In some cases, these eggs can be seen to be very close together in the oviduct. These developing eggs may reside together in the shell gland. The areas where the two eggs are touching will not be properly calcified and neither egg will have adequate shell quality to support an embryo to hatching due to excessive moisture loss. Sometimes the two eggs can be separated by a greater distance in the oviduct. Sometimes that does not happen, and two eggs will be seen in the tract.
Overweight hens can also develop some severe reproductive problems that can be fatal.
In some cases, it appear that oviduct motility is impaired and the oviduct becomes impacted with developing eggs. Internal ovulation takes place when the follicles are not picked up by the oviduct, but instead fall into the body cavity. Internal laying is seen when the eggs are picked up and descend the oviduct, but for some reason, they back up and exit into the body cavity through the oviductal opening at the infundibulum near the ovary. Typically, hens that do this once, usually do it quite often. One University of Alberta broiler breeder hen that has been photographed here was excessively heavy and had a peculiar penguin-like gait.