Avian Sour Crop and Impacted Crop – NAVLE Study Guide

Overview and Clinical Importance

Crop stasis (also known as sour crop, slow crop, or crop impaction) is a common gastrointestinal condition affecting pet birds, poultry, and wild avian species. The crop (ingluvies) is a diverticulum of the esophagus that serves as a temporary food storage organ. When the crop fails to empty properly, food ferments and becomes a breeding ground for opportunistic pathogens, particularly Candida albicans. Understanding the distinction between sour crop (fungal/bacterial overgrowth) and impacted crop (mechanical obstruction) is essential for the NAVLE, as treatment approaches differ significantly.

This condition is a frequent cause of morbidity in hand-fed juvenile psittacines and backyard poultry, making it a high-yield topic for board examinations. The NAVLE commonly tests recognition of clinical signs, differentiation from other GI disorders, and appropriate treatment protocols.

Anatomy and Physiology of the Avian Crop

Functional Anatomy

The crop is an expansion of the esophagus located at the base of the neck, just outside the thoracic cavity. It serves as a temporary storage organ that allows birds to consume large amounts of food quickly and digest it later. The crop structure varies among species: gallinaceous birds (chickens, turkeys) have a true, well-developed crop; waterfowl (ducks, geese) have a rudimentary, narrow crop; and pigeons have a unique crop that produces crop milk during brooding.