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S. Shanmugavelu, G. Burnett and W. MichieJ. Trop. Agric. and Fd. Sc. 28(2)(2000): 221–234

Effect of misting on the performance of male broilers in an enclosedenvironment(Kesan pengabusan terhadap prestasi ayam pedaging jantan dalam persekitarantertutup)

S. Shanmugavelu*, G. Burnett** and W. Michie***

Key words: broiler, misting, enclosed environment, evaporative cooling

AbstrakSatu ujikaji telah dijalankan untuk mengkaji kesan penyejukan sejatan terhadapprestasi ayam pedaging jantan Ross. Suhu dalam dua kumpulan rawatan telahdiubah daripada 24 °C kepada 28 °C mengikut masa. Ayam pedaging dalam satudaripada kumpulan rawatan ini telah disembur (misted) dengan air. Ayam dalamkumpulan kawalan telah berada pada suhu 21°C. Dua ujikaji telah dijalankan (1dan 2) dengan sistem kabus (misting) yang berlainan. Satu sistem kabus didapatidari pasaran yang beroperasi pada tekanan 414 kPa dan mengeluarkan kabuskasar, manakala sistem yang kedua beroperasi pada tekanan 1 380 kPa danmengeluarkan kabus yang halus. Penurunan suhu purata ialah 1.3 °C dan 1.6 °Cdengan kelembapan 71% dan 83% dalam ujikaji 1 dan 2. Pada umur 7 minggu,berat badan ayam didapati lebih tinggi pada kumpulan kawalan diikuti dengankumpulan yang dikabus dan kumpulan yang tidak dikabus. Purata pertambahanberat badan, pengambilan makanan harian dan kecekapan penukaran makananmenunjukkan trend yang sama seperti berat badan.

Kadar pengambilan air dalam kumpulan yang tidak dikabus lebih tinggi(p <0.05) dibandingkan dengan kumpulan kawalan atau kumpulan yang dikabus.Walaupun kadar kelembapan tinggi (71% and 83%) dalam kumpulan yangdikabus, aras amonia (≤5 ppm) tidak meningkat. Kumpulan kawalanmenunjukkan kadar kematian yang lebih tinggi (p <0.05) dibandingkan dengankumpulan yang lain. Kebanyakan kematian disebabkan oleh ‘ascites’. Kaedahkabus atau semburan air juga dapat mengurangkan aras habuk.

AbstractA study was done to evaluate the effect of evaporative cooling on theperformance of Ross male broilers. The temperature in the treatment groups wasfluctuated with time of day from 24 °C to 28 °C. Birds in one of the treatmentgroups were evaporatively cooled by misting. The control group was maintainedat 21 °C. Two experiments (1 and 2) were conducted with two different sets ofmisting equipment. The first with a misting system available commercially,operating at 414 kPa to generate a coarse mist and the second custom designedwith oil-jet nozzles operating at about 1 380 kPa that create a fine mist. Themean temperature drop achieved with misting was 1.3 °C and 1.6 °C while the

*Livestock Research Centre, MARDI Headquarters, P.O. Box 12301, 50774 Kuala Lumpur, Malaysia**Centre for Rural Building Research, Craibstone, Bucksburn, Aberdeen, United Kingdom***Poultry Department, Scottish Agricultural College, Craibstone, Aberdeen, United KingdomAuthors’ full names: Shanmugavelu Sithambaram, George Burnett and Walter Michie©Malaysian Agricultural Research and Development Institute 2001

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relative humidity was 71% and 83% in experiment 1 and 2 respectively. Therewas no difference between the non-misted and misted groups at week 4 and 6 butboth were significantly (p <0.05) heavier than the control group at 3 weeks ofage. At 7 weeks, however all three groups were significantly different with theheaviest bird in the control group and the lightest bird in the non-misted group. Asimilar trend was observed with average daily gain, average daily feed intake andfeed conversion ratio with the control ranking the highest and non-cooled thelowest.

The mean water intake (both experiments) of the birds in the non-mistedgroup was significantly (p <0.05) higher than the misted or the control, especiallyafter 35 days of age. The pattern of water to feed intake ratio was similar to thoseof water intake. Despite a high relative humidity (71% and 83%) in the mistedgroup, there was no increase in the ammonia level (≤5 ppm) or the degree ofhock burn. The control group had a significantly (p <0.05) higher cumulativemortality rate (18.6%), compared to either the misted (12.9%) or the non-mistedgroup (12.4%) at 49 days of age. The main cause of death was ascites, which isassociated with increased growth rate. The dust levels were also reduced (53%)with misting.

