Int J Biometeorol (2004) 48:213–217DOI 10.1007/s00484-003-0196-9

O R I G I N A L A R T I C L E

Silvia E. Valtorta · Miriam R. Gallardo

Evaporative cooling for Holstein dairy cows under grazing conditions

Received: 5 March 2003 / Revised: 8 October 2003 / Accepted: 8 October 2003 / Published online: 25 November 2003� ISB 2003

Abstract Twenty-four grazing Holstein cows in mid andlate lactation were randomly assigned to two treatmentgroups: control and cooled. The trial was performed at theExperimental Dairy Unit, Rafaela Agricultural Experi-mental Station (INTA), Argentina. The objective was toevaluate the effects of sprinkler and fan cooling beforemilkings on milk production and composition. The effectsof the cooling system on rectal temperature and respira-tion rate were also evaluated. Cooled cows showed highermilk production (1.04 l cow–1 day–1). The concentrationand yield of milk fat and protein increased in response tocooling treatment. The cooling system also reduced rectaltemperature and respiration rate. No effects were ob-served on body condition. It was concluded that evapo-rative cooling, which is efficient for housed animals, isalso appropriate to improve yields and animal well-beingunder grazing systems. These results are impressive sincethe cooling system was utilized only before milkings, in asystem where environmental control is very difficult toachieve. This trial was performed during a mild summer.The results would probably be magnified during hotterweather.

Keywords Evaporative cooling system · Grazing dairycows · Heat stress

Introduction

Holstein cows are sensitive to heat stress. Environmentalconditions such as temperature and humidity are interre-lated, and the combined effects must be considered whendetermining effects on feed intake and milk yield (Holteret al. 1996, 1997).

Most data about heat stress in dairy cows have beenproduced under controlled systems. However, responsesto meteorological variables have also been found ingrazing systems where the environment is not as easy tocontrol (Davison et al. 1988; Valtorta et al. 1996).

Effects of weather conditions on feed intake and milkproduction are mostly mediated by changes in core bodytemperature (West 1999), which could be affected bymanagement practices.

Under controlled housing systems, responses to hotweather are minimized when environmental strategies toreduce heat stress are introduced (Beede and Collier 1986;Bucklin et al. 1991).

Under grazing conditions, shade has been proved toalleviate heat stress during the summer months inAustralia (Davison et al. 1988) as well as in Argentina(Valtorta et al. 1996, 1997a). Additional benefits fromcombinations of sprinklers and fans may be achieved inhot or hot and humid climates (West 1999). A study wastherefore performed to evaluate the effects of sprinklingand fan cooling in a grazing system. The responses ofrectal temperature, respiration rate, milk production andcomposition to cooling before milkings were evaluated.

Materials and methods

Location and period

The trial was carried out at the Experimental Dairy Unit, RafaelaAgricultural Experimental Station (INTA), 31�110S, from 14January to 8 March 2002.

S. E. Valtorta ())Researcher, National Council for Scientificand Technical Research (CONICET),Rafaela Agricultural Experimental Station,National Institute of Agricultural Technology (INTA),Ruta 34 km 227, (2300) Rafaela, Santa Fe Argentinae-mail: svaltorta@rafaela.inta.gov.arTel.: +54-3492-440121Fax: +54-3492-440114

M. R. GallardoArea of Animal Production,Rafaela Agricultural Experimental Station,National Institute of Agricultural Technology (INTA),Santa Fe Argentina

Animals

Twenty-four Holstein cows in mid and late lactation were randomlyassigned to two treatment groups: control and cooled. Control cowspresented an average of 200 € 75 days in milk, of 3.42 € 2.02previous lactations, an average milk production in the weekimmediately before the beginning of the trial of 22.47 € 5.39 lcow–1 day–1 and an average body weight of 573.92 € 67.5 kg. Forcooled cows, the values were 214 € 90 days in lactation, 3.25 €1.66 lactations, 23.43 € 5.0 l cow–1 day–1 and 591.92 € 88.9 kg.

Management and feeding

All animals grazed an alfalfa pasture, in a strip system, a strip beingassigned daily to each group. A concentrate mix (70% corn grain,29.97% wheat middlings and 0.03% minerals and vitamins) andcottonseed whole with linter were fed in halves during bothmilkings, at 0500 hours and 1700 hours.

