Wet litter — causes and effects (FPD and hock burn)
Dry, friable litter is the foundation of broiler leg and skin health. When litter becomes wet and caked — from urine, droppings and condensing moisture — it starts damaging the birds’ skin and releases ammonia. We explain where wet litter comes from and what it costs the farmer and the bird.
verifiedFrom the team that has organised work on poultry farms for years.
Wet litter is one of the most common problems in broiler farming. Its effects are not immediately visible — for the first weeks everything may look normal. It is only at collection or at the slaughterhouse that the farmer finds out the birds had damaged footpads and hocks, and that the price per kilogram will be deducted accordingly. That is why litter quality is a daily task, not an exception.
What are FPD and hock burn?
FPD (footpad dermatitis) is skin damage on the underside of the bird's foot — where the foot touches the floor. It looks like dark spots, ulcers or scabs. Hock burn is discolouration and skin damage on the hock joint — the bend of the leg roughly halfway up. Both conditions result from prolonged contact of the skin with wet, acidic litter. In Poland, FPD and hock burn scores affect the purchase price directly — the worse the footpads, the larger the deduction. More on scoring and assessment in the guide on pododermatitis — broiler footpad quality.
How to check whether litter is too wet?
The simplest test is to take a handful of litter and squeeze. If it crumbles when you open your hand — it is dry and good. If it clumps together — it is too wet. The indicative upper moisture threshold at which FPD risk is clearly lower is roughly 30%, but the handful test is faster than any measurement and is sufficient for daily monitoring. Litter management details are in the guide on litter in the poultry house — management.
What causes wet litter in a broiler house
Wet litter rarely has a single cause. Most often it is a combination — drinkers, ventilation and gut health all interact. Below are the key causes.
Leaking or incorrectly set drinkers
Nipple drinkers are the main water source in the house — and the main source of wet litter when something goes wrong. A dripping nipple over 24 hours delivers enough water to wet the litter beneath it within hours. Incorrect height has a similar effect — when the drinker is too low, the bird has to twist and water spills. Check that nipples are not dripping, that water pressure is correct and that drinker height is adjusted every few days as the birds grow. More on water consumption monitoring in the guide on water use in broilers.
Insufficient ventilation or poor moisture control
Broilers exhale water vapour with every breath and release moisture in their droppings. In a house of 20,000 birds this is an enormous volume of water every day. If ventilation does not remove this moisture fast enough, it condenses on cold walls, floors and the litter itself. The result: litter becomes wet from above even when drinkers are in perfect condition. This is especially dangerous in winter when farmers reduce ventilation to save on heating. Ventilation principles are described in the guide on broiler house ventilation.
Diarrhoea — disease, poor feed or excess salt
When a bird has diarrhoea its droppings contain far more water than normal. Litter under the birds wets very quickly and cannot dry out even with good ventilation. Diarrhoea can have various causes: intestinal disease (e.g. coccidiosis), excess salt or protein in the feed, poor water quality or a sudden feed change. Always check feed and water when litter starts wetting unexpectedly.
Overstocking
The more birds per square metre, the more moisture, heat and droppings on the same area of litter. The litter simply cannot keep up with drying. High stocking density also increases stress, which lowers immunity — and that promotes diarrhoea. European welfare regulations set maximum stocking densities, but even near the upper limits the risk of wet litter rises noticeably. Stocking density also directly affects FPD scores at collection — as described in the guide on poultry welfare indicators.
Poor litter quality or insufficient depth
Litter must absorb moisture and allow it to evaporate. If it is caked, wet or too thin (less than a few centimetres), it cannot do this. Some litter materials — e.g. coarsely chopped straw or shavings with a lot of bark — absorb moisture less effectively. Caked, matted litter does not dry even with good ventilation — it needs to be broken up or replaced.
Cold floor without heating
When the floor is cold (e.g. at the start of a cycle or after a production break), moisture condenses on its surface and wets the bottom layer of litter from below. Birds lying on cold, damp litter develop FPD faster. Underfloor heating or proper pre-warming of the house before chick placement reduces this problem.
Effects of wet litter on bird health and farm results
Wet litter is not just an aesthetic problem. Its consequences show up in bird health, growth performance and — above all — in the settlement with the buyer.
FPD and hock burn — footpad and hock skin damage
Prolonged contact of the footpad skin with wet, acidic litter causes footpad dermatitis (FPD) — dark spots, ulcers and scabs on the underside of the foot. A similar mechanism damages the hock joints (hock burn). Both conditions are painful: a bird with severe FPD moves less, spends less time at the feeder and eats less. This means poorer weight gain and a higher feed conversion ratio.
Price deductions at the slaughterhouse
In Poland, slaughterhouses assess footpad and hock quality at every delivery. FPD and hock burn scores translate directly into the purchase price — the worse the footpads, the larger the deduction per kilogram. In a poor batch the losses can be significant and often surprise farmers who have not been monitoring litter quality daily.
Ammonia irritates the respiratory tract and eyes
Wet litter ferments and releases ammonia — a sharp, pungent gas noticeable when entering the house. Ammonia irritates the mucous membranes of the birds' eyes, throat and respiratory tract. This lowers immunity and promotes respiratory infections. Farmers working regularly in houses with high ammonia concentrations also experience eye irritation and discomfort — a sign that conditions exceed safe levels.
