effect of utilizing evaporative cooling in tiestall dairy barns equipped ...

This is not a peer-reviewed article.Pp. 312-319 in Fifth International Dairy Housing Proceedings of the 29-31 January 2003Conference (Fort Worth, Texas USA) Publication Date 29 January 2003.ASAE Publication Number 701P0203, ed. Kevin JanniEFFECT OF UTILIZING EVAPORATIVE COOLING IN TIESTALL DAIRYBARNS EQUIPPED WITH TUNNEL VENTILATION ON RESPIRATIONRATES AND BODY TEMPERATURE OF LACTATING DAIRY CATTLEM.J. Brouk 1 , J.F. Smith 2 and J.P. Harner, III 3ABSTRACTDuring the summer of 2001, six tie-stall dairy barns in northeast Missouri were monitored todetermine the effects of evaporative cooling on the environment, respiration rate and bodytemperature of lactating dairy cattle housed in barns equipped with tunnel ventilation.Temperature and relative humidity were continuously monitored and recorded every 15 minutes insix barns (3 with and 3 without evaporative cooling systems) for a three-month period.Temperature and relative humidity data were averaged by hour prior to statistical analysis.Respiration rate, infrared skin temperature and rectal body temperature of 20 animals per barn (10primiparous and 10 multiparious) were measured on three different days during summer heatstress. Measurements were simultaneously taken between 7-8 am, 4-5 pm and 10-11 pm on eachof the three days. Cattle housed in evaporative cooled tunnel ventilated barns had lower (P

non-evaporative methods and 75% is lost via moisture evaporation from the skin and the lungs. Astemperature continues to increase above 27 °F, a greater percentage of heat is lost via the skin andlungs and a much smaller portion through non-evaporative methods (Kibler, 1950).When choosing heat abatement measures, it is important to remember these concepts. There aretwo general approaches to cooling dairy cattle. One must either modify the environment toprevent heat stress or implement methods that increase heat dissipation from the skin of cattle. Airconditioning is the ultimate method to modify a warm environment. It reduces air temperature andrelative humidity lowering the THI of the environment below thermally stressful levels. On acommercial basis, this is not an economical choice for modifying the environment of dairy cattle.A more economical method to reduce air temperature is by evaporative cooling. When waterevaporates it absorbs heat, reducing the air temperature. When water evaporates it also increasesthe relative humidity due to the increased level of water vapor present.Tunnel ventilation combined with evaporative cooling systems has been used in swine and poultryoperations for many years to cool the environment. Recently, these systems have been installed insome Midwest dairy facilities. It has been reported (Huhnke et al., 2001) that evaporative coolingcan reduce the number of hours at higher temperature-humidity index (THI) levels in someenvironments. Evaporative cooling is used very successfully to cool dairy cattle in hot aridclimates. Under arid conditions and high environmental temperatures, there is a great potential toreduce the air temperature and THI (Figures 1 and 2) by evaporation. However, as relativehumidity increases and or air temperature decreases, the potential of evaporative cooling to modifythe environment decreases. Data presented in Figures 1 and 2 are based on a 100% evaporativeefficiency and bring air to 90% relative humidity. The efficiency of evaporative coolingequipment ranges between 50 and 80%, which reduces the effect of the systems. In the Midwest,high relative humidity reduces the potential of evaporative cooling. As relative humidity increasesabove 70%, the potential reduction in THI is less than 10%. Data collected from dairy facilitieslocated in Kansas and Nebraska (Table 1) showed a slight reduction in the percentage of hoursabove a THI of 75 (Brouk, et al., 1999). Data from 2000 were collected utilizing similarprocedures to the 1999 data. This may have been due to ineffective design, ambient conditions ora combination of bothVery few studies reported in the literature describe the effects of evaporative cooling on the stresslevel of dairy cattle housed in humid environments. Brown et al., (1974) evaluated the effects ofevaporative cooling in tie stall housing at Mississippi State University during the summers of1970, 1971 and 1972. Milk production was significantly increased in one of the three summersand respiration rates were significantly lowered in two of three summers by evaporative cooling ascompared to the controls. The study showed that evaporative cooling could reduce peak daytimetemperatures however the authors questioned the long term benefits of the system.MATERIALS AND METHODSDuring the summer of 2001 six tunnel ventilated tie stall barns in northeastern Missouri andsoutheastern Iowa were evaluated. Three of the barns were equipped with cellulose evaporativepads and three were not. Temperature and relative humidity were recorded continuously for 11weeks from July 1 to September 15, 2001 using data loggers( HOBO® H8 Pro RH/TemperatureLogger, OnSet Computer Corp. Bourne, MA) On three consecutive days under stress conditions,respiration rates, rectal temperature, and skin temperature of three sites were evaluated on 20 cowsin each barn. Skin temperature of the rear udder, shoulder at the base of the ear was measuredusing a infrared temperature gun (Raytek® Raynger® MX model RayMX4KM98, Santa Cruz,CA). Evaporative cooling was only utilized from approximately 10:00 am until 9:00 pm in thebarns equipped with evaporative pads. Respiration and temperature data were averaged by day,time and barn prior to analysis. Data were then subjected to a replicated design analysis.1

