Can chickens develop a vitamin deficiency if they eat commercial feed, which is supposed to meet all their nutritional needs? My pullets are 24 weeks old (not laying yet). They eat DuMor grower/finisher crumbles. They don't free range, but when available I give them grass clippings or shrub trimmings to pick at. They also eat the occasional treat of mealworms, some scratch and kitchen scraps (produce only, no bread or other human food). Their favorite treat, which I try to make as often as I can, is their regular crumble mixed with water to form a mash. So the vast majority of what they eat is their crumble. Can they still get a deficiency with this kind of diet? I'm asking because one of my pullets has started throwing her head back and "star-gazing", and my searches on BYC and Google lead me to believe it might be wry neck, though I don't know why, and why at this age (supposedly it's usually a young chick problem). It's very infrequent and not severe (yet) - for example, the other day I sat with them for about an hour, and she did it only 2-3 times, briefly, like in the video below. I read that it's caused by a vitamin E deficiency, or a head/neck injury, or genetics. She's a bit old to be showing this for the first time now if it was genetics; she has no injuries; so I'm left with the vitamin E deficiency, and wondering how that could've happened given her diet...? Should I adjust anything in how/what I feed my chickens? Is DuMor not a good brand? Should I cut out the occasional treats? (they're really no more than a spoonful per chicken every couple of days). What should I do about this pullet now? I took away their food and water last night and waited until about 9am this morning, to get them hungry and thirsty, and then gave them a smaller container of water with NutriDrench in it, and their favorite crumble mash, also with NutriDrench in it, to make sure they all get a good dose. It's all they're gonna have for food and water until they've finished the mash, to make sure they each get some in their bodies. Any advice would be appreciated!