Generation of Airborne Particles from Different Bedding Materials Used for Horse Keeping
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ORIGINAL RESEARCH REFEREED
Generation of Airborne Particles from Different
Bedding Materials Used for Horse Keeping
K. Fleming, MSc, E.F. Hessel, PD Dr, and H.F.A. Van den Weghe, Prof Dr Ir
ABSTRACT Keywords: Horse keeping; Bedding material; Dust;
Airborne particles
Among other factors (eg, feed), bedding material has an
important effect on stable air quality with respect to air-
borne particle formation. This study was designed to es- INTRODUCTION
tablish which material is suited to create an improved Many horses spend the majority of their lives, up to 23
stable environment for horses. First, the following mate- hours per day, in their stall, where they are exposed to
rials were analyzed under standardized conditions in high particle loads.1 Air quality in horse stables is important
a laboratory experiment: wheat straw, dry wood to the health of horses, because several equine respiratory
shavings, hemp shives, linen shives, wheat straw pellets, disorders are directly caused or exacerbated by inhalation
paper cuttings (unprinted newspaper). The second in- of airborne particles. Gerber et al2 ascertained in their study
vestigation was carried out under in situ conditions in that all examined horses housed in a conventional stable
which three of these bedding materials (wheat straw, environment showed evidence of inflammatory airway dis-
wood shavings, and straw pellets) were analyzed under ease although they were clinically healthy and performed
practical conditions. In both experiments, airborne well. Holcombe et al3 established that stabling is associated
particle concentrations were detected online with the with lower airway inflammation and persistence of upper
gravimetrically measuring analyzer TEOM 1400a airway inflammation of young horses. They demonstrated
(Rupprecht & Patashnick Co., Franklin, MA). In the increased numbers of inflammatory cells in stabled horses.
laboratory experiment, the TEOM was equipped succes- Although levels of dust recorded in horse stables are gen-
sively with different inlets to measure the particle frac- erally much lower than those found in intensive livestock
tions PM1, PM2.5, PM10, and PM20. During the in situ production facilities, pollution with particles from the envi-
experiment, only the fraction PM10 was detected. In ronment of horse stables are correlated more highly with
the laboratory experiment, hemp and linen had the high- potential airway diseases of horses, especially chronic in-
est generation of airborne particles in all fractions. The flammations (recurrent airway obstruction, RAO) than in
lowest particle generation was detected with straw pel- other kinds of livestock. Constant exposure to an excess
lets. Results of the in situ investigation supported results of respirable dust is highly associated with chronic airway
of the laboratory experiment with respect to mean parti- diseases such as RAO.4-6 In addition, acute respiratory dis-
cle generation of straw pellets. With an average of 111.2 eases caused by infectious agents may be exacerbated and
149.2 mg/m3, it was significantly lower than the mean prolonged by permanent dust inhalation. Studies by
particle generation of wheat straw with 227.5 280.8 Vandenput et al7 reported that airway function rapidly
mg/m3. The particle generation of wood shavings had improved when dust levels in the stable were reduced.
an average of 140.9 141.9 mg/m3 and also was signif- Lower respiratory tract inflammation also results in poor
icantly lower than the generation by wheat straw. An performance in young athletic horses. Leadon8 also
activity-correlated variation of particle concentrations associated high exposure to stable particles with poor per-
was found. In conclusion, taking both experiments formance in Thoroughbred race horses.
into consideration, straw pellets seemed to be suitable In addition to gases, air in a stall has animate and inani-
for horse stables, to promote an improvement in the mate impurities. The most common animate impurities
stable climate in relation to airborne particle formation. are bacteria, yeasts, fungi, viruses, and mites, as well as pro-
tozoans. The inanimate particles are referred to as dust.
This can, however, carry with it other materials such as
From the Research Centre for Animal Production and Technology, Georg August microorganisms and endotoxins. The inanimate and
University, Goettingen, Vechta, Germany.
