Hen's laying incomplete eggs

[hayhens]

We have just bought 3 lovely hens for our backyard coop. Having chickens is very new to us and we are trying to learn as much about them as possible. We have had them now for 2 weeks. 1 is laying every second day and producing lovely brown eggs. However this morning when i went down to check the coop, there was what appeared to be an incomplete egg in her laying box (it looked like egg white and a bit of yolk but no shell?). What caused this? She is 18-20 weeks old, a very happy, friendly and hungry, energetic chicken?

One of the other hens had started laying this morning also (her 1st egg!), the egg looked perfectly brown but had a white area on the bottom side of it. Is this an issue? She laid it on the roost, so i'm not sure how it didn't crack?

They eat laying mash that we bought from the breeder who told us it has absolutely everything in it that they require to be great, healthy layers. He said it was top quality stuff.
They free range in our yard for a few hours per day, could they have eaten something in the yard thats upset them?

Any help and advice would be appreciated!

 

[scratch'n'peck]

It might be because she recently started laying and she is still adjusting. Hopefully she didn't accidentally break the egg and eat the egg shell, because you wouldn't want her to get into the habit of eating eggs. They probably have enough calcium, but it never hurts to offer oystershell free choice in a separate bowl and they will eat as much as they need.