Updated: September 23, 2014
The crop is a pouch-like enlargement of a bird's esophagus. It is located at the base of the neck, between the jaw and the breast muscle. The crop functions to store and moisten food, and can hold a large volume. Food from the crop is gradually passed into the stomach throughout the day. The crop also stores food to be regurgitated to feed baby birds or the bird's mate, during nesting. Crop stasis is a condition in which the crop fails to empty at a normal rate.
Normally, ingested food moves from the crop through the thoracic esophagus, to the first stomach, called the proventriculus. From there, it moves to the second stomach, the ventriculus, then through the intestines. Movement of food through the entire gastrointestinal tract is controlled by highly coordinated waves of contractions, called peristalsis. Disruption of peristalsis prevents food from moving through the intestinal tract, causing food to back up into the crop. Crop stasis is similar to a clogged drain, where the sink fills up with water. Just as the problem is not the sink, but the drain, most cases of crop stasis is caused by disease in the lower intestinal tract, not the crop itself.
Obstruction of the intestinal tract at any point can also prevent food from moving. If the bird continues to eat (or is force fed) in the face of gastrointestinal tract obstruction or disruption of peristalsis, food will eventually back up into the crop.
There are many causes of crop stasis. A few of the most common include:
Obstruction – ingested foreign objects or neoplasia (tumors)
Viral diseases –especially Avian Bornavirus (Proventricular Dilatation Disease) and, in young birds, Polyomavirus
Bacterial infection – occurring anywhere in the intestinal tract
Fungal infection – in the crop or proventriculus
Metabolic diseases – liver disease, pancreatitis
Toxins – especially heavy metals such as lead or zinc
Improper feeding formula – in young, unweaned birds
Baby birds that are being hand-fed a feeding formula may develop crop stasis due to improper temperature of the formula (too hot or too cold), improper consistency of the formula (too thick or thin), or environmental problems, such as a cold temperature or low humidity.
What to Watch For
Vomiting, regurgitation or diarrhea
Overdistension of the crop
Undigested food in the droppings, or a foul odor to the droppings
Listlessness or lethargy – excessive sleepiness, ruffled feathers, tucking the head under the wing. These symptoms warrant an immediate visit to the veterinarian. Birds that are too weak to stay on a perch are in critical condition.
Decreased appetite in adult birds
Lack of a feeding response (bobbing or begging) in baby birds
The veterinarian will recommend specific diagnostic tests depending on several factors, like the duration of crop stasis, whether the crop is emptying slowly or not emptying at all, the age of the bird and other symptoms that are present. To find the cause of crop stasis in adult birds extensive diagnostic testing is usually required.
A complete history is extremely helpful in reaching a diagnosis. Be prepared to tell your veterinarian when you first noticed a slow-down in crop emptying, the type and consistency of feeding formula, and if other symptoms are present. Additionally describe your bird's chewing habits and note any potential exposure to other birds.
Diagnostic testing your veterinarian may perform include:
A thorough physical examination
Sampling the crop and/or feces for bacterial culture and cytology (looking at cell types for evidence of infection or inflammation)
A complete blood count (CBC) and serum biochemistry panel
Radiography (X-Rays) to look evidence of intestinal disease, size and density of the liver, kidneys or other organs. Often a Barium contrast study is needed to detect slowing of intestinal motility or the presence of foreign material and tumors.
Infectious disease testing – especially for Avian Bornaviruses, Polyomavirus and Chlamydia
A surgical biopsy of the crop may be needed to diagnose Bornavirus
Endoscopy – viewing the intestinal tract an endoscope to collect samples for biopsy or culture
Treatment for crop stasis may include any combination of:
Hospitalization for intravenous or subcutaneous (under the skin) fluids and injectable medications for critically ill or dehydrated birds
Antibiotics or antifungal medications
Anti-inflammatory medications, such as celecoxib or other non-steriodal anti-inflammatory drugs, if bornavirus is confirmed or suspected.
Medications to protect the intestinal tract , such as antacids, or medications alter the motility of the intestinal tract such as metoclopramide.