Reprint requests: Kathrin Fleming, Georg-August-University of Goettingen, Research animate particles appear as a combined conglomerate in
Centre for Animal Production and Technology, Universitaetsstr. 7, D-49377 Vechta, the air.9 The particles that appear in the air are distin-
Germany. guished by their surface properties, chemical composition,
0737-0806/$ - see front matter
Ó 2008 Elsevier Inc. All rights reserved. and bioresistance, but their form and size may show quite
doi:10.1016/j.jevs.2008.05.004 substantial differences. Dust may appear stretched like
408 Journal of Equine Veterinary Science Vol 28, No 7 (2008)K Fleming et al Vol 28, No 7 (2008) 409 fibers or bent, in flakes, or have a spherical or polymorphic analyzer TEOM 1400a (Rupprecht & Patashnick Co, form. The form of the particles may play a role in relation to Franklin, MA). This instrument incorporates a tapered a potential risk to health. The reason for this is that fiber- element oscillating microbalance, a micro-weighing like particles can be more damaging than spherical ones, technology that provides true mass measurements.22 The assuming that the contents are identical.10,11 TEOM 1400a consists of two components, a control The depth of penetration of the human respiratory tract unit and a sensor unit that contains the air inlet, as well has become accepted as the criterion for differentiation of as a micro-scale. This scale is made up of an oscillating particle size. The definitions are only dependent on size conical tube with a filter attached at the top. The air flows and do not take into consideration the particle composi- through this tube. The oscillation is influenced by the dust tion. In the European norm EN 481,12 the critical upper load and can be drawn on for weighing over the course of aerodynamic particle diameter (Dae) corresponding to an time. elimination efficiency for the particle collection of 50% is The particle analyzer can be equipped with diverse sam- determined. ple inlets to measure the different particle fractions PM1 Particle fractions are subdivided into (a) an inhalable frac- (fraction
410 K Fleming et al Vol 28, No 7 (2008)
Closed chamber
were measured continuously for about 4 hours starting
height = 1.5 m from the time of application. The currently measured value
width = 1 m was recorded every minute. In the laboratory experiment,
depth = 1 m the measuring heads PM1, PM2.5, PM10, and PM20 were
Sample inlet used in succession. For each bedding material, variable,
Door made
and particle fraction, three repeat measurements were
of plexiglass carried out.
In Situ Experiment. The materials wheat straw, wood
shavings, and wheat straw pellets also were investigated
under in situ conditions to determine airborne particle
generation in a horse stable. These materials were the
same batches as in the laboratory experiment. These three
Bowl with
rotating paddles
bedding materials were used for the following reasons.
Sensor unit
diameter = 0.5 m Straw is still considered to be the most frequently used
TEOM 1400a
material in horse stables and so was used as a reference
1m material. Wood shavings also are frequently used in every-
day practice and are frequently used for horses with a high
level of sensitivity to dust and allergies. Straw pellets
were selected because of very good results obtained in
laboratory experiments.
The in situ experiment was performed from January to
June in 2007 in an enclosed, roofed horse stable (9.7 m
long, 8.7 m wide, and 3.5 m high) which included five sin-
Control unit gle stalls and an aisle (Fig. 2). The stable had four windows,
TEOM 1400a which could not be opened. The two doors of the stable
were half-opened during the investigation, day and night.
The stable was naturally ventilated. Over the entire exper-
imental period, average outside air temperature was 9.9
5.68C and average relative humidity was 67.4 19.2%.
Figure 1. Outline of the closed chamber including the The TEOM 1400a was placed in the center stall of the
rotating paddles and the particle analyzer TEOM 1400a stable (represented by the concentric circles in Fig. 2).
