I introduced a 2 day old Speckled Sussex to my 10 day old Barred Rock and Americauna. I noticed the new one was a bit unstable on her feet. Seemed to kinda tip over while standing or lose her balance when scratching or shaking her head. I saw her drink water and peck at the food. The older ones pecked at her abbot but i shooed them away and distracted them with some fresh dirt to dig into. Today, my husband saw the little one running after the two larger ones in a game of keep away, most likely. When I got home, all three were sleeping. I grabbed the little one to see if she wanted to sleep in my hand for awhile (it calmed her down when I first got her). I was surprised to see that she was already sleeping by the time I got to the couch. She stayed in my hand for about an hour. I noticed she had a little dried poop on her butt, I removed it with a warm cloth. I put her back in the cage and she just laid there unresponsive. Over the next 20 minutes, I dipped her beak in the water, and that would at least make her move her head. Then she started to, what looked like, gasp for air and jerk her head. She did this for 10 minutes or so. I tried a little sugar water but she couldn't drink it. I rubbed her head, she finally stop gasping, opened her eyes, and passed away. Cry fest. This is my first time owning chickens. Does this just happen? Could I have done something to prevent this? Do i need to completely clean out the brooder and throw away the food and water in case it's contagious? Sad night.