This document discusses litter quality, odour control, and airflow patterns in commercial broiler production facilities. Poor litter quality can lead to increased odours and toxic gases from bird waste. Litter quality is affected by factors like feed quality, management practices, and environmental conditions. Controlling odours involves varying ventilation rates to control moisture and gases, and using chemicals to reduce bacteria growth. Airflow patterns within the facility are important to distribute air temperature evenly and reduce moisture buildup. Litter pH reflects airflow and affects ammonia emission, so measuring pH can help evaluate ventilation effectiveness.

1. 32 POULTRY INTERNATIONAL MAY 2002
O
ne of the biggest problems facing commercial
broiler producers today is odour control on
the farm. Most odours come from the birds’
waste and decomposition of the litter. Poor litter
quality can lead to reduced bird performance and
high levels of toxic gases, e.g. ammonia, carbon
dioxide and hydrogen sulphide.
Factors affecting litter quality
• feed, e.g. poor quality fat, excess salt and protein
• management, e.g. insufficient litter at start,
inappropriate material, spillage, excessive stocking
density
• environment, e.g. low ventilation rate, high levels
of toxic gases, humidity and high temperature.
Controlling odours
• by varying ventilation rates over the growing
period. Ventilation is a cost-effective and easy way to
minimise odour and toxic gases, weather permitting.
The ventilation rate should be set to control litter
moisture and odour release from manure.
• by using chemicals. These are sprayed in the shed
on a timed basis (several seconds per minute) or
applied onto the litter as a powder every one or two
weeks. Their aim is to minimise the growth of bacteria
or to break down the elements causing the odour.
Sprays not only improve conditions inside the house
but also minimise odour outside the shed.
Air flow patterns
The flow pattern within the building is very
important. Fans within the house control air
movement and the way air enters the building.
Circulating the air within the house should create a
uniform temperature. Mixing of the incoming and
inside air prevents the cooler air from settling near
the litter, chilling the birds in winter. It also reduces
the release of moisture from the litter, leading to a
build-up of moisture, microbial growth and
ammonia.
The most important factors affecting ammonia
production are environmental temperature, litter
moisture and its pH, air velocity, and temperature.
Litter pH has an important influence on ammonia
emission. An effective way of reducing pH is to acidify
the litter. Humans can perceive ammonia as low as 10
ppm. However, extended exposure to the gas reduces
the sensitivity of perception and consequently flock
managers are not always aware of the ammonia in the
broiler house.
Relationship between litter pH and
airflow
Ammonia production can be cut by reducing litter
with products. Firstly, pH must be measured over a
period of time in order to evaluate the efficacy of the
product. It also gives a guide to the ventilation
pattern in the house because the moving air leaves a
“footprint” on the litter by changing the pH. In
summer, incoming air is directed towards the birds to
cool them and to dry out the litter.
Manipulation of the inlets or flaps will influence
the direction (orientation) of the incoming air. If the
air hits the litter in the first quarter of the house, it will
“bounce” and change direction (as shown in Figure
1). The first quarter is usually cooler and drier
than the rest of the house and the pH value
will be lower.
If the air hits the middle of the house first, which is
preferred, the cooling effect of the air will be more
evenly distributed, and the litter will be drier in the
middle of the house than elsewhere (lower pH, see
Figure 2). If the air hits the litter too far or close to the
fans, this side will be drier and the pH value will be
lower. In this case the cooling effect of the air will not
be used properly, because the fans will suck the air
out (figure 3). To get around this problem, circulating
fans can be set up in the corners of the house move
Correlation between litter
pH and airflow pattern
Litter pH closely reflects the airflow pattern in a broiler house. These factors
play an important role in controlling ammonia level and odour – two very
sensitive areas with local residents. — Dr Dhia Alchalabi
Figure 1: Poor airflow pattern in a house with side outlet
– incoming air drops too soon

2. the air in these
places. Please see
illustrations.
The pH pattern
is different in a
house which is
ventilated across
sections rather
than in the ridge
(see figure 4 on
page 44).The pH is usually higher at the sides than in the middle of the house.
This pattern may be different in tunnel ventilated houses the litter will be
drier at the end of the house near the inlets and the opposite close to the fans.
In winter, cold air is directed to the ceiling to be warmed up and to reduce its
speed (figure 5 on page 44). The incoming air should have enough speed (2-3
m/sec) so that it is
mixed and does
not simply drop
on the birds,
creating a lot of
p r o b l e m s
including wet
litter.
The pH of the
litter is usually
low when the
Figure 3: Same house with air dropping too slowly from
inlet
Figure 2: Same house with ideal airflow pattern in summer

