Sour crop is a yeast infection in a chicken’s crop, the expandable pouch at the base of the neck where food is stored before digestion. The infection is caused by an overgrowth of Candida albicans, a fungus that normally lives in small numbers in the upper digestive tract without causing problems. When something disrupts the balance of microorganisms in the crop, Candida multiplies rapidly, fermenting food and producing a distinctive sour smell.
How a Healthy Crop Turns Sour
Under normal conditions, Candida coexists peacefully with beneficial bacteria in the crop. The trouble starts when that bacterial balance gets thrown off. The single most common trigger is prolonged oral antibiotic use, typically one to two weeks or longer. Antibiotics wipe out the beneficial bacteria that keep yeast in check, leaving open territory for Candida to colonize aggressively.
Other common causes include spoiled or moldy feed, slimy waterers, high-carbohydrate diets, and vitamin or protein deficiencies. A chicken that’s already immunocompromised from illness or stress is especially vulnerable. Crop stasis, where the crop stops emptying properly, also creates ideal conditions for fermentation. This is why sour crop frequently develops as a secondary problem after an impacted crop or a pendulous crop that has lost its muscle tone.
What Sour Crop Looks and Feels Like
The most obvious sign is the crop itself. Instead of feeling firm or gradually shrinking as food moves through, a sour crop feels like a small water balloon. It’s soft, squishy, and often visibly distended. If you pick the hen up and apply gentle pressure to the crop, liquid may spill out of her beak. That liquid often looks brown and has a distinctly foul, fermented smell, sometimes described as yeasty or rotten.
Affected hens often flick their heads repeatedly, trying to clear the uncomfortable fluid. You may also notice a decrease in appetite, lethargy, weight loss, and a general reluctance to move. The smell alone is often what alerts keepers to the problem. If you hold a chicken close and notice a sour odor coming from her mouth, that’s a strong indicator.
Sour Crop vs. Impacted Crop
These two conditions are easy to confuse because both involve an abnormal crop, but the physical feel is completely different. A sour crop is soft and fluid-filled, like a water balloon. An impacted crop is hard and firm, packed with material that can’t pass through to the stomach. Think of it as the difference between squeezing a bag of water and squeezing a bag of sand.
The distinction matters because impacted crop can actually lead to sour crop. When food sits stuck in the crop for too long, it begins to ferment, creating the perfect environment for yeast overgrowth. So if your chicken has a hard, firm crop that eventually becomes soft and foul-smelling, the impaction likely came first and sour crop developed on top of it. Treating just the yeast without addressing the underlying blockage won’t solve the problem.
How Sour Crop Is Treated
Mild cases caught early sometimes respond to simple dietary changes and natural support. Adding unfiltered apple cider vinegar to drinking water at roughly 1 teaspoon per liter can help restore a healthier pH in the crop, creating a less hospitable environment for yeast. Probiotics, whether from supplements or natural sources like plain yogurt, help repopulate beneficial bacteria.
For more established infections, the standard treatment is an antifungal medication that targets Candida directly. This medication works by contacting the yeast inside the crop rather than being absorbed into the bloodstream, so it needs to be given orally. A veterinarian can prescribe the appropriate course. Treatment typically needs to continue for several days even after symptoms improve, because stopping too early allows the yeast to bounce back.
During treatment, many keepers withhold regular feed temporarily and offer high-protein, low-carbohydrate foods instead. Scrambled eggs, canned tuna, and plain Greek yogurt are common choices. Carbohydrates feed yeast growth, so limiting them during recovery makes sense. Once the crop is emptying normally and the smell has resolved, regular feed can be gradually reintroduced.
Emptying the Crop Manually
Some keepers drain fluid from the crop by holding the chicken upright and gently massaging the crop upward to encourage the liquid to come out through the beak. This can provide temporary relief, but it carries a real risk. If fluid enters the airway instead of exiting cleanly through the mouth, the chicken can aspirate and develop pneumonia or suffocate. The bird should always be held with her head pointing downward during any attempt, and pressure should be gentle and gradual. If you’re not confident in the technique, this is better left to a vet.
Preventing Sour Crop
Most cases of sour crop are preventable with basic management practices. The biggest one: don’t use oral antibiotics longer than necessary, and never without a clear reason. Antibiotics are the leading driver of the microbial imbalance that lets Candida take over.
Beyond that, prevention comes down to keeping feed and water clean. Change water sources daily and scrub waterers regularly to prevent the slimy biofilm that harbors harmful organisms. Don’t feed spoiled food, and store feed in dry, sealed containers to prevent mold growth. A balanced diet with adequate protein and vitamins supports the immune system that keeps Candida in check naturally.
Some keepers add apple cider vinegar to drinking water preventively, at a rate of about 5 milliliters per liter, every other month. This periodic acidification of the crop environment may help keep yeast populations low. Avoid using it in metal waterers, as the acidity can cause corrosion. Chickens recovering from any illness should be kept separated until their immune systems are fully restored, since immunocompromised birds are the most vulnerable to opportunistic infections like candidiasis.