Wet litter and ammonia in a naturally ventilated broiler house
A 12 m × 60 m open-sided broiler house holds about 6,000 birds (roughly 8 birds/m²). It is the third flock in the house. Litter is wet and capped around the drinker lines and along the windward wall, ammonia stings the eyes at bird level, and birds pant in the afternoon even at 28 °C. Mortality is 6 % against a 4 % target, and feed conversion is 1.95 against 1.80. The house runs east–west, has a 1.2 m solid block wall on the south (windward) side, and a 3 m hedge of trees stands 4 m from the north side. Drinker lines were raised during the last flock and several nipples drip. Litter is 4 cm of fresh wood shavings. The farm's borehole is 25 m from the proposed manure heap, which is upslope of it.
1. Diagnose the problem. Separate structural causes from management causes, and explain how the ammonia and heat are hitting performance.
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Structural causes
- The 1.2 m solid block wall on the windward side blocks the low-level inlet. Air enters above bird level and does not sweep the litter, so the floor layer stays humid and ammonia accumulates.
- The 3 m hedge only 4 m from the leeward side throttles the outlet. Natural cross ventilation needs an unobstructed outlet at least as large as the inlet; with both sides restricted, the house depends on leakage.
- Stocking density is not the main culprit: 8 birds/m² in 720 m² is within normal range for a naturally ventilated house in a hot climate.
Management causes
- Drinkers were raised last flock and several nipples drip. Wet litter in rings around the drinker line is a management signature, not a ventilation one.
- Only 4 cm of litter is too shallow to absorb water and dilute droppings; 8–10 cm of dry shavings is normal.
Effects on performance Ammonia above about 25 ppm damages the respiratory tract and eyes, increases disease susceptibility and depresses feed intake, which shows up as feed conversion 1.95 instead of 1.80. Panting at only 28 °C means the birds cannot lose heat because the air is still and humid. Mortality of 6 % against 4 % fits secondary respiratory disease.
How to tell the two apart: structural faults give a gradient (worse near the solid wall and the hedge); management faults are localised (wet rings at drinkers). This house has both.
2. Give a ranked action plan: what to do for this flock now, and what to change before the next placement. Justify the order.
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This flock - act now, no rebuilding
- Fix the water. Lower the drinker lines to the correct height for the birds' age, replace the leaking nipples and check the pressure regulator. This is the cheapest fix and works within a day; leaking nipples are the main source of wet litter.
- Remove the worst litter. Take out the capped, wet litter around the drinkers and along the wall and replace it with dry shavings; stir or turn the rest weekly. Do not simply add fresh litter on top of a wet, capped layer.
- Get air moving. Open any shutters or netting, lower the blocked section of the windward wall to a 0.3–0.4 m solid base with an open inlet above it, and cut the hedge back to at least 10 m from the wall, especially on the leeward side. Add temporary fans on hot afternoons if available.
- Reduce the demand. If the flock is close to marketing, sell earlier rather than fighting the environment; consider thinning if any pen is overcrowded.
- Monitor. Use the nose test or a meter for ammonia at bird height, check litter condition, watch the water meter (a sudden rise means leaks) and record daily mortality and feed intake.
Before the next placement Rebuild the side wall as an adjustable open inlet over a 0.3–0.4 m solid base, add a ridge vent or opening, extend the roof overhang to about 1 m, keep the leeward side fully open, lay 8–10 cm of dry litter, service the drinker line and regulator, and repair apron drainage so rainwater cannot run in.
Why this order: management fixes cost little and give most of the benefit this flock; structural work can only be done between flocks.
3. Assess the siting of the manure heap 25 m from the borehole and upslope of it. Specify a better arrangement and how the litter should be spread.
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Assessment: too close, and on the wrong side of the slope. Rain running through the heap will carry nitrate, phosphorus, salts and pathogens downslope into the borehole, which supplies the farm's drinking and chick water. A shallow borehole or well is especially at risk, and boiling does not remove nitrate. Phosphorus travels attached to soil particles and will contaminate surface drainage; a heap on bare soil has nothing to intercept it.
Better arrangement
- Move the heap to a level, well-drained site at least 50 m from any borehole, well or watercourse - 100 m if the soil is sandy or the water table is shallow - and preferably downslope of the water point, not above it.
- Stand it on a concrete or compacted clay pad with a low bund and a roof or tarpaulin, so rain cannot leach through and run-off can be collected.
- Compost properly: turn the heap, keep it moist but not wet, and cover it; composting kills many pathogens and reduces bulk. Stockpile for at least 6–8 weeks before spreading, and never spread fresh litter on vegetables.
- Spread at a rate set by the soil test and the crop's nitrogen requirement. Broiler litter is roughly 2–3 % nitrogen, so 2–3 t/ha supplies a useful part of a maize crop's nitrogen; applying far more than the crop can use simply moves nitrate towards groundwater. Incorporate soon after spreading and avoid spreading before heavy rain.
- Keep records of quantities and dates, and have the borehole water tested for nitrate and coliforms once a year.