3. litter is new and gradually increases. Adjusting the
ventilation rate and air speed to move the air in the
house and dry the litter can slow this change. The
higher the pH, the greater the release of ammonia
and other gases.
How to measure litter pH
This is very simple. The acidity of the litter at each
point is measured using a pH meter. To decide on the
sampling points (see figure 6), start from one corner.
Take samples across the width of the house and
continue the length of the house in a zigzag pattern to
cover all the floor area.
How many samples are needed? Divide the length
of the house by ten to give the number of samples in
each line. Multiply this number by five to give the
number of samples across the house. This will give
you a total number of samples. A minimum of 25
samples will give a sound result. You can reduce the
number of samples by increasing the distance
between them, if necessary.
Constructing a spreadsheet for the data will allow
the results to be analysed statistically and compared
over time. Figure 7 shows an example.
Comparing results
Figure 8 shows the results of pH measurements
taken under different conditions across poultry
houses. Each point represents a mean of eight values
along the length of the house. Lines A and B represent
houses with outlets in the ridge and side wall,
respectively. It is easy to see the similar pattern to
those for airflow in figures 4 and 2, respectively. Line
C demonstrates the effects on pH of incoming air
dropping too soon from the inlet and flowing over the
floor area. When the inlet settings for the house with
side extraction were changed, the resulting pH vlaues
are represented by lines D and E. In a test house, an
odour control product (HI-Tech Pure Air) was applied
to the litter. The pH pattern of a similar but untreated
Correlation between litter pH and airflow pattern
Figure 4: Ideal airflow pattern in a house with outlet in
central ridge outlet
Figure 5: Ideal airflow pattern for a house in winter
Figure 6 Sampling pattern for litter pH profiling
Sample areas
5 4 3 2 1
Row 1 8.78 8.53 8.63 8.53 9.10
Row 2 8.71 8.63 8.46 8.20 8.60
Row 3 8.41 8.22 8.34 8.53 8.47
Row 4 8.50 8.53 8.28 8.35 8.60
Row 5 8.76 8.51 8.42 8.78 8.53
Row 6 8.79 8.19 8.16 7.91 8.36
Row 7 6.79 6.64 6.63 6.81 7.31
Row 8 7.23 6.71 6.56 6.61 6.76
Average 8.25 8.00 7.94 7.97 8.22
Figure 7: Plotting pH values across the house; an
example. Each point on the graph represents the average
of eight locations along the house length, as shown in the
table.

4. is shown by line E and
the treated house by
line F. The houses
contained the same
number of birds of the
same age. The
reduction in pH with
the odour-control
product is very clear.
Ways to control
ammonia levels
The level of
atmospheric ammonia
in a house is affected
by a number of
factors. In buildings
that are cleaned after
each flock, ammonia content generally increases
during the production cycle. Management practices
such as partial room brooding (use of only a
proportion of the house area during brooding) and
the use of the same litter for more than one flock can
have an important impact on ammonia production
during the production cycle. For example, the
combination of high brooding temperature, low
ventilation rate and re-using litter can result in very
high levels of ammonia early in the broiler
production cycle.
• Reducing litter
moisture an important way to reduce ammonia in a
broiler house.
• As litter
moisture is in equilibrium with relative humidity,
increasing the ventilation rate will help. Ventilation
also “dilutes” atmospheric ammonia by bringing
fresh air into the house. Similarly, litter moisture
rises as the result of condensation during cold
weather if ventilation is poor.
• Drinkers should be properly adjusted and
maintained to minimise spillage.
• Nutrition
influences faecal dry
matter content,
which tends to be
decreased by feeds
containing high
protein and sodium
or ingredients with a
high soluble fibre
content. High
dietary protein also
increases uric acid
excretion and
thereby yields more
substrate for the
production of
ammonia by
microbes.
• Digestive diseases cause diarrhoea and increase
faecal moisture output.
• Litter additives - Litter pH affects enzymatic and
microbial activities and pH has been manipulated
with some success by using additives to control
ammonia production. The objective is to reduce
litter pH to 7.0. Products tested include
monocalcium phosphate, and phosphoric, acetic
and propionic acids. Their efficacy tends to be short-
lived - pH and ammonia production return to pre-
treatment levels in 2-3 weeks. However, the
treatments hold some promise for winter flocks near
the end of a production cycle. Other litter
applications, e.g. paraformaldehyde, zeolites and
yucca saponin, combine with the ammonia to
neutralise it. Paraformaldehyde also has a well-
documented anti-microbial effect that may reduce
ammonia production.
— Dr Dhia Alchalabi, Associate Professor /
Consultant in Poultry Environment and Odour
Control, New Zealand
HI-Tech Pure Air is a product based on plant and
fruit juice from New Zealand.
Correlation between litter pH and airflow pattern
Figure 8: Comparing pH values across the house under different
conditions