IntroductionThe effects of temperature and humidity onbroilers have been well established (Princeet al. 1961; Adams et al. 1962; Deaton et al.1978; Charles 1986; Howlider and Rose1987). A balance between heat loss and gainmaintains body temperature. At hightemperatures, the main mode of heat loss isin the form of latent heat while at lowtemperatures it is sensible. At hightemperature, the birds reduce feed intake inan attempt to reduce heat load and maintainbody temperature. This reduction in feedintake is detrimental to production.Nutritional manipulations and environmentalmodifications have been attempted to reduceheat load. One such method is misting orfogging with water in an attempt to reduceheat load and improve performance.

Misting or fogging is a process ofevaporative cooling in which the sensibleheat in the air is used to evaporate water putin contact with it. This results in a reductionin air temperature and a rise in latent heat orhumidity (Timmons and Baughman 1983;Simmons and Deaton 1989). The efficiencyat which the evaporative process takes placeis influenced by the contact time betweenthe air and water droplet (Timmons et al.

1981; Timmons and Baughman 1983;Scarborough et al. 1988).

It is therefore strongly influenced bythe ventilation rate (Gates et al. 1991) andthe size of water droplet in the air (Timmonset al. 1981). If the ventilation rate is high,the contact time between the air and waterwould be reduced and thus the temperaturedrop would not be great. This could havebeen the reason for the failure to obtainsignificant results with misting in open typehousing system (Shanmugavelu 1995, 1996)where there was insufficient contact timebetween the air and water droplet.

The other question that frequentlyarises is that the high humidity conditions(80–90%) generated by evaporative coolingmay hinder heat transfer. This is becauseevaporative heat loss via the respiratory tractfor broilers accounts for more than 80% ofthe total heat produced at highenvironmental temperatures (Richards 1976;Farrell and Swain 1977a, b). The presenceof a vapour pressure gradient is thereforeessential for heat transfer at hightemperatures. Nevertheless, evaporativecooling has also been observed to bebeneficial in high humidity areas (Reece andDeaton 1971).

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S. Shanmugavelu, G. Burnett and W. Michie

With these questions in mind, a studywas conducted to evaluate the effect ofmisting of male broilers in an enclosedenvironment. Enclosed environment waschosen for two reasons: 1) the increaseinterest in such housing systems in Malaysiaand 2) better control of ventilation anddirection of air flow for misting.

Male broilers were chosen as theywould be more susceptible to heat stressthan females due to a higher body weight atany given age. The experiment wasconducted in a research facility at theScottish Agricultural College in Craibstone,Aberdeen, United Kingdom.

Materials and methodsDescription of treatment groupsTwo separate experiments were carried out,one with coarse misting and the other withfine misting or fogging. In each experiment,a total of 1 428 Ross male broilers (onarrival, Day 0), were divided into twogroups, weighed in groups and brooded intwo separate rooms on 0.1 m woodshavings. Whole house brooding with fourspot brooders was started at 32 °C with thebackground at about 3 °C lower. Thetemperature was reduced by 0.5 °C per dayup to day 14 when it was 25 °C. Ventilationwas adjusted according to need by openingthe inlet and outlet flaps controlled by 24Vac linear actuators.

On day 14, 212 birds were allocated tosix rooms (two rooms per treatment) withtwo pens each, making a total of 106 birdsper pen (Figure 1a and 1b). Wood shavingsat a depth of about 0.1 m were spread on theconcrete floor. Birds were acclimatised fromday 14 to 20. During this period, thetemperature in the control room was reducedby 0.5 °C per day while that in the non-misted and misted rooms were increased by0.5 °C per day. On day 20, the temperaturein the control room was 22 °C while that ofthe treatment was 28 °C.

From day 21 to 49, the control roomwas targeted for a constant 21 °C, while thetemperature in the non-misted and misted

rooms fluctuated with time of day. Theheating was increased to 29 °C at 0600 hand reduced to 24 °C at 1500 h. The heatercontrols that operate the non-misted roomswere used to control the misted rooms toensure that each pair of rooms receivedsimilar heat input. Between 1000 h and1500 h, the misted group was misted withwater. All temperature settings were pre-calibrated.