From 1000 hours until the afternoon milking all cows stayed ina pen adjacent to the milking parlor where an artificial shadestructure (80% shading cloth, 4.5 m high, orientation N–S, 4 m2/cow space allowance) was available. Water was offered ad libitum.

Cooled animals were treated with a combination of sprinklersand fans, for at least 20 min before the morning milking and 30 minbefore the afternoon milking. Fans were 0.75 kw, 1.2 m in diameterand were placed with a 30� tilt. In order to avoid any effects ofcooling, control animals entered the milking parlor before thesystem was switched on.

The grazing session lasted from after the afternoon milking untilthe following morning milking.

Measurements

Milk productions were recorded daily with an automatic Afimilksystem (Afikim, Israel). Milk composition was determined twice aweek on individual samples, which were sent to the laboratory toanalyze milk fat, protein, lactose, urea and non-fat solids. The samesamples were used for a somatic cell count. All values wereobtained with a Milkoscan autoanalyzer (Foss Electric, Hillerød,Denmark).

The rectal temperatures (TR �C) and respiration rates (RR,breaths/min) of all animals were measured weekly before and afterthe afternoon milking, at 1700 hours. The trial lasted 8 weeks.These variables were not recorded during weeks 5 and 7 becausethe weather conditions did not allow field routines to be carried out.Rectal temperature was recorded by means of clinical veterinarythermometers and RR by flank movements.

The body condition score was determined at the beginning andat the end of the trial period on a 5-point scale (Edmonson et al.1989).

The individual consumption of concentrate was measured oncea week, by weighing the amounts offered and rejected, during thewhole period.

On pasture, the amount of forage available for grazing wasmeasured by hand-plucked samples at random transects (Meijs etal. 1982; Holden et al. 1994).

Feed qualities of all feed components (pasture and concentrate)were analyzed every 2 weeks. Dry matter, crude protein, neutraldetergent fiber, acid detergent fiber, lignin, ether extract and asheswere determined (AOAC 1990).

Meteorological data

Air temperature and relative humidity data were obtained from ameteorological station located about 500 m from the experimentaldairy farm. The average daily temperature/humidity index (THI)was calculated after Amstrong (1994).

Experimental design

Production data were analyzed using the GLM procedures of SAS(1989), according to the model:

Yi ¼ uþ bþ Ti þ ei

where: Yi = all dependent variables, u = population mean, b =regression coefficient for the independent variable measured duringthe week prior to the beginning of the trial, Ti = mean effect oftreatment i, and ei = residual error (0, s2).

Differences were considered to be statistically significant withP > 0.10, since the trial was performed under grazing conditions(Kolver and Muller 1998). Similar analyses were performed formilk production data sorted according to level of heat stress: hotdays (THI � 72) and cool days (THI < 72).

Physiological data (TR and RR) were analyzed, taking accountof the effects of treatment, measuring period and their interaction.

Results

The estimated daily allowance of pasture for both groupswas of 21 kg dry matter cow–1 day–1, calculated to obtain12.5 kg dry matter cow–1 day–1 with 60% grazingefficiency.

Ingredients and the chemical composition of the dietare shown in Table 1. The diet was formulated accordingto the common feeding practices in the area, i.e. highforage diets. Concentrate and cottonseeds were added toobtain a better balance, according to the NationalResearch Council (NRC 2001) standards, for cowsproducing 25 l/day.

Milk production and composition are shown in Table 2.The treated cows produced 4.7% more milk with 9% and4% higher fat and protein concentrations, respectively.Fat and protein yields were 15% and 10% higher in thecooled animals. The body condition score (Table 2) didnot differ between treatments. Milk production for hot

Table 1 Ingredients and chemical composition of the diet offeredto control and refrigerated cows during the experimental period.Values are expressed on dry-matter basis. DM dry matter, CPCrude protein, NDF neutral detergent fiber, ADF acid detergentfiber ADL acid detergent lignin NFC = 100 – (CP + ash + etherextract + NDF), NE, net energy

Items Amount

Ingredients (%)

