Have a look at this article.
POULTRY INTERNATIONAL DIGITAL EDITION DECEMBER 2013.
I have for many years fed vitamin C to my birds through the addition of fruit, lots of it, to their diet.
I have also found Vitamin C to be a good remedy for leg problems. If a bird is battling with a joint injury heavy doses of vitamin C does help.
It has always been of use as an additive for stress but the humble C is far more important than you would realise.
WHY VITAMIN C?
When a bird is under stress, either through heat or predators, vaccination or simply mishandling on the part of the poultry keeper, the first thing it will do is pant. They pant very heavily even when laying.
This panting is the way a bird will take in extra oxygen which will hopefully work like the adrenaline in our system to give it more options in case it has to run.
Unfortunately they do get more oxygen but in the process lose a lot of vitamin C and pant out a lot of their mineral content in the body as well.
This needs to be replaced. Heavy doses of vitamin C do help . In cases of heat stress you can also add a tablespoon Bicarbonate of Soda to their drinking water last thing at night. Hens that pant heavily due to heat stress also lose a lot of calcium . The egg for the next day is being manufactured at night, which is when they are at rest and the bicarb will be more effective at night.
Vitamin C is also a great reliever in cases of leg or joint problems as it rebuilds muscle and cartilage better than any other drug.
Vitamin C is used widely in animal veterinary science for dogs, cats, poultry, cattle and sheep.