RESULTS AND DISCUSSIONCattle housed in tie stall barns equipped with evaporative cooling had lower average respirationrates (65.7 vs 70.3 breaths/min) than those housed in barns without evaporative cooling (Table 2).However, rates observed in the morning and at night were not different, only the afternoon ratesdiffered significantly. Average rectal temperatures were also lower for the cows housed inevaporative cooled barns. Similar to respiration rates, the greatest differences existed during theafternoon. Skin temperatures followed respiration rates and rectal temperatures and weresignificantly lower for the cattle housed in the barns equipped with evaporative cooling with thegreatest differences observed during the afternoon.Changes in barn environment for evaporative cooled and tunnel ventilated barns are shown inFigures 3, 4 and 5. Greatest changes from ambient conditions are noted during the 1:00 pm to 8:00pm period. During this period temperature decreases up to 4.6ºC, relative humidity increases up to30% and THI decreases up to 3.25 units as compared to the ambient conditions. There isconsiderable variation in the response over the 11 wk trial. During the period from 9:00 pm to4:00 am and the period from 5:00 am to 12:00 pm, the evaporative pads were not utilized due tothe ambient humidity level reaching about 85%. Thus the systems had little effect upon the barnenvironment during these periods.As compared to the barns with only tunnel ventilation, barns with evaporative cooling had agreater percentage of July and August hours at a THI level below 70 and eliminated the hours inthe 85-90 THI category (Figure 6) during the hours of 1:00 pm and 8:00 pm. Evaporative coolingreduced the heat stress during the afternoon hours without increasing the stress during the eveningand night hours as compared to the tunnel ventilated barns. This study showed significantadvantages for the evaporative cooled and tunnel ventilated barns in terms of respiration rates,rectal temperatures and barn environment.Can evaporative cooling be utilized in combination with tunnel ventilation to reduce heat stress ofdairy cattle housed in the Midwest? It depends upon several factors. First, what is the ambient orenvironmental air temperature and evaporation potential? In many locations, the afternoon relativehumidity may be too great to take advantage of evaporative cooling. In the 2001 study area,nighttime relative humidity level was near the saturation point, limiting the system’s evaporationpotential. However, afternoon relative humidity levels dropped enough to have sufficientevaporation potential to make the systems effective reducing severe heat stress. In hot aridconditions, the system would work well. However, in high humidity locations its effectivenesswould be limited because the evaporation potential would be decreased.If the environment has sufficient evaporation potential, one should then consider barn design. Thebarns studied in 2001 were well designed and had a small cross-sectional area. This allowed forhigh levels of air exchanged with minimal fan horsepower. These barns were also less than 91m inlength and approximately 12 m wide with ceiling heights of less than 3 m. All barns also hadsufficient evaporative cooling pad area. These systems were utilized during the afternoon hoursand were shut down during the high humidity evening and night hours. The net effect was areduction in animal stress as compared to tunnel ventilation only. When sound design criteria arenot followed, problems arise as was noted in the 1999 study. Based on the 2000 data, there may besome advantages of the evaporative system in smaller barns as compared to large freestall barns.Smaller barns (tie stall) have a much smaller cross-sectional area than a large freestall barn. If onebuilds a barn with 3.7 m side-walls and a 4/12 roof pitch, over 25% of the cross-sectional area isthe rafter area. One approach is to utilize a ceiling or false ceiling along underside of the rafters toreduce the cross-sectional area that is tunnel ventilated and evaporative cooled. It would also bepossible to lower the sidewall height and roof pitch, which would require that the structure alwaysbe mechanically ventilated. This approach has been taken in the swine industry. Trying to mixnatural and mechanical ventilation systems has had limited success in the swine industry and thesame is likely in the dairy industry. To work effectively, evaporative cooling and tunnel2

