Can a Change in Feed Mess with Egg Production?

Hi all! About two weeks ago, I switched my girls from 16% layer crumbles to 18% all flock pellets. I feed oyster shell for calcium. They free range through the small backyard. I have 5 layers and 2 pullets who should be laying by end of next month. I was getting 4 or 5 eggs a day pretty regularly, but since I changed feed, production is waaay down. I have one BO who has quit laying all together. There are several other things it could be but the drop off in laying started right about the time I changed the feed. I thought I was doing them a favor, but now, who knows!

The other things I have considered:

1. Broody Hen - Since then, one of my cochins has gone broody for the first time. She is sitting on purchased fertile eggs in one of our two nests. I thought maybe the reduction in nests was freaking them out so I added a new one (for a total of 3, one occupied by a broody). The next day, no one laid. Since then, a few have laid here and there, but nothing better than before.

2. Mites - I have looked and looked and checked and don't see any evidence of mites/lice. I will research futher what to look for exactly, but they look clean, bug-free, and healthy.

3. Weather - It has been pretty rainy here in Iowa but not hot at all. In fact, it's been beautiful.

4. Molting - I see really no evidence of them molting. Again, I will research what to look for, but I don't think this is the case. Shouldn't they have done that earlier this year? I don't believe I have ever seen them molt, and I've had them a year now.

5. Age - I have one 2-year old hen, 4 that were 1 in April, and two that were hatched in February of this year, so age is not a problem.

6. Incidentals: My BO that has stopped laying altogether is blind in one eye. It started last winter when she got pecked in the comb and eye (I think.) Since then, her eye has been cloudy, with an indistinct pupil. Right before this egg kerfluffle, her eye degenerated quickly to completely obscured (looks like a cataract.) Her other one is fine and so is everyone else's so I don't think it's occular Mareks.

7. Hiding/Stolen Eggs - I have checked and checked the backyard and found no sign that anyone is laying anywhere but their nests. It's pretty wide open. We are in the city, and they are fenced, and the kids and I watch them off and on all day, so if something is eating the eggs, it'd have to be really, really sneaky. I have seen no sign of eaten eggs either.

I am just stymied and frustrated about this whole deal. I want to fix whatever is wrong, but I don't want to stress them out with any other changes unless I KNOW what's wrong.

Ideas? Advice?

Thanks,
Angela