Oops, Sorry, it wasn't in a book, but the 2007 September issue of Practical Poultry. Page 43, in an article about molting called All Change, written by Bob Cross.
"Lastly, although rare, poultry have been known to change sex. When this happens it's usually as a result of the reproductive organs having been destroyed by disease. The change becomes more evident after the moult, when the new feathers develop to present the bird in it's re-gendered form.
Professor Crewe, at Edinburgh University, observed a productive buff Orpington hen that, at three and a half years old, took on the appearance of a male, and sired chicks the following year. A similar case was reported by Armsdorf in 1947, and concerned a New Hampshire Red hen which changed in the same way. On both occasions post-mortem examination revealed the ovary had been destroyed and an oviduct damaged by disease, these being replaced by testes and vas deferens which proved functional."