Usually it costs less for backyard birds than commercial layers. Infectious bronchitis, a respiratory virus, common in chickens can cause reproductive and egg shell disorders. I lost quite a few hens who had survived it when they were young. Wrinkled egg shells or other abnormal shells can be common in hens with IB virus. Sneezing every few minutes for several weeks was the common sign I saw. But reproductive problems are also common after age 2, especially in high production birds.