That is very strange. In 5 years I have only had one chicken out of hundreds (yes HUNDREDS) that had a prolapse after she could not pass a triple yolk egg. I had to help it out and she prolapsed from straining.Point well taken. I was feeding layer to my layers until I got 9 week old chicks. Then I switched everyone to Flock raiser. I had oyster shell in a separate bowl but started getting soft shelled eggs and had a chicken with a serious prolapse.That was when my vet came over and told me they had a calcium deficiency and told me how she feeds. I had to give several birds injections of calcium gluconate. The prolapse has healed and everyone is laying hard shelled eggs again. I'm now mixing the flock raiser and the layer, feeding back egg shells a couple times a week and have bowl of oyster shells around as well as mixing some in the feed. I don't know how to keep their calcium levels up on just the flock raiser. The chicks are just 12 weeks old now and run with the big girls and eat their feed. I am open to any suggestions but am very worried about getting more prolapses from straining with rubber eggs. I almost lost a beautiful hen and am thankful to this vet. Most wouldn't put in the time she has with my chickens (or don't know anything about them).
I have gotten rubbery eggs when I forgot to refill the oyster shell, but besides that - no issues at all. I do not use flock raiser, as it is not an option here. My choices for chickens are: Game bird breeder, chick starter, grower/finisher, layer and other feeds for different species of birds (turkey grower, turkey starter, etc.)
Did your birds go for the oyster shell? Maybe they just were not used to it? Maybe the change where they had layer without oyster shell and switched to something new confused them?