(side view, cross section). The sample inlet PM10 of the particle analyzer was con-
structed to a height of 1.80 m. In the in situ experiment,
because of relevance for health, only the measuring head
A defined volume of each bedding material (20 liters) PM10 was used, as all particlesK Fleming et al Vol 28, No 7 (2008) 411
aisle was swept. After feeding at 6:00 PM, the aisle was swept
window window
again.
stall 1 stall 2
0.9 x 1.3 m 0.9 x 1.3 m
2.8 x 4.6 m 2.8 x 4.6 m
Microbiological Monitoring
Microbiological monitoring was carried out with all six
window
0.9 x 1.3 m
materials. Before beginning the experiment, amounts of
aisle mold and enteric bacteria, as well as the total count of
door 1 door 2
2.5 x 9.7 m aerobic mesophils in the material was determined. In the
in situ experiment at the end of a 14-day period, the
mold, enteric bacteria, and total count of aerobic meso-
window stall 3 stall 4 phils in the bedding material used was determined.
0.9 x 1.3 m N
3x3m 3x3m
Statistical Analysis
Statistical evaluation of the data was carried out with the
Tiny Tag: detection of air temperature (°C) and relative air humidity ( )
software program SAS 9.1 (SAS Inst. Inc., Cary, NC).
stable height: 3.50 m
To evaluate data records from the laboratory experiment,
TEOM 1400a particle analyzer, sample inlet PM 10, height 1.80 m
the average concentrations in the first 120 minutes of mea-
Figure 2. Outline of the stable facility showing the surement were used. Analysis of variance was computed us-
location of the stalls, the aisle, doors, and windows. ing the general linear model (GLM) procedure, taking into
account the constant parameters material, period of rota-
tion, and rotational speed. There were interactions be-
Table 1. Mass of bedding materials for each trial tween the material and period of rotation and the
replication of 14 days material and rotational speed. An interaction between
period of rotation and rotational speed was tested, but it
Bedding Material Bedding Amount on Day 1
was not significant.
Wheat straw 3.5 kg/m2 For statistical evaluation of results from the in situ exper-
Daily refilling mass ¼ 11 iment, an analysis of variance was carried out using the pro-
kg/stall cedure GLM, taking into account the fixed parameters
Straw pellets 17 kg/m2 material, repeat, activity, and day of experiment. Interac-
Wood shavings 12 kg/m2 tions were found between material and repeat, material
and activity, and material and day of experiment. The rela-
tive humidity and air temperature in the stable were taken
Also, the volume of droppings and the amount of manure into account as covariables. Data from both experiments
for disposal is greatly reduced compared, for example, with are reported as least square means (LSM) standard error
straw. (SE). The significance level was P % .05.
This method was chosen to reflect the practical ‘‘real life’’
situation, which is in many respects most relevant. With all
three materials, during one 14-day trial period, the stalls RESULTS
were not mucked out. The excrement was simply removed
Particle Size Fraction
once a day, and the bedding mattress was straightened.
Table 2 shows the particle size fractions of the six bedding
Masses of the initial bedding materials used are shown in
materials. The small particle fractions of linen and hemp
Table 1.
had the highest percentage of the initial weight. Consider-
During the trial, four horses (Oldenburg warm blood
ing the particle fractions412 K Fleming et al Vol 28, No 7 (2008)
Table 2. Mean particle size fractions of the bedding materials, n ¼ 4 repetitions/material/particle fraction
Bedding Material Initial Weight [g] >9.9 mm [g] 9.9L5 mm [g] 4.9L2 mm [g] 1.9L1 mm [g]K Fleming et al Vol 28, No 7 (2008) 413
a 7000
PM 10 c
a 450
d d Wheat straw Wood shavings
PM 20 400 b
Hemp Linen
concentration PM 1 [µg/m3]
6000
concentration [µg/m3]
c Straw pellets Paper cuttings
Airborne particle
350
5000
Airborne particle
b 300
4000 a
250
3000 b b
b e 200
a b
2000 a
150
a
1000 b b b
100
a a b
a a
0 50
a
Wheat Wood Hemp Linen Straw Paper
straw shavings pellets cuttings 0
1 5
Material
Rotation time [min]
c
b 1200
PM 1 b 450
PM 2.5
concentration [µg/m3]
1000 400 Wheat straw Wood shavings
concentration PM 1 [µg/m3]
a
d Hemp Linen
Airborne particle
350 Straw pellets Paper cuttings
800
Airborne particle
300
600
250
b
400 200
b c
a a b a
d 150 a
200
a b b a a
e 100 a
0 a a b
b
50 b
Wheat Wood Hemp Linen Straw Paper
straw shavings pellets cuttings 0
Material 14 8
Figure 4. Airborne particle concentrations (LSM SE) Speed of rotation [rpm]
of (a) PM10 and PM20 and (b) PM1 and PM2.5 within Figure 5. Airborne particle concentrations PM1 (LSM
the first 2 hours after rotation (per 1 kg material, n ¼ 72), SE) of the different materials depending on the (a)
a, b, c, d, e ¼ within one particle fraction, LSM without rotation time and (b) speed of the rotation, (n ¼ 36),
a common letter differ (P < .05). a,b ¼ within one material, LSM without a common
letter differ (P < 0.05).