Description of treatment roomsEach room measured 9.25 x 4.45 x 2.5 m.Within this space, two pens measuring3 x 3 m were used. The partitions of the penwere of hard board at a height of 0.5 mfollowed by 1.2-m wire netting, with twosliding doors. The floor space for 106 birdsper pen was 0.08 m2/bird (12.4 birds/m2).The rooms had suspended ceilings of 50 mmclosed cell polystyrene. Tube heaters locatedat the ceiling with the control unit outsideeach room heated all rooms. Ventilationprovided was based on feed intake andmaintained at a minimum of 2 m3/s pertonne feed per day. A plan of theexperimental facility is shown in Figure 1aand 1b.

Misting equipmentIn the first experiment, a commerciallyavailable mister with an atomising nozzlewas used with one nozzle per pen located inthe middle of the pen at 2.5 m above thefloor (Figure 1a). A scroll and stator pump(Mono-M, Type CMS/221, operating at 414+ 35 kPa) supplied water to the mister. A 24VAC minute timer was used to turn themister on and off, as its timer was notreliable. The pressure build up in the hose,when the mister was turned off, resulted inthe release of coarse water droplets. Thesewere collected in a 0.7 x 0.5 x 0.005 m traylocated 2 m above the floor and 0.5 mbelow the mister nozzle (Figure 1a).

In the second experiment, oil-jetnozzles (Danfoss, 80 degrees spray anglerated at 2.84 L/h) attached to 15 mm coppertubes were connected to a high-pressure

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washer (K.E.W. Hobby, Model 80–1)operating at 1380 kPa. Three nozzles werespaced evenly per misted group (Figure 1b).A 24 VAC minute timer was used as aswitch. An estimate of the amount of waterthat can be added by misting was calculatedbased on ventilation rate and bird moistureproduction (CIGR 1984) and externalweather data collected 2 weeks prior tomisting.

FeedBirds were fed commercial starter crumbsfor 2 weeks, grower pellets on the thirdweek and finisher pellets from 4 to 7 weeks.Feed and water were provided ad libitum.The composition of the feeds is shown inTable 1.

Data collectionTemperature Temperature measurementswere made with thermocouples (Type T)connected to a data logger (Sinclair 21X,Campbell Scientific, UK). The temperaturewas measured at 20-second intervals and themean recorded every quarter hour. Allsensors were located about 0.6 m above thefloor in the middle of each room. Wet anddry bulb temperatures of both theexperimental units and the ambient wererecorded with aspirated psychrometer(Rosemount Model No. E 13423). Allsensors were connected to the data logger.

All temperature readings were checked dailywith a sling psychrometer (Casella, London)and data was downloaded weekly with alaptop computer. It was ensured that thesensors were free from direct wetting in themisted rooms. Relative humidity (RH) wascomputed from wet and dry bulb readings(CIBSE Guide 1986).

Water intake In the first experiment(Figure 1a), water consumption wasmeasured using water tanks (25 L) located1.4 m above the floor in the middle of eachpen and in the second (Figure 1b) with200 L water tanks located outside eachroom. Average daily water intake wascomputed as mL/bird per hour based on thebalance of birds on that day.

Dust levels Dust level was measured withCasella dust pumps (Model T 13160/1,Casella London) attached to Casella totaldust sampling heads (Model T 13087).Whatman GF/A 2.5 cm glass microfibrefilters, which retain all particles larger than1.6 microns was used to trap dust. Thesampling head was located 0.4 m above thefloor in the middle of the first pen in eachroom. Empty filter papers were kept in adesiccator for at least 24 hours beforeweighing. Separate dust measurements weremade for the 5-hour misting period and theremaining non-misting periods.Measurements only began after each daily

Table 1. Composition of feeds

Component Starter crumbs Grower pellets Finisher pellets(0–2 weeks) (3rd week) (4–7 weeks)

ME (MJ/kg) 12.3 12.7 13.0Protein (%) 23.0 22.0 20.0Fibre (%) 2.5 2.5 2.5Oil (%) 5.5 7.0 7.0Ash (%) 6.0 6.0 6.0Vit A (iu/kg) 12 000 12 000 12 000Vit D (iu/kg) 4 000 4 000 4 000Vit E (iu/kg) 25 000 40 30CuSO4 (mg/kg) 25.0 25.0 25.0Maduramicin ammonium (mg/kg) 5.0 5.0 –Narasin (mg/kg) – – 70.0Virginiamycin (mg/kg) 20.0 20.0 10.0

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routine (cleaning, feeding etc) to avoid falsedust values. The flow rate was calibrated to2 L/min at the start and measured at the endwith a flow meter. The mean flow rate andthe period of run were recorded. Thedifference between the weight of the filterpaper with and without dust wastransformed to read dust levels as mg/m3.

