Zoom Out Series: Part 1
Understanding Spotty Liver Disease (SLD)
The silent production-killer in free-range laying hens.
Howdy y'all — today I want to dive into Spotty Liver Disease (SLD). This is a condition that doesn't get talked about much outside of veterinary circles, but it deserves your full attention—especially if you manage free-range or backyard layers.
SLD is caused by the bacterium Campylobacter hepaticus. While related to common food-safety bacteria, this specific pathogen is a specialist: it targets the liver of laying hens during their most productive cycles.
🔍 Pathology Breakdown: Why "Spotty"?
As the name suggests, the hallmark of this disease is the presence of distinctive, small (1-2mm), pale "spots" across the surface of the liver. These aren't just surface marks; they are areas of necrosis—localized tissue death where the bacteria have successfully attacked the organ.
Because this is an acute infectious disease, it moves fast. It’s not uncommon for a flock owner to find birds deceased before they ever showed symptoms of being "off."
The Path of Infection
The primary route for C. hepaticus is environmental contamination. It is shed in feces, meaning it spreads through the "fecal-oral" route—foraging in contaminated soil, pecking at shared surfaces, or drinking from tainted water sources.
While the soil is the main reservoir, current research is also investigating vertical transmission (through the egg itself) or contamination of the eggshell. This makes it a difficult pathogen to completely "fence out" of a system.
The "Perfect Storm" for an Outbreak
Peak Production
Hens are at their highest metabolic stress when they hit peak lay.
Heat Stress
Outbreaks often cluster in warmer months when the immune system is taxed.
Outdoor Access
Free-range systems have the highest exposure to soil-borne reservoirs.
The Danger of Misdiagnosis
One of the most frustrating aspects of SLD is that it mimics other issues. Because it strikes during peak lay and often in summer, many keepers mistake the sudden deaths or drop in production for simple heat stress or nutritional deficiencies. By the time they realize it's infectious, the bacteria have already established a foothold in the flock.
Conclusion: Stay Vigilant
SLD is no longer just an "Australian problem" or a "commercial problem." It is a global reality for anyone with birds on the ground. If you see a sudden, unexplained drop in egg production (typically 5-10%) or sporadic mortality in otherwise healthy-looking hens, C. hepaticus should be high on your list of suspects.
- Van et al. (2016). Campylobacter hepaticus sp. nov., isolated from chickens with spotty liver disease.
- Phung et al. (2020). Survival of Campylobacter hepaticus in the environment.
- Crawshaw, T. (2019). Review of Spotty Liver Disease in Laying Hens.