I saw an article online http://ohioline.osu.edu/vme-fact/0023.html It says that you can draw 1 cc per 100 grams of weight. Do you think that sounds true? Also, is there a minimum age the birds should be before you draw blood?
As far as maximum amount of blood you can safely draw, that seems about right, or maybe even a bit low. But as far as an amount for diagnostic tests on a sick bird, that seems a bit high. 1cc on an adult chicken, even a sick one, isn't really much, but a good lab can do a lot with less than that. I work for a board certified avian vet, and we almost never draw more than 1/2cc of blood on birds which is typically enough for a CBC and chemistry panel. Sometimes we will draw more if we need to do blood lead or something like that. The only time I've ever seen him draw more than that has been on much larger birds, like the bald eagles, pelicans, or turkey vulture at the zoo. As for minimum age, there really isn't one, but you have to decide if the stress is worth the risk for the venipuncture as the stress of drawing blood is more dangerous than the actual amount of blood drawn even in a healthy bird. In a day old chick it probably isn't, but a chick that's a few weeks old may be better able to withstand the stress.
What do you want to draw blood for? Of course it can be done, but it depends on why you want to do it. If it's for certain tests like Avian Influenza or Salmonella Pullorum then your state probably has a minimum age. (like for show birds) If it's for NPIP they have a set of rules about ages of birds that are tested (don't have them in front of me right now, but they are in my book. I can look them up if you need them)
The N.P.I.P. people here require the birds to be at least four months old when they test for Pullorum/typhoid. WE are planning on sending blood to a lab to test for Mycoplasma. Is there a minimum age for that?