Updating this post as continuing to have hen eating problems! Below is what I originally posted - very helpful to know that definitely likely to be about moulting. I've tried feeding mash, with a little success but less as time has gone on. They will devour cold pasta or rice and are foraging fairly enthusiastically when I am able to let them out into the kitchen garden.
However I think one of them is crop bound.Her crop seems very big and firm all the time, even when first out of bed in the morning. I read about giving olive oil to soften the stuff in the crop and then massaging it. I have tried that - though no idea how much olive oil to give and how to get hen to open beak so I can pour in oil! And how long do I massage for? She is very thin but seems a bit less lethargic than she was - I think. But the actual crop continues the same. I think that some of them are doing rather more solid poo than before.
"One, perhaps two of my hens are excreting what looks almost like water. I've not had my eye on the ball because of family problems and I think it has probably been going on at least for a week. Before that I had noticed poo that was quite runny.
They are moulting at the moment so look a bit miserable anyway. Pottering about fairly normally but I think a bit subdued and eating much less than normal and less interested in food."