Chickens usually go into their 1st molt around 1 year old....some a little sooner, some much later. Even then it might not be a full blown molt, it could be a mini molt....for example; a chicken might lose just tail feathers and that's all. Molts usually occur during the fall, but my experience has been that it can occur anytime. They mostly start losing feathers around the back of their head/neck areas working its way down its back, wings, undersides and tail. Full blown molts last for several months or longer, egg production slows to almost nothing and in most cases it stops altogether. My 4 Barred Rocks are 2 years old and only one of them went into a full blown molt this past winter. We had record cold temps for 2 weeks straight in January and I had to bring her in the garage and keep her in a cage with plenty of hay in it to keep her warm. She looked pathetic too. I fed her plain yogurt to keep her immune system built up and boiled eggs (extra protein) mixed in her feed to make a mash. The other hens picked on her too, so seperation was imperative. The rest of my Barred Rocks have never had any kind of molt whatsoever. I wouldnt say they are cranky, more like stressful for them....because their systems are all messed up and everything just about shuts down to concentrate growing new feathers. Also, getting picked on adds to the stressfulness. This is another reason why I give them probiotics while in molt. Whenever I see my chickens losing feathers, I first carefully inspect for lice/mites, then if it's all clear...I know it's a molt. I hope this helps.