Surgery or endoscopy to relieve intestinal obstructions
If the gastrointestinal tract is functioning properly, the crop of a normal adult bird should empty at a regular rate. Generally, the crop remains relatively small and not noticeable by most bird owners. If you notice a swelling on the neck just before the entrance to the thorax, and the swelling does not decrease in size or disappear after a few hours, consult your veterinarian.
The crop in neonatal or baby birds is much more noticeable, since it is larger than an adult's crop and it does not have the same covering of feathers. The crop should empty at a steady pace following feeding. If the crop is not emptying at a normal rate, make sure the temperature and consistency of the food is correct, and that the bird is housed at the proper environmental temperature and humidity. If the crop is not emptying properly following theses measures, seek veterinary attention.
After seeing your veterinarian, be sure to:
Give all medication as directed, for as long as directed, even after the symptoms appear to be gone.
Watch for a change in the droppings, or the development of vomiting, regurgitation and report any changes to your veterinarian.
If improvement is not seen, report this to your veterinarian.
Crop stasis refers to a condition where the crop, which is a diverticulum of the esophagus, stops emptying and becomes distended with fermenting food and fluids. This is a serious, life-threatening condition and needs to be treated by a veterinarian immediately.
Normal Digestive Process
The upper gastrointestinal of pet birds has several unique features and when food is ingested, it goes through the following process:
After being swallowed, food moves into the crop. The function of the crop is to moisten, soften and store food.
Food then moves from the crop into the first stomach, called the proventriculus. The proventriculus contains glands that secrete enzymes and acid to begin the chemical digestion of the ingested food.
Once these digestive chemicals have been added, the food then moves into the second stomach, the ventriculus. The ventriculus contains two opposing sets of muscles, which grind and macerate the food. Food typically moves back and forth between the proventriculus and ventriculus several times before moving on into the intestines.
Movement of food from the crop to the proventriculus to the ventriculus is dependent on highly coordinated contractions (peristalsis). If the proventriculus is empty, food will move immediately into the proventriculus without being retained in the crop. If food is present in the proventriculus, it will be stored in the crop.
In birds with normal gastrointestinal tract motility, peristaltic waves can be observed moving across the surface of the crop. These waves are easy to see in baby birds, since the crop lacks a covering of feathers. When the crop is filled with food, 1-3 peristaltic waves should move across the crop per minute. In normal birds, peristaltic waves are coordinated throughout the entire gastrointestinal tract, and the waves observable in the crop reflect movement of the gastrointestinal tract as a whole. Any disease process that inhibits peristalsis or disrupts its coordination will cause crop stasis.
Many diseases, both within the intestinal tract and in other organ systems, disrupt or inhibit peristalsis. Additionally, any physical obstruction occurring along any point within the gastrointestinal tract will cause food to back up into the crop. There is a tendency to think of crop stasis as a problem with the crop itself. Although disease within or surrounding the crop can cause crop stasis, the disorder more often lies in the lower intestinal tract or disease in other systems. It may help to think of the crop as a kitchen sink. When the kitchen sick backs up, the problem is in the plumbing, not in the sink itself.
There are many causes of crop stasis in birds. Crop stasis can be caused by diseases of the digestive tract or can occur as the result of toxicities, disease of the nervous system or metabolic diseases. Many contagious diseases cause crop stasis, so it is important to inform your veterinarian of any potential contact – direct or indirect – with other birds. Possible causes of crop stasis in birds include:
Viral infection. Several different avian viruses may cause crop stasis. Proventricular Dilatation Disease is caused by a virus (Avian Bornavirus) that attacks the nerves that coordinate peristalsis in the intestinal tract. When this nerve supply is disrupted, the coordination of movement from the proventriculus to the ventriculus is interrupted. Initially food that is passed appears undigested in the droppings. Later in the course of the disease, movement of food through the intestinal tract slows or stops completely, causing food to back up into the crop. Other viruses, such as polyoma virus and herpes virus may cause ileus (gastrointestinal tract stasis). With these viruses, however, crop stasis will usually be only one of several symptoms. Viruses can be transmitted by direct exposure to another bird, shared food or water dishes, or on your hands or clothing, depending on the type of virus.
