I swear by Neem seed oil. Keeps my kids lice free and my dogs flea free. I googled to see if it can be used on chickens and it brought me to this thread. I hope you don't mind me putting my 20c worth in to the discussion.
I believe I've read somewhere that Neem, once mixed, doesn't have a particularly good shelf life and will lose its effectiveness quickly (Please don't take my word for this though, I'm sure the information is out there if you'd like to check for yourself).
To use it on my kids and my dogs (and their bedding) I use it in a preventative manner. It works a treat. I take about a tsp of 100% Neem seed oil and mix it with the same amount of liquid soap (shampoo for the kids, flea control shampoo for the dogs) so that it will disperse in water. If you don't mix it with the soap of some kind, it will just float on top of the water and not mix. I then put it in to a spray bottle (roughly a cup in volume I guess) and fill it with water. Shake it to mix and spray away.
I find I don't need to get it on their skin, although I am certain some would find its way to their skin. I do however rub my dogs once I've sprayed them to spread it over their coat. The kids get a spray at the base of their hairline at the back, a spray above each ear and one in the middle/top of their head. Went from having regular occurrences of nits/fleas to NONE EVER once I started spraying the kids each morning before school. The dogs and their bedding just get sprayed when they are bathed (I also mix some Neem in to the dog shampoo I use and leave the lather on for a few minutes before rinsing).
I would probably use it on my chickens now that I've read this thread. Perhaps oiling the roosts/coop/nesting boxes and then a drop under their wings and back of their neck to start the preventative ball rolling and then the watered down spray, directly on to the chickens to maintain.
Trust me, you don't need much at all - I think that even a mix of 10% Neem to 90% of a cheaper oil might even do the trick. It's pretty good stuff!! A lesser mix might also suit those that still have concerns over it's toxicity. It does stink, but I find with the spray on my kids and dogs hair that the smell goes away as it dries and you would have to put your nose directly on the sprayed area to smell it. Either that or I just become accustomed to the smell after the initial heavy waft of garlicy scent when I first spray haha.
Thank you for contributing this very good info from your firsthand experience!
