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“Wing Rap” by Dr.Teresa Morishita Question: I noticed that some of my laying hens occasionally lay eggs with double yolks. Will this be a problem for my flock? How is it formed? Answer: Before we answer this question, let’s take a look at how an egg is produced. Looking at the photo, we begin at the ovary. The ovary is a cluster of various sizes of developing eggs (yolks). Normally, a yolk is released and enters a thin-walled infundibulum, the first part of the reproductive tract (oviduct). It is in the infundibulum where the egg can become fertilized if sperm are present. The egg then passes to the magnum where egg white is placed around the yolk. The egg then passes to the isthmus where the shell membranes are placed around the egg. The egg then moves to the shell gland (uterus) where a hard calcified shell is placed around the developing egg. The egg  temporarily passes through the vagina before it is laid. A double yolk egg is produced when two yolks are released rather than one. The production of double yolk eggs appears to be due to genetic factors. There should be no disease problems associated with the production of double yolk eggs. Teresa Y. Morishita, DVM, PhD, Dipl. ACPV is a Professor and Extension Poultry Veterinarian in the Department of Veterinary Preventive Medicine. She is a board-certified poultry veterinarian and is also the Director of the Avian Disease Investigation Laboratory at The Ohio State University. She welcomes your questions and invites you to contact her at the Department of Veterinary Preventive Medicine, The Ohio State University, 1920 Coffey Road, Columbus, OH 43210 or contact her through this website at www.oardc.ohio-state.edu/poultry/