The crop is a muscular bag at the bottom of a hen’s neck which stores feed for the day.
Normal crop function
First thing in the morning the crop should be empty, and will gradually increase in size as the hen eats. In a healthy hen the crop will be roughly the size of a small tangerine when full; the feed will pass out of the crop into the gizzard overnight where it will mix with grit and be ground down before the cycle starts again.
Pendulous, or spastic crop as it is often known, occurs when the crop muscle becomes stretched and the crop will fill to a massive size (Figure 1). Hens usually cope with this condition fairly well, but it can in some cases lead to sour crop. The crop may never return to normal due to the muscle layers being overstretched and damaged.