sweeping) had a highly significant (P < .0001) influence on
airborne particle concentration. The day of the experiment were cleaned and strewing and sweeping the stable aisles
also had a significant (P < 0.0001) influence on concentra- took place) and in the evening from 6:00 PM (feeding,
tion of airborne particles. Likewise, the interactions bed- sweeping the stable aisle) for all materials, but especially
ding material/repetition, bedding material/activity, and with wheat straw, with a maximum value of 720.9 mg/
bedding material/day were highly significant (P < m3. In the period between 1:00 and 6:00 PM, during which
.0001). Relative air humidity, as well as air temperature time horses were not in the stalls, as well as at night
in the stable, had no significant influence, in this study, (between 11:00 PM and 5:00 AM), the values reached
on particle concentration. The influence of repetition was a low level.
not statistically significant (Table 3). Within an experimental period of 14 days, average parti-
Over the entire period of the experiment, particle cle concentrations varied in all three bedding materials, so
concentration with straw pellets was the lowest, with an av- that no trend could be established. Littering down with
erage of 111.2 149.2 mg/m3. Average particle concen- wheat straw caused a higher development of particles com-
trations for wheat straw and wood shavings were 227.5 pared with wood shavings and straw pellets. The average
280.8 mg/m3 and 140.9 141.9 mg/m3, respectively. concentration of wheat straw differed significantly, on the
In Figure 6, average particle concentrations PM10 of the first experimental day, with a value of 557.8 31.7 mg/
three bedding materials investigated in the course of an m3, from the average concentration of wood shavings
experimental day are illustrated. Clear increases were found (218.6 31.5 mg/m3) and straw pellets (185.9 38.5
in the morning from 11:00 AM (the time at which boxes mg/m3) (Fig. 7A).414 K Fleming et al Vol 28, No 7 (2008)
Table 3. Significant sources of variation in airborne Hemp and linen produce the highest amount of particles,
particle concentration PM10 and small particle fractions PM1 und PM2.5 above all.
Hemp and linen straw are produced during hemp/linen
Significance fiber preparation and are composed of the residue of lig-
Source of Variation P-Value nified plant parts (shives). A significant proportion of the
Bedding materialK Fleming et al Vol 28, No 7 (2008) 415
800
700 Wheat straw
concentration PM 10 [µg/m3]
Straw pellets
Wood shavings
Airborne particle 600
500
400
300
200
100
0
00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00
Feeding Horses out, stable Horses in, feeding,
work, sweeping sweeping
Time
Figure 6. Average particle concentrations PM10 of wheat straw, wood shavings, and straw pellets in the course of a day,
n ¼ 42, measured value/material.
a
concentration PM 10 [µg/m3]
b
concentration PM 10 [µg/m3]
700 Wheat straw 350 Wheat straw
Straw pellets Straw pellets
600 300
Wood shavings
Airborne particle
Wood shavings
Airborne particle
500 250
400 200
300 150
200 100
100 50
0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 Week 1 Week 2
Day
Figure 7. Airborne particle concentrations (LSM) of wheat straw, straw pellets, and wood shavings depending on (a)
the day of trial and (b) the trial week; n ¼ 9.