Poorer growth and higher disease susceptibility
A bird in pain or discomfort does not forage as actively and does not rest as effectively. Poor living conditions lead to slower growth, a higher feed conversion ratio (FCR) and greater susceptibility to various diseases. Wet litter also creates an environment that favours the multiplication of pathogens — bacteria and protozoa causing intestinal disease.
How to keep litter dry — daily actions
Dry litter is the result of several actions together: drinker checks, ventilation, gut health and regular breaking up. Below are the key principles.
Check drinkers every day
Once a day look for wet patches under the drinkers. Check a few nipples from different zones. If a nipple is dripping — repair or replace it. Adjust drinker height every few days — a drinker hung too low is a direct cause of wet litter. Drinker checks take a few minutes and can save FPD scores and purchase deductions.
Maintain ventilation, even in winter
Ventilation must run continuously — even when it is cold outside. If you reduce it to save on heating, moisture stays in the house and condenses on the litter. A better approach is to maintain minimum air throughput around the clock and to pre-heat incoming air rather than closing inlets completely. Ventilation principles are described in the guide on broiler house ventilation.
Monitor gut health and feed quality
Diarrhoea is an immediate alarm — wet litter appears very quickly. At the first signs of diarrhoea check the water (cleanliness, pH), the feed (freshness, composition, especially salt and protein content) and flock health. A fast response limits the time litter is exposed to extreme moisture.
Break up litter and quickly replace caked patches
Caked, matted litter does not dry out — even if ventilation is working well. Mechanical or manual breaking up loosens the top layer and allows moisture to evaporate. The most critical areas are under drinkers and near air inlets — litter wets fastest there. These are also the areas that most often need fresh litter added or the whole layer replaced.
Match stocking density and prepare the house before placement
Too high a stocking density not only increases the risk of wet litter — it also reduces effective ventilation and raises the risk of stress and disease. Before each chick placement make sure the floor is dry and warm — a cold floor means a wet bottom layer of litter in the very first days, which is particularly harmful to young chicks.
Common mistakes in litter management
A few typical errors that allow wet litter problems to build up unnoticed until collection.
Reducing ventilation in winter "to save money"
This is the most common mistake. The farmer reduces ventilation on cold days because heating is expensive. Moisture stays in the house, litter gets wet and ammonia rises. The result: weaker birds, worse footpads and purchase deductions that cost more than the fuel saved. The minimum ventilation rate must be maintained around the clock, regardless of outside temperature.
No daily check under drinkers
A dripping nipple over a week can wet a significant area of litter. If the farmer checks litter condition only occasionally — e.g. once a week — the problem has time to develop. A quick daily look under each drinker line takes a few minutes and catches faults before they cause damage.
Delaying action on diarrhoea
Diarrhoea is a sudden and intense source of moisture in the litter. Every day of delay means wet litter spreading over a larger area. At the first signs of diarrhoea — changed appearance of droppings, wet patches under birds — act immediately: check feed, water and flock health, and break up or replace litter in wet sections.
Ignoring caked patches under drinkers
Litter under drinkers wets fastest and cakes into a hard, wet layer — and birds rest there most often (close to water). This is where FPD and hock burn develop fastest. Regularly replacing or topping up fresh litter in these specific spots is one of the simplest ways to lower FPD scores.
Frequently asked questions about wet litter and FPD
What are FPD and hock burn?add
FPD (footpad dermatitis) is skin damage on the underside of the broiler's foot — where the foot contacts the floor. It looks like dark spots, ulcers or scabs and can be painful. Hock burn is discolouration and skin damage on the hock joint (the bend of the leg, roughly halfway up). Both conditions result from prolonged contact of the skin with wet, acidic litter and are assessed at collection — the worse the scores, the larger the price deduction.
What causes wet litter in a broiler house?add
The most common causes are: leaking or incorrectly set drinkers (water spills onto litter), insufficient ventilation (moisture from bird breathing and droppings condenses in the house), diarrhoea (droppings contain too much water, e.g. from intestinal disease or poor feed), overstocking, and poor litter quality or insufficient depth. In practice several of these factors usually act simultaneously.
How do you check if litter is too wet?add
The simplest test is a handful: take some litter, squeeze it, and release. If it crumbles — it is good. If it clumps — it is too wet. The indicative moisture threshold above which FPD risk rises clearly is around 30%, but the handful test is sufficient for daily monitoring and requires no equipment.
Why is ammonia from wet litter dangerous to birds?add
Wet litter ferments and produces ammonia — a sharp, pungent gas. It irritates the mucous membranes of the birds' respiratory tract and eyes, lowers immunity and promotes respiratory infections. High ammonia concentration is noticeable when entering the house — a sign that ventilation is too weak or litter is too wet. Farmers working regularly in such conditions also experience eye irritation and throat discomfort.
Does wet litter affect the purchase price?add
Yes, directly. In Poland slaughterhouses assess footpad and hock quality at every delivery. FPD and hock burn — which develop from contact with wet litter — translate into price deductions per kilogram. The worse the footpad scores, the lower the price. Litter quality is therefore not only a welfare issue but straightforward farm economics.
What should I do when litter starts getting wet?add
Act immediately on several fronts: check drinkers (dripping nipples, height setting), assess ventilation (whether airflow is sufficient), inspect droppings for signs of diarrhoea. Break up or replace caked, wet patches of litter with fresh material. The faster you respond, the smaller the area of damaged litter and the fewer birds exposed to wet flooring.
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