Keeping Cows Cool? Where Do I Start?
Keeping Cows Cool,Where do I Start?
J.F. Smith
Department of Animal Sciences and Industry
Kansas State University
J.P. Harner III
Department of Biological and Agricultural Engineering
Kansas State University
M.J. Brouk
Department of Animal Sciences and Industry
Kansas State University
Heat stress occurs when a dairy cow’s heat load isgreater than her capacity to lose heat. Heat stress effectsinclude: increased respiration rate, increased water intake,increased sweating, decrease in dry matter intake, slower rateof feed passage, blood flow to internal organs, milk productionand poor reproductive performance (Hansen et al., 1992). Thelower milk production and reproductive performance causeeconomic losses to commercial dairy producers.
Water Availability
Providing access towater during heat stressshould be the first step.Lactating dairy cattle willtypically require between35 and 45 gallons of waterper day. Studies completedin climatic chambers showthat water needs increase1.2 to 2 times when cowsare under heat stress(Beede, 1993). A watersystem needs to be designedto meet both peakdemand and daily needsof the dairy. Making wateravailable to cows leavingthe milking parlor willincrease water intake bycows during heat stress.Access to an 8-foot watertrough is adequate formilking parlors with25 stalls per side. Inwarmer climates the followingformula is used tocalculate the required tankperimeter: group size x .15x 2 = tank perimeter in feet.In cooler climates, onewaterer or 2 feet of tankperimeter is adequate forevery 15 to 20 cows. Anideal situation would be tohave water available atevery crossover in freestallhousing with 100 feet between crossovers. (Smithet al., 2000 and MidwestPlan Service, 1997).
Shades
Providing shade inhousing areas and theholding pen is the secondstep. Cows housed in drylotor pasture situations shouldbe provided with solidshade. Florida researchers(Roman-Ponce et al., 1977)found that cows housedwith shade had higher milkyields and conception ratesthan non-shaded cows.Natural shading providedby trees is effective, butmost often shades areconstructed from solid steelor aluminum. Providing38 to 48 square feet of solidshade per mature dairy cowis adequate to reduce solarradiation. Shades should beconstructed at a height of aleast 14 feet with a northsouthorientation to preventwet areas from developingunder them (Armstrong,1993). Using a more porousmaterial like shade cloth orsnow fence is not as effectiveas a solid shade.(Kelly, 1958 and Welchertet al., 1965).
Methods to Cool Cows
Different coolingsystems have been testedin a wide variety of climates(Armstrong, 1994,Bray et al., 1994; Brouk etal., 1999; Igono et al.,1987; Lin et al., 1998;Strickland et al., 1989; andTurner et al., 1992). Researchershave tried everythingfrom high-pressuremisters to low- pressuresprinklers or soakers toapply water. These havebeen used along with fansystems to aid in the evaporationof water off the cows’backs and in the surroundingair. As humidity in theenvironment increases, theability to evaporate waterdecreases. In general lowpressuresprinkler or soakersystems can be used to soakthe cows along with fans inany climate to cool cows.The effectiveness of thesesystems can be seen byvisiting the local pool on ahot windy day. Childrenwill leave the pool andbecome cold as the waterevaporates off their skin.Just watch these childrendevelop goose bumps asthey search for their towels.Once they dry off theybecome warm and jumpback in the pool to start thecycle again.
The same technique isused in cooling dairy cattleby wetting cows intermittently.It must be rememberedthat high-pressure systems cool the air aroundthe cow, and work best invery arid climates. Whenlow pressure and highpressuresystems are combined,the ability to evaporatemoisture off the cowsbacks may be reduced.Unless a dairy is located inan arid climate, low-pressuresystems are probablythe most economical andpractical way of coolingcows.
