Mille Fleur D'Uccle Butt Problem?

[bhufflepuff]

I have a two month old runt rooster that was separated from his other siblings when they were about three weeks old. He was getting run over a lot, so he has been by himself since then. When we first pulled him out of the lot, he was hunkered down like he was in pain, but he has never been sore to the touch. He eats great and drinks fine too. He is a happy example of what a little roo should be. The only problem is that his tail constantly pulsates.
I'm not really sure how to explain this other than that it looks like he has shivers in his back butt area. He walks fine, is outgoing, and plays a ton, so I don't think it is affecting him to much, but I would like to know what could be the cause of this. I know my description lacks details, but I can gladly record a video of it so that you can better see the problem if need be. I am just not sure how to upload a video onto this forum. Thanks in advance.

 

[Eggcessive]

What do his droppings look like? Does he seem constipated? What do you feed him, and do you give him chick grit to help digest grass and foods other than chick feed?

 

[bhufflepuff]

Droppings look normal compared to everyone else's. Does not seem constipated at all. Grit is a yes and other than chick starter he gets grass and some bugs while grazing.

Like I said. It's been almost a month now. It doesn't seem like its a stomach issue. It seems more like a muscle issue. We think his bigger siblings might have run him over and caused some damage to his backside. He walks fine and eats and drinks, but just has this nonstop quivering.

 

[Eggcessive]

A video would be helpful. There is a place to insert the video in the reply box or give a link to YouTube. There is a disease called Avian Encephalomyelitis (AE,) which can affect chicks up to a month of age. It usually causes tremors of the body, and chicks may be found lying on their sides and lame, but he doesn't sound like it. Here is an article about it: http://www.thepoultrysite.com/diseaseinfo/9/avian-encephalomyelitis-epidemic-tremors/