My hens did that when it got real cold and I think went through a molt. How old are your hens, they can typically go through a molt around 9-10 months, some don't til they are 18 months. I had 30 chickens and did not get an egg for about 6 weeks. Some times it just last for about 2 weeks. I heard you can give them redpepper flakes ground to stimulate but really I'm not sure how much. I never tried that. I actually had to buy storebought eggs for a couple weeks.Yuck!!