Chickens develop diarrhea for a wide range of reasons, from harmless dietary changes to serious infections that can spread through an entire flock. The first thing to figure out is whether what you’re seeing is actually diarrhea or just a normal cecal dropping, because chickens produce a stickier, darker type of poop several times a day that looks alarming but is completely healthy. If the droppings are truly watery, bloody, or foul-smelling, something is going on that needs your attention.
Cecal Droppings vs. Actual Diarrhea
Chickens have two types of normal droppings. Regular droppings are firm with a white cap of urates on top. Cecal droppings, which happen several times a day, are thicker, stickier, darker (often mustard or chocolate colored), and smell noticeably worse. They come from the ceca, two pouches in the digestive tract that ferment plant material. Cecal droppings are a sign the digestive system is working properly, not a sign of illness.
True diarrhea looks different. The droppings will be consistently watery rather than just occasionally loose. Watch for blood or red streaks, unusual amounts of mucus, bright green or yellow coloring, or a persistent foul smell that goes beyond normal cecal odor. If you’re seeing these signs across multiple droppings over the course of a day, it’s time to investigate further.
Coccidiosis: The Most Common Culprit
Coccidiosis is the single most frequent cause of diarrhea in chickens, especially in young birds under three months old. It’s caused by tiny parasites called Eimeria that invade the cells lining the intestinal wall. The disease moves fast, running its course in just four to seven days, and in that short window it can cause extensive damage to the gut lining. In severe cases, the intestinal wall swells to more than double its normal diameter and fills with blood, mucus, and fluid.
The signs go beyond loose stool. Birds with coccidiosis eat and drink less, lose weight rapidly, become lethargic, and develop ruffled feathers. The droppings are often watery and mucoid. Bloody droppings are a hallmark of the more aggressive Eimeria species, which burrow deep into the intestinal wall and cause hemorrhaging. You may also notice excess mucus in the stool as the gut tries to protect itself by coating the intestinal lining.
Coccidiosis spreads through contaminated droppings in wet, warm litter. Overcrowded coops with poor ventilation create ideal conditions. Treatment involves adding an anti-coccidial medication to the drinking water for three to five days, followed by a lower maintenance dose for another one to two weeks. Catching it early makes a significant difference in survival, so don’t wait to act if you suspect it.
Bacterial Infections
E. coli and Salmonella are the two bacterial infections that most commonly cause diarrhea in backyard flocks. Both can produce watery or bloody droppings, and both tend to come on when birds are already stressed from overcrowding, dirty water, or poor nutrition. E. coli infections often show up as a secondary problem after another illness has already weakened the bird’s defenses.
Worth noting: Salmonella in chickens is also a human health concern. Infected birds can shed the bacteria in their droppings without looking obviously sick. If you handle a bird with diarrhea, wash your hands thoroughly afterward. Salmonella in people causes fever, stomach cramps, and diarrhea that can become serious if it lasts more than three days or includes blood.
Vent Gleet and Fungal Issues
If your chicken’s diarrhea comes with a strong, foul smell and a crusty, inflamed vent area, vent gleet is a likely cause. This is an inflammation of the cloaca (the opening where droppings, eggs, and urine all exit) that can be triggered by bacterial, fungal, or parasitic infections. Candida, the same type of yeast that causes thrush in humans, is one of the more common fungal causes.
Signs of vent gleet include difficulty passing feces, white chalky buildup on the feathers below the vent, excessive picking or grooming around the vent, and droppings that smell far worse than usual. Birds may also become lethargic and eat less. Vent gleet can look like simple diarrhea at first, but the vent inflammation and smell are distinctive. Cleaning the area gently with warm water and addressing the underlying infection are the first steps toward recovery.
Heat Stress and Excess Water
On hot days, chickens pant more, eat less, and drink significantly more water. That spike in water intake alone can produce loose, watery droppings that look like diarrhea but are really just the result of fluid overload. If your birds seem otherwise active and healthy but their droppings get runny during a heat wave, this is probably what’s happening.
Heat stress does more than just change water intake, though. Reduced feed consumption and increased drinking alter the balance of nutrients in the gut, which shifts the microbial environment and can affect intestinal motility and secretion patterns. If the loose droppings resolve once temperatures drop and the birds return to normal eating and drinking, heat was likely the issue. Providing shade, cool water, and good ventilation is the fix.
Diet Problems
Sudden changes in feed, too many kitchen scraps, or an unbalanced diet can all trigger loose stools. Excess protein is a particular offender. Research in young pigs (a useful comparison for understanding gut inflammation in livestock) found that diets with protein levels well above normal triggered intestinal inflammation and persistent diarrhea within about 12 days, along with reduced feed intake. Chickens aren’t pigs, but the underlying mechanism of gut irritation from excess protein applies across species.
The most common dietary triggers in backyard flocks are overfeeding treats like fruits, vegetables, and table scraps. These add moisture and can throw off the nutritional balance of a formulated feed. A good rule of thumb is to keep treats to no more than 10% of total intake. If you recently switched feeds or introduced a new food and the diarrhea started shortly after, try going back to the previous diet and see if things firm up within a day or two.
Worms and Other Parasites
Internal parasites like roundworms, tapeworms, and giardia all cause diarrhea in chickens. Heavy worm burdens damage the intestinal lining, reduce nutrient absorption, and produce chronic loose stools that may contain visible worms in severe cases. Birds with worm infestations often look thin despite eating normally, and their combs may appear pale.
Regular fecal testing through a veterinarian is the most reliable way to diagnose worms. Many backyard flock keepers deworm on a schedule, but targeted treatment based on actual fecal results is more effective and avoids building parasite resistance to deworming medications.
Supporting Gut Recovery
Once you’ve addressed the underlying cause, helping the gut recover speeds the return to normal droppings. Probiotics are one of the most effective tools for this. Lactobacillus and Bacillus species are the workhorses of poultry gut health. Bacillus subtilis increases populations of beneficial Lactobacillus bacteria, boosts production of butyrate (a fatty acid that feeds intestinal cells), and helps regulate inflammation during gut infections. Adding a poultry-specific probiotic to feed or water after an illness can help reestablish a healthy microbial balance.
Research has also shown that combining Lactobacillus and Bifidobacterium strains reduces the load of harmful bacteria while improving overall gut function and feed efficiency. These aren’t miracle cures, but they give the digestive tract a meaningful head start in rebuilding after damage from infection or stress. Look for poultry probiotics at your local feed store rather than using human supplements, which aren’t formulated for a chicken’s digestive system.
When to Isolate or Seek Help
Two categories of signs should prompt quick action. The first is appearance changes: a pale or shrunken comb, ruffled feathers, dull eyes, or a hunched posture. The second is behavior changes: refusal to eat, lethargy, standing apart from the flock, or a sudden drop in egg production. Any of these combined with persistent diarrhea points to something more than a dietary upset.
Isolate a sick bird immediately to prevent potential spread to the rest of the flock. Bloody diarrhea, rapid weight loss, labored breathing, inability to stand, or sudden deaths in multiple birds all call for veterinary help right away. Highly contagious diseases can move through a flock in days, and early intervention is often the difference between losing one bird and losing many.