Oh, cppeace, chicks and bunnies...that is a GREAT picture!
I assume the herbs would be mint, oregano, garlic, etc. You might check the fresh eggs daily (FED) blog as the lady that manages or publishes it, whatever the correct term is, is a big proponent of herbs as preventatives. I may be mistaken but I was think she starts very early like day 1 with some herbs.
After reading her blog and book we decided to start on the brewers yeast / garlic powder and probiotics powder from day 1 mixed with the food. We just added some fresh mint on their 3 week birthday and they loved it. Of course keep in mind with the fresh herbs you will need to provide some sort of grit. I believe the FED talks about grass clumps with the soil attached but we went with commercial chic grit.
Good luck!