Ammonia Ammonia levels weremonitored at bird level with Drager tubes(CH 20501) attached to a Drager GasDetector Pump (Model 31). Initial readingswere low (<5 ppm) and thus subsequentmeasurements were only made when it wasdetectable by smell (about 10 ppm). Whenammonia was detected by smell, theventilation rate was re-checked, using a hotwire anemometer (E.T.A 3000) and avaneometer (Dwyer Instruments, USA) torule out inadequate ventilation.

Litter moisture content Wood shavingswere added according to need. To avoiderrors in dust measurements, all roomsreceived wood shavings even if it wasnecessary only for one room. Litter sampleswere collected before addition of woodshavings. Samples were taken at 10locations in each pen and pooled, torepresent the whole pen. At each location, acomplete core sample of litter was taken.The samples were weighed immediatelyafter collection and frozen. Frozen sampleswere dried in an oven at 105 °C for 48 hand weighed to determine moisture content.

Measurement of feed intake and weightgain All birds were weighed weekly andfeed intake assessed weekly. All dead birdswere removed once a day (morning) andweighed. Average daily gain, average dailyfeed intake and feed conversion ratios werecomputed. Feed conversion ratio (FCR) wascalculated as total intake divided by the totalweight gain for the week. The total gainincluded the estimated weight gain of deadbirds.

Statistical analysis Analysis of variancewas done to test the difference between thethree treatment groups and interactionbetween experiments (Minitab 1989).Significant differences between means weretested with Duncan multiple range test(Bruning and Kintz 1977). Chi-square testswere done to detect differences in mortalitybetween groups. As there was no differencebetween experiments, data was pooledexcept for temperature and relative humidity,which were reported separately to show theeffect of different types of misting systems.

Results and discussionTemperature and humidityThe mean air temperature drop obtainedwith misting was 1.3 °C and 1.6 °C withcoarse and fine misting respectively(Figure 2). The ambient temperature drop, asexpected, was higher with finer waterparticles in the high-pressure system (1 380kPa) as they remaining longer in air andtherefore increased the potential forevaporation. The RH on the other hand didnot exceed 85% (Figure 3) even with highpressure misting. It was possible that themaximum moisture holding capacity for theventilation rate had been reached or themisted water was not evenly distributedthroughout the pen.

The calculated evaporative efficiencywas 30.4% for the coarse misting (414 kPa)and 44.6% for the fine misting (1 380 kPa)systems similar to those reported byTimmons et al. (1981) who obtained a15–25% efficiency with low pressuresystems and up to 50% with high pressureones. Timmons and Baughman (1983) alsoobtained an increase in saturationeffectiveness of 14% (23% to 37%) byincreasing line pressure from 275 kPa to1 380 kPa. The difference in efficiencybetween the high (1 380 kPa) and low (414kPa) pressure misting system in the presentexperiment was also 14% (44.6% minus30.4%). In contrast, evaporative pad systemshave efficiencies that exceed 75% (Timmonset al. 1981).

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The coarser water droplet emitted bythe low-pressure system that did notvaporise fell on the bird and the litter. Thelitter, however, dried up considerably thefollowing day and so there was no obviousdifference in the litter moisture content.Besides visual observation of mild litterwetting immediately following misting,there was a constant RH difference of 10%between the non-misted and misted group inthe coarse misting system compared to onlya 5% difference in the fine misting system.This indicates less vaporisation with lowpressure misting and more water on thefloor with a resultant high RH maintainedthroughout the day as observed byScarborough et al. (1988). The benefit ofcooling with minimal temperature dropaccompanied by low pressure systems wasattributed mainly to surface wetting of thebird with eventual evaporation from heatsupplied by the bird (Timmons andBaughman 1983; Gates et al. 1991).

In the present study, the surfaces of thebirds were observed to be wet with water inboth the experiments. In fact, the birds werealso observed to move towards the source ofwater falling on the litter when the mistingwas initially turned on. A small number ofbirds in both the non-misted and mistedgroups were observed to burrow and covertheir body with litter. This was probably tocool their body through contact with wet ormoist litter, where the litter can get moisteither from misting or faeces.

