From the name “sour crop” you can deduce the anatomical location (aka the crop) and the smell (aka sour).
What and where is the crop?
The crop is a pouch (see Figure 1) just “south” of the esophagus, used for softening feed and temporary food storage in prey species (predator avian species typically do not have a crop) of birds including chickens. The purpose of the crop is to allow a bird to quickly swallow what food it can, store it in the crop, then fly to safety and digest the meal.
Food enters the crop after exiting the esophagus (Figure 1). The crop is a stretchy pouch that lies close to the skin in the neck region and after it fills up with food, the enlarged crop can be felt. Sometimes, people feel that “swelling” and worry there is something wrong. Typically, over the next couple of hours as the food moves out of the crop and towards the proventriculus (i.e. stomach) the crop will return to its normal size.
What is sour crop?
If you’re never had the displeasure of smelling the chicken ailment “sour crop” you (and your chickens) are better off. The smell comes from a fungus called Candidia albicans which is commonly found in the environment. Following exposure, the fungus infects the cells that line the crop and causes inflammation (Figure 2). Once inflamed, food can get stuck in the crop which results in the characteristic “sour” smell. In severe cases, because the food can’t be emptied into the stomach for digestion the chicken becomes anorexic and lethargic from not getting the nutrients it needs. Like many poultry diseases, treatment is often unsatisfactory. Therefore, prevention including proper husbandry are essential toward protecting your birds from a Candidia albicans infection.
How can chickens get exposed to Candidia?
Chickens can be exposed to a high concentration of Candidia including Candidia albicans by eating rotten/moldy food, or ingesting food and water contaminated with feces. Thankfully, candidiasis cannot be spread bird-to-bird, they only become sick after a high load of exposure to Candida.
What are some signs of infection?
If your chicken has sour crop you may notice some signs of illness such a depressed demeanor, sunken eyes, decreased appetite, and regurgitation. If you notice a distended crop area that is not emptying as usual and feels doughy, this is a strong sign of sour crop. Be on the “lookout” for a foul smell coming from the mouth of your chicken, which is a sign of severe disease. If necessary your veterinarian can also diagnose an infection by culturing the fungal organism from a swab of the crop, or by performing a microscopic examination of the crop tissue post-mortem.
Like most poultry diseases, there is no specific treatment for sour crop; prevention is best! In order to prevent sour crop, it is essential to keep a clean and mold-free environment for your chickens to minimize their exposure to the fungus. This means minimizing exposure to the fungus by keeping their food, water, and litter fresh and free of contamination. A balanced diet can help prevent infection as well. If you feed your flock a commercially available diet, your birds’ nutritional needs should be met. However, if your birds are not getting a balanced diet (if you are giving to much scratch or other scraps) a vitamin A deficiency in particular could pre-dispose your birds to sour crop.
What is the treatment for sour crop?
If you suspect your chicken has sour crop, do not induce vomiting. The regurgitated material can have the yeast in it, and by inducing vomiting the material coming up may get inhaled by your chicken thereby worsening the disease, or causing them to choke. Your veterinarian can use local anesthetic to drain and wash out the crop and prescribe antifungal medications to help kill the fungus. Antifungal medications can include Nystatin in the feed, or a ketoconazole prescription. It is important to know that there is a “clearance time” required for medications in order to prevent residues in egg or meat. Because Candidia is not a bacteria, treatment with an antibiotic will enhance the disease and could wipe out the good bacteria in the digestive tract. This is one of the reasons it is highly desirable to diagnose the causative agent as opposed to “just trying an antibiotic.”
Unfortunately, once a chicken has been infected, the infection can reoccur. Finally, while I am typically skeptical of the efficacy of apple cider vinegar and there is no scientific literature to support the following, adding vinegar to drinking water to acidify the intestinal contents can potentially make the gut environment less favorable for fungal growth and may help prevent reinfections. Regardless, focus on prevention as prevention is both less expensive and results in better outcomes than treating infected chickens.