IamSamSam
Songster
Selenium is not something I would recommend , it's too easy to overdose and selenium toxicity usually leads to massive organ damage. Wryneck is a shortfall in thiamine B1 and vitamin E is said to help with absorption I'm not sure what function the selenium has in this treatment.
http://www.thepoultrysite.com/publications/6/diseases-of-poultry/227/acute-selenium-intoxication/
I was told to use it for only three days strictly no longer from memory it was something about muscles and the need. But I'll discontinue if it's not required