Sick rooster, please help! (with pics)

[FlippingTheBird]

I got this 8 month old FBCM roo a few weeks ago, and the poor little dude was acting a little under the weather so I checked him out and discovered feather louse! I treated him and the louse are gone but I started noticing he would sometimes still act sick and go take random mini naps - even tucking his head under his wing and poofing up a tiny bit, or standing in one area with his eyes closed, hunched up and poofy, the typical sick bird symptoms. But then he'd get up, go scratch around, eat, drink and dust bathe and act like a normal chicken, but then act sick again. The louse were gone, so I wasn't sure what could be making him like this.

After checking him a bit, I noticed he had this foul smelling nasty gunk around his vent. But his poop is completely normal, no diarrhea or weird colors or bloody bits or anything, it's just this bit of goopy stuff hanging around his vent. He's lost a bit of weight, and his sternum is prominent, even though he still eats and drinks, which makes me think it might be worms? I don't know what's going on, or what I should treat him with...should I pump him full of probiotics and electrolytes, some apple cider vinegar? Or tetracycline? Corid, wazine? All of the above or only a combination of something? I know vitamins can cancel out tetracycline, but I'm not sure about the others. I just don't know what to do, I'm so unfamiliar with sick birds and medications...

I'd like some input, he's such a cool, mellow little dude, he'll even jump in my lap and I'd hate to lose him :/

Here are some pictures of his vent, sorry they're not the best:

 

[Eggcessive]

Bring him inside for 24 hours, and wash his vent feathers with soap and water. Start using probiotics in his water 2-3 days a week. For a few days, you can use some vitamins and electrolytes in his water. Rooster Booster has a brand Vitamins with Lactobacillus that includes all 3. Make sure that his water is kept clean and fresh. Some chickens can get a fungal infection called vent gleet that can scald their vent area and cause infection of the digestive system. He may not have that, but I would only feed him chicken feed, clean water and nothing else. Make sure that others aren't keeping him from food and water which is a common cause of weight loss. If your feedstore carries Valbazen sheep and cattle wormer, give him 1/2 -3/4 ml orally (shake well) and repeat in 10 days. If you can only find SafeGuard Liquid Goat Wormer or horse paste, then give him 1 1/2 ml daily by mouth for 5 days straight.