Alfalfa pasture (grazing) 69.3Concentrate mix 23.3Cottonseed wholes with lint 7.4

Chemical composition (%)

DM 45.3CP 21.4NDF 29.9ADF 21.7ADL 4.9Ether extract 4.3Ashes 6.4NFC 34.1NEL, (MJ/kg) 6.76

a Net energy was derived from the model of Ohio State University,Ver.5.1. (Weiss et al. 1992)

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(THI � 72) and cool (THI < 72) days is shown in Table 3.The highest differences (7%; P < 0.0954) were betweencontrol and cooled cows during hot days (n = 19). Cooledcows did not present significant differences in milkproduction on hot and cool days.

Overall TR and RR averages after the afternoonmilking were 39.6 € 0.79 �C and 71.2 € 21.9 breaths/min for the control cows and 39.3 € 0.72 �C and 54.2 €13.9 breaths/min for the cooled animals.

Table 4 shows the baseline for TR and RR, before theafternoon cooling for control and cooled cows. Nosignificant differences were detected between treatmentgroups. The differences between TR and RR valuesrecorded after and before the afternoon cooling treatmentfor control and cooled cows are shown in Table 5. The TRand RR of treated cows were significantly lower (P <0.0001).

The average air temperature, relative humidity andTHI during the whole experimental period were 23.5 €0.02 �C, 70 € 7.8% and 70.8 € 4.4 respectively.

The mean THI and TR values recorded before and afterthe treatment period, corresponding to the days when

Table 2 Milk production andcomposition, and body condi-tion score (BCS) for control andcooled cows. MUN milk ureanitrogen

Parameter Treatment P<

Control Cooled

Mean SD Mean SD

Milk (kg cow–1 day–1) 22.14 3.430 23.18 3.700 0.098Fat (%) 3.44 0.440 3.75 0.290 0.019Protein (%) 3.22 0.210 3.35 0.170 0.030Fat (kg/day) 0.755 0.095 0.870 0.088 0.006Protein (kg/day) 0.713 0.072 0.784 0.084 0.032Lactose (%) 4.74 0.210 4.78 0.220 NSSolids non fat (%) 8.71 0.370 8.86 0.370 NSMUN (mg/dl) 17.75 3.74 18.21 2.80 NSSomatic cell count (ml–1) 2,140 302 2,120 360 NSBCS change 0.010 0.23 0.018 0.23 NS

Table 3 Milk production for control and cooled cows on hot(temperature/humidity index, THI < 72) and cool (THI < 72) days

Parameter Milk production (l cow–1 day–1 Dif. (%) P<

Control Cooled

Mean SD Mean SD

THI � 72 21.4 4.3 22.9 4.1 7.0 0.0954THI < 72 22.5 4.6 23.6 4.0 4.9 0.0986Dif. (%) 5.1 3.1P< 0.0978 NS

Table 4 Baseline for rectaltemperature (TR) and respirationrate (RR), before afternooncooling for control and cooledcows. No significant differenceswere detected

Treatment TR (�C) €SD (�C) RR (breaths/min) €SD (breaths/min)

Control 39.4 0.7 72 17Cooled 39.7 0.8 77 18

Table 5 Differences in rectaltemperature (TR) and respirationrate (RR), as a response toafternoon cooling for controland cooled cows. Values werecalculated as after – before

Treatment TR (�C) SE (�C) P< RR (breaths/min) SE (�C) P<

Control 0.143 0.063 0.0330 –0.472 2.356 0.8430Cooled –0.459 0.063 0.0001 –22.969 2.361 0.0001

Table 6 Mean temperature/hu-midity index (THI), and rectaltemperature (TR) recorded be-fore and after the cooling treat-ment for control and cooledcows

Date THI TR (�C), control TR (�C), cooled

Before After Before After

Mean SD Mean SD Mean SD Mean SD

17 Jan 68.4 38.6* 0.3 38.8* 0.5 38.9* 0.3 38.7* 0.324 Jan 74.7 39.6* 0.5 39.6* 0.6 39.8* 0.4 39.1** 0.531 Jan 73.8 39.8* 0.6 40.0* 0.4 40.1* 0.5 39.2** 0.47 Feb 64.4 38.8* 0.2 38.9* 0.3 38.9* 0.3 38.9* 0.3

20 Feb 67.4 39.3* 0.7 39.4* 0.6 39.8* 0.9 39.4* 0.97 Mar 77.9 40.8* 0.5 40.7* 0.4 41.0* 0.4 40.1** 0.3

*,** Different superscripts within a row indicate significant difference (P < 0.05)

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physiological data (TR and RR) were measured, are shownin Table 6.