Table 4. Coefficient of variation [%] of the mean materials, the ability of shavings and straw to absorb water
particle concentrations of wheat straw, straw pellets, is markedly higher than that of cereal straw.25,26 Omitting
wood shavings within a day and between the days daily restrewing of wheat straw could, however, result in se-
vere soaking of the manure mattress. This probably would
Coefficient of Variation [%] result in reduced generation of particles but, in contrast, in-
Bedding Within Between creased generation of gas (ammonia formation) in the stall.
Material n a Day the Days The C/N ratio is an expression of amount of carbon rel-
ative to nitrogen. The C/N ratio is important because of
Wheat straw 1991 60.3 50.9
the relationship between this ratio and nitrogen absorption
Straw pellets 1960 33.2 63.5
in bedding material. Microorganisms that are involved in
Wood shavings 1993 40.9 11.4
the transformation processes need a source of carbon for
their energy requirements and nitrogen to build up nitrate
can be assumed that, with a single strewing of wheat straw, and biomass. An optimal C/N ratio for the transformation
generation of particles would also have been significantly processes ranges between 25:1 and 50:1.27 If the C/N
smaller and the peak concentration would not have ratio is too low, nitrogen is not completely incorporated
appeared at 11:00 AM. Some earlier investigations have in the biomass and is emitted as ammonia.27 Conversely,
demonstrated that, as a result of the preparation of one might suspect that, as a result of daily restrewing416 K Fleming et al Vol 28, No 7 (2008)
Table 5. Total count of microorganisms as well as enteric bacteria and mold in the different bedding materials before
the start of the experiments, as well as at the end of a research period, respectively, of 14 days for wheat straw, straw
pellets and wood shavings
Total Count of Enteric Bacteria Mold Fungi*
Microorganisms [CFU/g] [CFU/g] [CFU/g]
Material/Manure Material/Manure Material/Manure
Bedding Material Mixture Material Mixture Material Mixture
Materials n[3 n[8 n[3 n[8 n[3 n[8
Wheat straw 7.5 $ 107 8.96 $ 109 2.24 $ 105 1.24 $ 107 2.6 $ 104 8.3 $ 105
Straw pellets 2.4 $ 104 2.81 $ 109 0 8.75 $ 107 0 7.35 $ 106
Wood shavings 3.0 $ 105 3.39 $ 109 0 8.71 $ 106 0 8.75 $ 103
Hemp 1.1 $ 105 3.5 $ 105 0
Linen 6.7 $ 106 1.44 $ 106 0
Paper cuttings 1.9 $ 102 0 0
* characterized as Scopulariopsis koningii
with wood shavings and straw pellets, increased particle used in horse management were compared. The systems
concentrations would be detected in the stall. But, as investigated were straw/hay and the dust-reducing system
already mentioned, when using these bedding materials, wood shavings/silage. Here, as well, markedly lower parti-
it is not necessary to strew or restrew with the bedding cle concentrations (PM < 7 mm) were established in the
material on a daily basis. stable when wood shavings/silage were used in compari-
Contrary to our assumption, in this in situ study, relative son with straw/hay. Particle concentrations when wood
air humidity and air temperature in the stable had no effect shavings were used were, on average, 0.22 mg/m3 com-
on generation of airborne particles (Table 3). It can be pared with straw bedding, which had an average value of
assumed that with higher values of humidity, generation 1.1 mg/m3.
of particles would be reduced. It also is known from the In a similar experiment, Woods et al18 obtained compa-
literature that these factors exercise a great influence on rable results. With wood shavings bedding and pelleted
particle concentration in the stable.28 feed, there were likewise clearly lower concentrations of
In the investigation presented here, influence of activity airborne particles (K Fleming et al Vol 28, No 7 (2008) 417
were different prerequisites for stable design and size, as hygiene conditions in Bavarian horse farms. 1st Report: Stable build-
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