I am assuming there are no physical problems, infestations, disease, etc. since you didn't say so. Barring any other problems, if you have them over fresh grassy areas every couple of days, they should be getting protein from bugs, worms, etc.
If they were laying alright before, the problem might be the shorter days and have nothing to do with protein. Chickens will reduce laying with shorter days (and, colder weather). They need about 14 hours of sunlight to lay at the rate they do during the summer. My 12 hens have gone from about 11-12 eggs per day to 4-5 eggs per day in just the past few weeks. You can keep their egg production up by keeping a light in the coop and setting it to come on early and stay on until late...so they get their 14 hours. It's thought nature built this into them before they were domesticated. When they were on their own, the winters came and food was in short supply, they needed the nutrition to survive the winter, so egg production was greatly decreased. With the care they get today, artificially creating "day light" is generally accepted not to do them any harm as long as they are receiving proper nutrition.