Obstruction. Ingested foreign objects may block the intestinal tract. Psittacine birds (parakeets, cockateils and parrot like birds) have powerful beaks and a strong instinct to chew. Objects that commonly obstruct the intestinal tract include string toys, bark or wood shavings, and pieces of rubber toys. Birds that are provided grit as a dietary supplement will occasionally overeat the grit, resulting in gastrointestinal tract obstruction.
Growths. Neoplasia (cancer) or papillomas (wart-like structures) may occur anywhere along the gastrointestinal tract.
Toxins. Heavy metal toxicity, caused by ingestion of objects containing lead or zinc, is one of the most common diseases seen in pet birds. These toxins affect the nerves that supply the gastrointestinal tract and coordinate peristalsis. Not all birds with heavy metal toxicosis have crop stasis, and most have other symptoms, especially neurologic signs.
Bacterial infection. Bacterial infections may come from other birds, from an overgrowth of dangerous bacteria on dirty food or water bowls, or spoiled foods. Often, small amounts of potentially dangerous bacteria will live in the intestinal tract without causing harm. This population of bacteria can overgrow and cause disease if the bird's immune system is not functioning properly, as may occur during times of stress. An overgrowth of harmful bacteria may also occur when antibiotics are used improperly.
Yeast infection. Candida is a type of yeast that normally lives in small quantities in the intestinal tract. Stress or antibiotic use can also cause an overgrowth of Candida. These yeast commonly invade the wall of the crop itself, and can also invade the lower intestinal tract. Yeast infections are a common cause of crop stasis in baby birds.
Parasites. If large numbers of intestinal parasites such as roundworms and tapeworms infest the intestinal tract, complete obstruction may occur. Trichomonas may occasionally cause crop stasis in small psittacine birds, especially budgerigars.
Metabolic disorders. Liver disease, diabetes mellitus, renal disease
Dehydration. When birds become dehydrated, fluid may be pulled from the contents of the intestinal tract, resulting in obstruction from thickened, dry food.
Goiter. Enlargement of the thyroid gland commonly occurs in budgerigars with iodine deficiencies. Birds on diets consisting only or solely of seeds are especially prone to goiter. The thyroid glands are located beside the crop and can sometimes become so large as to obstruct outflow from the crop.
Improper feeding formula in neonatal birds. Crop stasis is a common problem in neonatal birds being hand-fed. Dietary formulas that are fed too hot or too cold, or are mixed to an improper consistency can cause crop stasis.
Improper environmental temperature or humidity. Neonatal birds that are chilled or overheated often develop crop stasis. If the ambient humidity is too low, baby birds may dehydrate.
A thorough history is extremely important in the diagnosis of crop stasis. Be prepared to tell your veterinarian:
For baby birds, the temperature and consistency of the hand rearing formula, environmental temperature and humidity. Are any other chicks affected? Does the bird ingest bedding material?
Has the diet changed? Are fresh foods, such as fruits and vegetables fed regularly?
Is the bird still eating a normal amount of food?
What are the birds chewing habits? Is there access to metal objects or plants? Does the bird chew apart wood, rubber or string toys?
Are any other symptoms, such as lethargy, vomiting, regurgitation or diarrhea present?
Has the bird been exposed to other birds?
How often are the cage, food and water dishes cleaned, and how are they cleaned?
Your veterinarian will recommend specific diagnostic tests depending on the duration of crop stasis, whether the crop is emptying slowly or not emptying at all, the age of the bird and if other symptoms are present. To find the cause of crop stasis in adult birds extensive diagnostic testing is usually required. Any combination of the following may be recommended:
Culture and cytology. Sampling the crop, feces or cloaca for bacterial culture and cytology (looking at cell types for evidence of infection or inflammation).
Parasite exam. Sampling of the crop or feces to look for intestinal parasites.
A complete blood count (CBC). The number of circulating white blood cells may be helpful in distinguishing between infectious and non-infectious causes of crop stasis. The number of red blood cells may be diminished if bleeding in the intestinal tract is present.