Bird performanceThere was no difference between the non-misted and misted groups at week 4 and 6but both were significantly heavier than thecontrol group at 3 weeks of age. At 7 weeks,however, all the three groups weresignificantly different (Table 2) in weightwith the heaviest birds observed in thecontrol group and the lightest birds in thenon-misted group.

It is apparent that the birds in thecontrol group were significantly heavier thanbirds from both treatment groups. This was

expected as it was reared at the optimaltemperature of about 21 °C. The beneficialeffect of misting was evident after 6 weeksof age when the birds were heavier andproduced more heat. Body weight andaverage daily gain (Table 2) weresignificantly higher in the misted group at 7weeks compared to the non-misted group. Inaddition, the average daily feed intake(Table 2) of the misted group was notdifferent from the non-misted group at 7weeks, indicating that it could put on moreweight without a significant increase in feedintake. This can be observed from Table 2where feed conversion was not significantlydifferent between the control and mistedgroups but both were significantly betterthan the non-misted group.

Another indicator of heat stress iswater intake. The increase in intake with agewas 6 mL/bird per hour at 3 weeks to about16 mL/bird per hour at 7 weeks (Table 2). Itwas observed that the birds in the non-misted group started consuming more waterthan food after 5 weeks of age (Table 2)indicating a heat stress condition (Wilson etal. 1957). The misted group, however,consumed water similar to the control groupand therefore, misting appears to relieveheat stress.

Dust concentrationDust levels in an enclosed house are of greatconcern for health where the humanthreshold level is 10 mg/m3 (Carpenter1986). The dust levels were numericallyreduced during the period of misting andnon-misting in both the misted and controlgroups compared to the non-misted group(Table 3).

The dust level in the misted group wasslightly higher than the control probably dueto the higher environmental temperature.Nevertheless, it appears that there was atrend of a lower dust level with misting. Itshould also be noted that the measured dustconcentration values were within the rangeof values measured in experimental units byWillis et al. (1987) for 80 birds/pen.

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Table 2. Bird performance

Age (weeks) Non-misted Misted Control Std error on mean

Mean body weight (g)2 435.0 434.5 432.6 8.853 868.5 870.6 854.2 6.714 1 431.9a 1 419.3a 1 397.2b 9.125 1 979.6 1 967.1 1 987.4 13.866 2 488.6a 2 523.2a 2 605.0b 22.667 2 897.9a 3 011.0b 3 178.2c 26.60

Average daily gain (g)3 61.92 62.30 60.22 0.764 80.50 78.38 77.58 1.085 78.23a 78.26a 84.31b 1.676 72.72a 79.45a 88.24b 2.467 57.34a 70.17b 82.10c 2.53

Average daily feed intake (g)3 94.35 93.09 94.89 0.784 134.07 132.58 131.81 1.035 162.18a 160.21a 165.84b 1.236 173.33a 177.66a 187.14b 1.767 178.76a 185.76a 199.33b 2.57

Feed conversion ratio3 1.52 1.49 1.58 0.02664 1.67 1.69 1.70 0.02305 2.08 2.06 1.99 0.03476 2.43 2.29 2.17 0.07187 3.24a 2.74b 2.56b 0.10442 to 7 2.13a 2.05b 2.04b 0.0183

Mean water intake (mL/bird.hour)3 7.25 7.32 7.18 0.174 9.80a 9.97a 9.10b 0.185 12.84a 12.44a 11.20b 0.226 15.04a 13.77b 13.31c 0.167 15.84a 14.39b 14.90b 0.21

Water to feed intake ratio3 1.80 1.85 1.77 0.03254 1.82 1.88 1.72 0.07525 1.90a 1.86a 1.62b 0.04186 2.08a 1.86b 1.71b 0.04917 2.13a 1.86b 1.80b 0.0425

abc = different letters within the same row are significantly different (p <0.05)

Hock burn and ammonia levelsIf the litter were wet or moist, it would leadto increased ammonia levels and thereforehock burns. There was no differencebetween the three treatment groups in thedegree of hock burn. Misting did not resultin increased ammonia level, as the overallmean ammonia level measured in all the

three groups was only between 3.0 ppm and5.0 ppm.

Litter moisture contentTo keep the litter dry, wood shavings wereadded occasionally. The amount of woodshavings used as litter material wasmeasured as number of bales (32-kg weight)

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used per treatment group to observe if therewas an additional need for the mistinggroup. Each treatment group used a total of1 bale in the first experiment and 2 bales inthe second.