Discussion

The diet (Table 1) was adequate to sustain levels ofproduction considered to be acceptable for grazingsystems. However, it did not allow for an improvementin the body condition score (Table 2), which remainedlow for the physiological stage of the cows (2.4 € 0.23)(NRC 2001).

The milk yield was significantly improved by coolingin the holding pen (Table 2). Given the variabilityobserved in milk production under grazing systems, a10% difference between treatments was consideredsignificant, as proposed by Kolver and Muller (1998).These results agree with the data presented by Taraz�n-Herrera et al. (1999) for the combination of shade and apressurized spray system, which has shown both higher(Armstrong et al. 1985) and lower (Armstrong et al. 1993)results than evaporative cooling with sprinklers and fans.Keister et al. (2002) also found an increase in the milkyield of Jersey cows subjected to a sprinkler and fancooling system.

Cooling the cows before milkings produced a signif-icant increase in milk fat (9%) and protein (4%)concentrations. These results differ from other reports(Armstrong et al. 1985; Chen et al. 1993; Taraz�n-Herreraet al. 1999). However, those researchers reported increas-es in milk fat and protein yields, supporting the results ofthe present work, in which there were increases of115 g cow–1 day–1 and 71 g cow–1 day–1 in milk fat andprotein production respectively. Milk protein contentshave been shown to increase in response to a lowerminimum air temperature under the grazing systemutilized in the area where the present trial was performed,either in spring (Valtorta et al. 1998) or summer (Valtortaet al. 1997b, 2000). Also, DePeters and Ferguson (1992)reported higher milk protein contents in the San JoaquinValley area in California during the coolest months of theyear.

Grazing animals could be in continuous dietary energydeficiency, since selection pressure is particularly high insummer (Dougherty et al. 1989). This could have affectedthe response in body condition score. Comer�n et al.(2001) found that high-genetic-merit Holstein cows cansustain good milk yields, but are on a persistent negativeenergy balance, as evaluated through body conditionscore, when grazing alfalfa pastures.

After the cooling there were overall decreases of0.3 �C and 17 breaths/min in TR and RR in cooled cows,as compared to controls. The cooling system, appliedunder these particular grazing conditions, which weredifficult to manage, proved to be efficient. TR and RRafter the evaporative cooling were significantly lower(Table 5).

These findings agree with those of several trialsperformed on cows under heat stress, both under

controlled (Armstrong 1994; Armstrong et al. 1985; Chenet al. 1993; Bucklin et al. 1991; Taraz�n-Herrera et al.1999) and grazing systems (Davison et al. 1996).

These results were obtained during a mild summer.Thirty-year climatic records for the period of the trial,obtained from the weather station located at the RafaelaExperimental Station, show averages of 25.6 �C, 70% and74.7 for air temperature, relative humidity and THI,respectively.

Meteorological conditions fluctuated during the peri-ods when physiological responses were measured (Ta-ble 6). Variations in TR (Table 6) in response to coolingwere significant for the 2nd, 3rd and 6th measuring days.These days coincided with the development of heat waves(Valtorta et al. 2002). Highly producing animals areparticularly sensitive to extreme weather events and torapid changes in conditions (Hahn 1999), which couldimpact thermoregulation and feeding behavior (Nienaberet al. 2001).

This information shows that evaporative cooling,which is efficient for housed animals, is also appropriateto improve yields and animal well-being under grazingsystems, when utilized before milkings. These resultscould probably be magnified during hotter summers.

Acknowledgements The authors wish to acknowledge Dar�o Arias,Daniel Calpachay and Pedro Ludue�a for their help in managingthe animals and obtaining the field information, and M�nicaGagiotti and Oscar Quaino for their assistance in laboratory andstatistical analyses.

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