ventilation systems must be correctly designed. Suggested guidelines to tunnel ventilation havebeen made by Tyson et al., (1998).The third thing to consider is the effectiveness of evaporative cooling with other heat abatementmethods. Work at KSU has shown the effectiveness of soaking cattle and then evaporating thewater from skin. This has been shown to be highly effective in reducing respiration rates and skintemperatures. However, to date no study has evaluated in a head-to-head comparison the effect ofevaporative cooling verses soaking and evaporation from the skin surface. It would be moreefficient to dissipate heat from the skin via evaporation rather than exchange via convection.However additional research is needed to determine the effects of tunnel and evaporative coolingsystems on milk production as compared to conventional methods of cow cooling.CONCLUSIONSEvaporative cooling in conjunction with tunnel ventilation reduced afternoon heat stress of dairycattle housed in tie-stall barns as compared to tunnel ventilation alone. Cattle housed in barnswith evaporative cooling had lower (P

2520Decrease inTemperature, o C1510543.337.832.226.721.1010 20 30 40 50 60 70 80Relative Humidity, %Figure 1. Potential change in air temperature due to evaporative cooling at various levels of ambienttemperature and relative humidity.45403530THI Change25201510543.337.832.226.721.1010 20 30 40 50 60 70 80Relative Humidity, %Figure 2. Potential Temperature-humidity index change due to evaporative cooling at various levels of ambientair temperature and relative humidity.5

TemperatureDifference, O C (Barn -Ambient)210-1-2-3-4-51 2 3 4 5 6 7 8 9 10 11Week of StudyPeriod 1 ( 9 pm - 4 am )Period 2 ( 5 am - 12 pm )Period 3 ( 1 pm - 8 pm )Figure 3. Effect of evaporative cooling on temperature difference (barn-ambient during three different periodof the day in ties-tall barns during the summer of 2001.Relative HumidityDifference(Barn - Ambient)35302520151050-51 2 3 4 5 6 7 8 9 10 11Week of StudyPeriod 1 ( 9 pm - 4 am )Period 2 ( 5 am - 12 pm )Period 3 ( 1 pm - 8 pm )Figure 4. Effect of evaporative cooling on relative humidity difference (barn-ambient) during three differentperiods of the day in tie-stall barns during the summer of 2001.6

THI Difference(Barn - Ambient)3210-1-2-3-41 2 3 4 5 6 7 8 9 10 11Week of StudyPeriod 1 ( 9 pm - 4 am )Period 2 ( 5 am - 12 pm )Period 3 ( 1 pm - 8 pm )Figure 5. Effect of evaporative cooling on temperature-humidity index difference (barn-ambient) during threedifferent periods of the day in tie-stall barn during the summer of 2001.4035% of TotalHours30252015105