How old are your birds (sorry if I over read that part). Mine go into a little bit of a funk if the weather changes quickly. They go back to normal after a while. I just feed them regular 16% layer feed and some leftover. They get their grit and oyster shell and that is where it ends with me. I do treat with Apple cidar vinegar and yoghurt on occasion and I deworm and treat for pests. I am trying to make money on my birds so I am very stringend on output and how much money I spend, since I am trying to live on a tight budget. I used a heat lamp last year when temps went into a minues but that was about it. I will try and go completely without it this year. I replace my layers every 18-20 months at which time they still lay well and I get good money for them. I incubate like crazy and process all excess roos. If your girls are laying age and not laying, maybe they don't like their surroundings? Maybe something stresses them?