MINIMISING ODOUR AT THE SOURCE.
Good design and management practices are the keys to minimising odour from meat chicken sheds and for improving production (McGahan et al. 2002). Therefore, assessing current practices and shed features should be the first step in an odourreduction program.
The critical factors influencing odour generation are temperature, humidity, ventilation and the management of litter. Appropriate management of stocking rates, diet and waste products may also be relevant as outlined in the following sections. Where feasible, the number of birds should also correlate with the available separation distances.
1. Shed temperature and humidity.
Temperature influences the degradation of litter and the volatilisation of odorous compounds. Maintaining temperatures near to 22o C is also critical for bird welfare and production – healthy birds will produce drier and less odorous manure.
Strategies to save energy, reduce radiant heat and increase the cooling capacity of airflow within poultry sheds include:
- aligning the sheds along an east–west axis with large roof overhangs and shading ventilation openings to minimise exposure to direct solar radiation
- providing adequate roof (and wall) insulation
- maintaining mown grass cover or other vegetation around sheds to reduce ground radiation
- using effective cooling systems and ensuring ventilation openings and fans are free from obstruction
- keeping birds calm to minimise heat production: darkened sheds and green lighting can help do this
- in summer, reducing bird density if temperatures cannot be maintained.
2. Adequate shed ventilation.
Effective air exchange within the shed helps reduce shed temperatures and encourages optimal litter moisture levels by promoting bird health, reducing the need for fogging and increasing drying rates. Good ventilation also dilutes the concentration of odorous gases released to the outside air (McGahan et al. 2002).
Ventilation design should optimise bird comfort by taking into account the climate and stocking densities. The type of ventilation system may also influence the dispersal of odours in the landscape. Conventional sheds with side openings and internal stirring fans are more subject to local wind patterns than tunnel-ventilated sheds, where the air is basically exhausted in one direction.
When planning a new or expanded meat chicken farm, the risk of odour problems can be reduced by exhausting air away from the direction of prevailing winds, cold air drainage pathways, local residences or community facilities such as halls or sports grounds.
Odour can also be reduced by maintaining ventilation systems. Regularly removing dust buildup from screens, ventilation shafts or windbreak walls will improve operational efficiency and can reduce odours by improving bird health and maintaining drier litter. Minimising dust levels will also reduce odour transmission (McPherson 2000, McGahan et al. 2002).
3. Poultry litter moisture content.
Excessively wet litter is the main source of odour from meat chicken sheds. Jiang & Sands (2000) reported that reducing the moisture content within sheds and maintaining litter pH above 7.5 could effectively reduce odour emission from meat chicken sheds by inhibiting anaerobic bacterial activity.
The optimal shed litter moisture content to minimise odour generation and provide a healthy environment for workers and birds is between 15% and 30% (wet basis) (NSW Meat Chicken Guidelines, 2002).
Dietary upset caused by feed formulation, medication or poor bird health can produce extremely wet manure, high litter moisture content and odours. Regular monitoring and close communication between growers and chicken and feed suppliers (usually processors) can help reduce such problems.
On hot days, temperatures in conventional sheds are reduced by using fans and foggers to create a cooling mist. But extended or frequent fogger use unfortunately results in wet birds and litter, especially if foggers are poorly maintained causing uneven flow and leaks. Condensation due to poor insulation or ventilation also contributes to wet litter.
In controlled-environment sheds foggers may be used as a backup during extreme temperatures but the primary cooling devices are wind chill and external evaporative cooling pads. The increased airflow and improved feed conversion in tunnel-vented sheds further helps to maintain shed litter within the optimal moisture content range.
In all shed types poorly maintained drinking lines can create localised wet spots. Even quite small wet areas can significantly increase odour emissions and should be addressed by promptly repairing any faulty watering systems and either removing and replacing the wet litter or topping up with clean, dry bedding material.
Actions and shed designs which help ensure optimal litter moisture content include:
- effective cooling systems that provide optimum growing conditions and minimise the need to use internal foggers;
- monitoring and adjusting cooling systems and bird drinkers to avoid spillage, leaks and uneven distribution;
- appropriate stocking densities and attention to bird health;
- regularly breaking up and removing caked litter beneath drinking lines;
- adequate roof overhang and sidewall height to stop rainwater from entering the shed;
- insulating shed roofs to avoid internal condensation and promptly repairing any leaks in walls and roofs.
4. Dietary manipulation.
A study of the effects of reducing crude protein levels in feed and simultaneously enhancing dietary amino acid levels (reported in McGahan et al. 2002) found that, after three batches:
- the litter had a lower moisture content and pH;
- the relative concentrations of equilibrium ammonia gas and total ammoniacal nitrogen in the litter was lower (approximately 90% and 50% lower respectively); and
- production performance was not compromised (between 1.8 and 2 kg feed per kg liveweight gain).
However, studies of the correlation between ammonia reduction and odour emissions across a range of industries have produced conflicting results. While some studies have found that reducing ammonia can reduce odour levels, recent research on odour emission from meat chicken sheds (Jiang & Sands 2000) found no correlation between ammonia and odour concentration.
The variable outcomes may be due to a masking effect where the removal of one odour (e.g. ammonia) may allow other previously neutralised or less dominant odour compounds in the emissions to be detected. Empirical evidence also indicates that the peak period of ammonia generation may not correlate with the period of peak odour emissions and complaints.
Further research is required to assess the effectiveness of dietary manipulation as an odour control strategy.
5. Litter and dead bird management.
The removal of litter from poultry sheds will inevitably generate dust and odours. But the risk of odour impact is increased when mild breezes are blowing from the sheds towards nearby residences.
In the early morning or towards night, cold air drainage can also carry odours considerable distances downslope. Odour movement is also affected by temperature inversions and can reach relatively
distant residences. Wherever possible avoid handling litter in adverse climatic conditions.
If spent litter is applied on-farm, odour impacts can be minimised by careful selection of storage areas, assessing predicted wind direction and strength, avoiding adverse weather conditions and weekend work as well as applying litter at the correct rate. Incorporating the spent litter as soon as possible can also help. Recommendations for storing and using poultry litter are provided in the Agnote Best practice guidelines for using poultry litter on pastures.
Inappropriate handling of dead birds (e.g. substandard incinerators or composting practices) can also cause odour problems and complaints from neighbours. Dead birds should be collected from sheds each day and refrigerated or frozen if not immediately disposed of.
Recommended disposal options (subject to Council approval) include:
- composting in appropriately designed and managed litter heaps or in approved and appropriately maintained composters of suitable capacity;
- off-site disposal in an authorised landfill or recycling facility or on-site burial in a covered pit (located to avoid groundwater or surface water contamination); and
- incinerators of suitable capacity that have been approved and properly maintained.
Author.
Glenda Briggs.
