that show non-typical disease symptoms of poor growth. The solution can also be given to birds suffering from respiratory diseases that produce a large amount of mucus exudate. This solution will help "cut through" the mucus and allow it to be expelled easier.
Two quarts of organic, unpasteurized apple cider vinegar diluted into 100 gallons of water
(4 teaspoons/gallon)
The tannin in the apple cider vinegar aide in removing any mucus or coating from the mouth, throat, or intestinal tract. Nutrients and drugs are more readily absorbed. Offer this solution as the only drinking water source for two to three day intervals.