Litter moisture (Table 4) wassignificantly higher for the misted groupafter 5 weeks. The litter moisture levels inall the three groups were higher than thesuggested level of about 30% for ammoniacontrol (Longhouse et al. 1968; Reece andLott 1984; Carr et al. 1990). However, themeasured ammonia levels were less than 3 ±2 ppm, which was within the acceptablelevel (Longhouse et al. 1968). It appearsthat, misting did not result in wet litter. Inthe low pressure misting system, a wettedperimeter of 1 m diameter was observed tobe visually wet at the end of misting. Thisarea, however, dried up considerably on thefollowing day.

MortalityThe total number of dead was analysed byChi-square to detect mortality ratedifferences between treatment groups. Thecumulative mortality rate (Table 5) wassignificantly higher in the control comparedto the non-misted or the misted group after 5weeks. The reason for the high number ofdeaths in this group was due to increasedgrowth rate. In fact, the birds in this group(control) were observed to be 24% heavierat 7 weeks compared to recommended bodyweight (Cobb 1987). The main cause ofdeath in all the three groups was ascites.

ConclusionThe performance of broilers raised at highenvironmental temperatures can beimproved with misting. Misting does notadversely affect the litter condition and thebuild up of ammonia was within acceptablelevels. High dust levels associated withenclosed housing systems could also bereduced with misting. The question of

Table 3. Mean weekly dust concentration (mg/m3)

Age (weeks) Non-misted Misted Control

Period of misting4 6.32 3.49 2.485 5.73 2.96 1.736 6.41 2.87 1.887 7.72 2.87 2.483 to 7 6.48 3.04 2.10

Period of non-misting4 5.08 3.19 2.525 4.34 2.76 2.016 5.14 3.44 2.107 6.85 4.19 3.043 to 7 5.31 3.38 2.39

Table 4. Litter moisture content (%)

Age (weeks) Non-misted Misted Control Std error on mean

3 43.31 42.01 47.87 3.104 49.63 50.81 53.05 2.775 46.99 53.82 52.00 2.436 38.38a 50.41b 47.50b 2.397 37.56a 49.52b 41.23a 1.48

ab = different letters within the same row are significantly different (p <0.05)

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whether or not the improvement inperformance was due to the mistedenvironmental conditions; water dropletslanding on the birds’ surface or acombination of both cannot be answeredwith the present experiment. This aspectneeds further experimental investigation.

ReferencesAdams, R. L., Andrews, F. N., Gardiner, E. E.,

Fontaine, W. E. and Carrick, C. W. (1962).The effects of environmental temperature onthe growth and nutritional requirements of thechick. Poultry Science 41: 588–94

Bruning, J. L. and Kintz, B. L. (1977).Computational Handbook of Statistics.Illinois: Scott, Foresman and Company,

Carpenter, G. A. (1986). Dust in livestock buildings– Review of some aspects. J. Agric. Engng.Res. 33: 227–41

Carr, L. E., Wheaton, F. W. and Douglas, L. W.(1990). Empirical models to determineammonia concentrations from a broilerchicken. Trans. ASAE 33(1): 260–5

Charles, D. R. (1986). Temperature for broilers.Worlds Poultry Science Journal Vol. 42(3):249–58

CIBSE Guide (1986). The Chartered Institution ofBuilding services Engineers, London. VolumeC, Section C1, p. C1–C4

CIGR (1984). Report of working group onclimatization of animal houses. p. 63–72.Craibstone, Bucksburn, Aberdeen, ScottishFarm Building Investigation Unit

COBB (1987). Cobb 500 Broiler ManagementBrochure. Essex, United Kingdom: The CobbBreeding Company Ltd.

Deaton, J. W., Reece, F. N. and Mcnaughton(1978). The effect of temperature during thegrowing period on broiler performance.Poultry Science 57: 1070–4

Farrel, D. J. and Swain, S. (1977a). Effects oftemperature treatments on the heat production

Table 5. Cumulative mortality rate (%)

Age (weeks) Non-misted Misted Control

3 0.59 1.53 0.594 3.18 3.66 3.185 6.49 6.72 8.266 9.91a 10.02a 13.92b7 12.38a 12.85a 18.63b

ab = different letters within the same row aresignificantly different (p <0.05)

of starved chickens. British Poultry Science18: 725–34

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