My chick is experiencing retarded growth

[Luckybaby]

When the chick is 4 to 5 weeks old, I noticed that it has few ruffled feathers, it's wings is a little droppy and it usually close it's eyes. I put anti-coccidiosis medication including the ones with ethopabate, when it was 3 weeks old, and it eating medicated broiler starter feed since it was about 5 weeks old. However, the symptoms still exist up to today, and it is about 9 weeks old. I put the same medication on the water as the one I put on it's water when it was 3 weeks old, since 7 days ago. It's condition seems to improve, but the signs are still noticeable. It's brothers and sisters(there are 4 of them), eat and drink on the same feeder and water container, but they all seem healthy looking, except one when it was 4 to 5 weeks old, and last week. That one look siginficantly less sick than the other one before, and it is about 50% taller than the chick that is experiencing retarded growth. The one that look less sick, look healthy since few days ago. Those are the only signs.

I have a rooster, who is 25- 33% shorter than it's brother. It's brother started to crow when it was about 6 months old, while the significantly smaller rooster started crowing when it was 15 months old.

I checked the poop today, and I didn't see any diarrhea and blood on it's poop.

 

[Stiggy]

sometimes this happens for no reason, I had a silkie chick that just didn't grow, at 3 months old he was the size of a week old chick, same feathering as a chick. no matter what I did or fed he never grew, then he died. I'm not saying it will happen to you but it does happen. since the others arnt sick I doubt its highly contagious. Cocciodicus and sinus infections severely stunt their growth

 

[Luckybaby]

He/she died about 8 days ago. About 3 weeks ago, I started putting amprolium mixed with ethopabate in it's water 7 days consecutively since it look inactive, and it's feathers are ruffled, and some parts of it's wings are touching the ground. He look active on the fifth day of treatment, and I let him out of his cage after the 7th day of treatment. His wings are still touching the ground and it's feathers are a little bit ruffled, but it is active, for about few days after the 7th day. Four or five days before it died, it began acting sick again(inactive for a long time). Two days before it died, I let it stay in a coop with it's siblings a long with other bigger teenage chicken because the other coop are overcrowded, it complains by making noises at night if it is not with it's siblings(my neighbors might complain), and I thought that it can escape easily if the other chickens will try to peck it. However, I was wrong about escaping easily, since my mom told me that the other chicks are pecking it continuously and it didn't manage to fly out of the coop, unlike it's siblings which are already out of it, when she went inside their cage. I didn't see any blood caused by pecking, but it seems that it is significantly physically hurt. I really want it to live, despite, it being significantly smaller (about 66% smaller) than it's siblings.

 

[Stiggy]

Sorry to hear about that, sometimes these things just happen.