Serum biochemistry panel. This test is needed to look for evidence of metabolic problems, such as diseases of the liver, kidney or pancreas.
Blood tests or other samples to test for for infectious diseases such as polyomavirus, chlamydiosis (psittacosis) or Avian Bornavirus.
Blood testing for heavy metals, such as lead or zinc in circulation.
Radiography (X-Rays) to look evidence of intestinal disease, foreign bodies, and the size and density of the liver, kidneys or other organs.
Contrast radiographs, such a barium studies, to look for tumors or foreign bodies, ulcerations or thickening of the lining of the intestinal tract. This test will also determine how quickly ingested material is moved through the intestinal tract.
Fluoroscopy (Performed by a specialist). This is a video or moving X ray that is used to determine if the coordination of peristaltic waves is normal. It is useful in the diagnosis of toxicity (lead or zinc), foreign bodies or viral diseases (Proventricular Dilatation D isease).
Abdominal ultrasound. This test is possible only in birds with enlargement of the liver or fluid in the abdomen. It allows visualization of the intestinal tract for evidence intestinal wall thickening, gastrointestinal masses, and foreign bodies. A specialist usually performs this test.
Endoscopy. This test allows your veterinarian to view the intestinal tract or body cavity directly with an endoscope to collect samples for biopsy or culture. Some foreign bodies may be removed with an endoscope. A specialist usually performs this test.
Crop biopsy. If Proventricular Dilatation Disease (Avian Bornavirus) is suspected, characteristic lesions are sometimes found on biopsy specimens from the crop. At this time, the only way of definitively diagnosing Proventricular Dilatation Disease is through the observation of characteristic lesions on biopsy specimens from the gastrointestinal tract or nervous system.
Exploratory laparotomy. Occasionally, surgery must be performed to observe and obtain segments of the intestinal tract for biopsy in order to determine the cause of crop stasis.
Your veterinarian may recommend one or more of the diagnostic tests described above. In the meantime, treatment of the symptoms might be needed, especially if the problem is severe. The following treatments may be applicable to some, but not all birds with crop stasis. Therapy is not a substitute for definite treatment of the underlying disease responsible for your bird's condition.
Birds with complete crop stasis and other symptoms such as lethargy and anorexia usually require hospitalization and 24-hour care.
Fluid therapy. Birds with crop stasis are moderately to severely dehydrated and require fluids. Fluids may be given by an intravenous catheter, an interosseous catheter (into the bone marrow) or subcutaneously (under the skin). The route of administration will depend on how severe the level of dehydration is.
Food that has been stagnant in the crop usually must be removed. The veterinarian may pass a small tube into the crop to empty the contents. If foreign objects or large amount of thickened, dry food is present in the crop, surgical removal of the contents may be necessary.
Fluids. Once the contents of the crop are removed, balanced fluid solutions are fed until gastrointestinal tract motility returns.
Nutrition therapy. Food is usually withheld until the crop begins to empty. However, birds have a high metabolic rate and require a constant source of energy. If food is not moving through the intestinal tract, the intestinal tract may need to be completely bypassed by administering parenteral nutrition (intravenous feeding). If only the crop is damaged, the crop may be bypassed by surgical placement of a tube into the proventriculus for feeding.
Dietary change. When intestinal tract motility returns, diet that is easy to digest may be offered. If the bird is not eating, your veterinarian may feed a liquid diet via a tube passed into the crop.
Antibiotics. Antibiotics or antifungal medications may be needed to treat or prevent an overgrowth of bacteria or yeast.
Non-steroidal anti-inflammatory medications (NSAIDs) such as celecoxib (Celebrex®) are useful in treating Avian Bornavirus (Proventricular Dilitation Disease), by reducing virus-induced inflammation in the nerves.
Intestinal protectants such as sucralfate (Carafate®)
Intestinal motility modifiers, such as metoclopramide (Reglan) or cisapride (Propulsid) may help to increase peristalsis. These drugs are administered after a foreign body has been ruled out.
Baby birds with prolonged crop stasis sometimes have an over-stretched crop. Bandaging of the crop will sometimes support the crop and aid in emptying.