Sour crop symptoms and causes: candidiasis in poultry
is a candidiasis in poultry driven in almost all cases by a Candida albicans crop infection. The organism is a normal resident, not an invader. A survey of six grow out operations found Candida in 17.4 to 51.5 percent of healthy broiler crops, with lesions in fewer than 1 percent of birds (Wyatt and Hamilton, 1975).<
Disease follows disruption of the gut flora. Prolonged antimicrobial therapy, contaminated drinker lines, vitamin A deficiency and mycotoxin exposure are the recognised triggers (Merck Veterinary Manual, 2024). Affected birds show a doughy, distended crop, regurgitation, and white pseudomembranes on a thickened lining at post mortem (Butcher and Miles, 2009).
Crop impaction in poultry: impacted crop and pendulous crop
An impacted crop, also called crop binding, is a mechanical blockage rather than an infection. Long fibrous litter, coarse feed particles and abrupt feed withdrawal contribute. A commercial turkey flock of 7,800 poults lost birds to litter impaction traced to defective ventilation, insufficient drinkers and feeder height (Kaboudi et al., 2015).
Pendulous crop overlaps both conditions. Ebling et al. (2015) recorded 9.5 percent incidence in Cobb 500 broilers under continuous lighting and ad libitum feeding. In turkeys the heritability coefficient (h²) is 0.16 to 0.17 (Abdalla et al., 2022).
How to diagnose crop problems by palpation and crop emptying
A healthy crop empties every two to four hours (Classen et al., 2016). Delayed crop emptying outside that window is the first diagnostic signal.
Crop palpation is the standard diagnostic method, and it happens during manual weighing. A session with the BAT1 manual poultry scale puts every sampled bird in the hand, so crop condition and fleshing are judged alongside the recorded weight.
A crop fill score, on the other hand, measures how fast day-old chicks find feed and water after placement, not whether a crop is diseased. Aviagen (2025) targets 75 percent of chicks with full crops at two hours and 95 percent at 24 hours. Hard crops indicate water shortage, distended crops feed shortage (Cobb-Vantress, 2021).
Weight data as an early warning signal
Crop disorders cut feed intake before they are visually obvious, which appears as a growth check. Stunted broilers carrying digestive tract lesions weighed 28 to 33 percent less than normal flockmates between 11 and 40 days (Qamar et al., 2013).
Flock variability moves the same way. Poorer uniformity was associated with higher mortality and worse feed conversion across 45 commercial Ross 308 flocks (Vasdal et al., 2019), and microbial challenge can cut uniformity by 2.5 to 15 percent (Choi et al., 2026).
Catching that divergence needs frequent measurement. The BAT2 Connect automatic poultry scale records flock averages throughout the day, and Mels et al. (2023) used automatic weighing across 100 pullet flocks to support early detection of health problems.
Reviewing those trends in a central platform for flock performance data shows deviation against the target curve within days.
How to treat sour crop in chickens at flock level
No approved product exists for treating candidiasis in the United States, and nystatin availability varies by jurisdiction (Merck Veterinary Manual, 2024). Individual dosing is impractical at commercial scale, so control rests on removing the cause: water line sanitation, acidification, careful antibiotic use and mycotoxin management.
Impacted crop chicken treatment and bird level identification
Impaction has no pharmacological answer. Correcting litter length, feed particle size, drinker access and feeder height removes the cause, and blocked birds are culled. Affected birds in both conditions must be found first.
Weighing birds by hand makes that possible, because each bird is caught, held and examined individually.
Continuous flock average monitoring reports the trend but cannot single out an individual bird. The two methods answer different questions, and a crop investigation needs both.
References
Abdalla, B. A., et al. (2022). Accuracy of genomic selection for reducing susceptibility to pendulous crop in turkey. Poultry Science, 101(2), 101601. https://pmc.ncbi.nlm.nih.gov/articles/PMC8715376/
Aviagen. (2025). Ross Broiler Pocket Guide. https://aviagen.com/assets/Tech_Center/Ross_Broiler/Aviagen-ROSS-Broiler-PocketGuide-EN.pdf
Butcher, G. D., and Miles, R. D. (2009). Improved Aviculture Management May Prevent Candidiasis in Birds. University of Florida IFAS Extension, VM031. https://edis.ifas.ufl.edu/publication/VM031/pdf
Choi, J., et al. (2026). Factors Affecting Flock Uniformity in Broiler Production. Animals, 16(2), 185. https://www.mdpi.com/2076-2615/16/2/185
Classen, H. L., et al. (2016). The role of the crop in poultry production. World’s Poultry Science Journal. https://www.cambridge.org/core/journals/world-s-poultry-science-journal/article/role-of-the-crop-in-poultry-production/1B8129FC8897E3A1C9D4A0D074F65BB7
Cobb-Vantress. (2021). Broiler Management Guide. https://www.cobbgenetics.com/assets/Cobb-Files/Broiler-Guide_English-2021-min.pdf
Ebling, P. D., et al. (2015). Pendulous Crop in Broilers. Brazilian Journal of Poultry Science, 17, 395-398. https://www.scielo.br/j/rbca/a/cqQVTsCkyn4wXfnKzqHXvYc/?lang=en
Kaboudi, K., Umar, S., and Bouchrit, H. (2015). Outbreak of litter impaction of the gastrointestinal tract in commercial turkey poults. Journal of Avian Research, 1(2), 15-16. https://www.researchgate.net/publication/286452320
Mels, C., et al. (2023). Development and evaluation of an animal health and welfare monitoring system for veterinary supervision of pullet farms. Preventive Veterinary Medicine, 217, 105929. https://www.sciencedirect.com/science/article/pii/S0167587723000934
Merck Veterinary Manual. (2024). Candidiasis in Poultry. https://www.merckvetmanual.com/poultry/candidiasis-in-poultry/candidiasis-in-poultry
Qamar, M. F., Aslam, H., and Jahan, N. (2013). Histopathological Studies on Stunting Syndrome in Broilers. Veterinary Medicine International, 212830. https://pmc.ncbi.nlm.nih.gov/articles/PMC3732646/
Vasdal, G., et al. (2019). Associations between carcass weight uniformity and production measures on farm and at slaughter in commercial broiler flocks. Poultry Science, 98(10), 4261-4268. https://pmc.ncbi.nlm.nih.gov/articles/PMC6748757/
Wyatt, R. D., and Hamilton, P. B. (1975). Candida species and crop mycosis in broiler chickens. Poultry Science, 54(5), 1663-1666. https://pubmed.ncbi.nlm.nih.gov/1103110/