Ya, Metronidazole (flagyl), I was told 1 tablet (250mg) once daily, but my hen is a large bantam size. Idk what size chicken you have and if it makes a difference. I was also told to swab iodine (poividone/betadine..same stuff) on the plaque. 5-10 days, also change the water as often as you can. Now, I read a whole detailed article earlier in the day about trichomonas and it mentioned how an acidic environment is not preffered by the organism. This made me wonder about apple cidar vinegar in the water and if that has a desirable effect here. I have galvenized waterers and cannot use the ACV, but I have bought a solution reccomended by the doctor that diagnosed my hen's condition. It's called Oxine, you can put it in the water to keep the bug from surviving in the water and infecting other birds.
I am worried that the rest of the flock will get it since she was not separated until after I noticed she was sick, which could have been a week or so before it was apparent. I also wonder where it originated, do I have a carrier bird in the flock or did an infected wild bird come drink out of my water...one will never know.
Here is the link to the article, but I will warn that it may require some knowledge in veterinary science as it uses some terms that may not be familiar to all.
http://www.albertaclassic.net/trichomonas/trichomonas.php
Edit:
I had never tube fed a chicken until this past monday. It is fairly easy, although I was super nervous. I do have some veterinary experience, but none with chickens. I was lucky enough to run into a lady who showed me how to do it, after I had tried it on my own 1st. I was so nervous about getting it in the wind pipe, but it seems that it is difficult to do that. I figured the hen would die anyway so if I killed her (it would suck) but it was a last ditch effort. I have been succesful so far (4 days in) and she is looking better, but I think it will be some time before the plaque goes away. I plan to make a video of me tube feeding her this weekend so that others may see what it looks like. A lot of stuff says to be sure to visualize the glottis (which is the opening to the wind pipe) but I cannot see it. I think the plaque is blocking it from my view. I pray every time I force feed her that I will not go down the wrong tube. Today, she seemed to cough a little when I put it in, so I took it out and back in and she swallowed so I knew I was in the right one then.