Holding Pen and Exit LaneCooling
The holding pen iswhere dairy cows experiencethe most heat stress.Arizona researchers(Wiersma and Armstrong1983) concluded that whencows were cooled in theholding pen, milk productionincreased 1.7 poundsper day during the summer.Low-volume sprinklers andfans can be used to wetcows and speed evaporationof the water off the cowsbacks. Fans should operatecontinuously providing aminimum of 1,000 CFMper cow. Fans should bemounted overhead andblow downward at a 30degree angle. Fans of 36-to 48-inches in diameter aremost common. Fans aretypically placed side byside spaced 6 to 8 feetapart. The distance betweenrows of fans is 20 feet for30 and 36-inch fans and40 feet for 48-inch fans.Water can be sprayed ontothe cows using a PVC gridof 360 nozzles. Water isapplied one minute out ofevery six minutes.
Cooling cows as theyexit the parlor provides anadditional 15 to 25 minutesof cooling per milking(Armstrong, 1993). Typicallythree to four nozzlesare installed in the exit lane,with a delivery of approximately8 gallons of waterper minute at 35 to40 pounds per square inch.The nozzles are turned onand off with an electric eyeor wand switch as the cowpasses under the nozzles. Ifproperly installed, sprinklershould wet the top andsides of the cow , the udderwill remain dry, the waterwill not interfere with postdipping.
FreeStalls
Freestall housingshould be constructed toprovide good naturalventilation. Sidewallsshould be 14 ft high toincrease the volume of airin the housing area. Thesidewalls should be open75 to 100 percent. Fresh airshould be introduced at thecows’ level. Curtains on thesides of freestall barnsallow grater flexibility incontrolling ventilation.Because warm air rises,steeper sloped roofs provideupward flow of warmair. However, roofs with slopes steeper than a6/12 pitch prevent incomingair from dropping intothe area occupied by thecows. Roofs with slopesless than 4/12 may causecondensation and higherinternal temperatures in thesummer. Roof slopes forfreestall housing shouldrange from 4/12 to 4/16.Providing openings in endwalls and alley doors willimprove summer ventilation.Gable buildingsshould have a continuousridge opening to allowwarm air to escape. Theridge opening should betwo inches for each 10 feetof building width. Naturallyventilated buildings shouldbe spaced 1.5 to 2 times thebuilding width (Armstronget al., 1999).
Adding fans and asprinkler system can provideadditional cooling infreestall areas. Freestallbedding must not becomewet. Typically, a sprinklersystem or soaker systemcan be located over thelockups, and fans could beused over the freestalls,lockups, or both to aid inthe evaporation of water offthe cows’ backs. Water isapplied three minutes out ofa 15-minute cycle. Thesespray and fan systems areturned on and off with athermostat at 70-75° F(Brouk et al., 1999).
Which Groups of Cows DoI Cool First?
A commonly askedquestion is which cowsshould be cooled first?Ideally, all lactating and drycows should be cooled ifpossible. All lactating cowswill respond to coolingduring heat stress. Butoften producers are facedwith the reality that theyhave a limited budget andhave to decide which groupof cows to cool. The firstgroup to be cooled shouldbe the close-up cows, thosewithin three weeks ofcalving. Dry matter intakeprior to calving is critical toensure that the up cominglactation is successful.Remember that we typicallyloose dry matterintake during heat stress.The second group to becooled should be the freshand early lactation cows.These cows are establishingthe peak milk production ofthe lactation. For everypound of peak milk productionthat is lost, 250 poundsof milk production will belost over that lactation. It isnot uncommon for producersin Kansas to lose 10pounds of peak milk productionduring heat stress ifcows are not cooled. That isequivalent to 2,500 poundsof milk over the lactation.Once the early lactationcows have been cooled, themid- and late-lactation cows should be cooled.Here is a list of prioritiesfor reducing heat stress:
References
Armstrong, D.V., P.E.Hillman, M.J. Meyers, J.F.Smith, S.R. Stokes and J.P.Harner III. 1999. Heat StressManagement in FreestallBarns in Western United States.Proceedings of the 1999 WesternDairy Herd ManagementConference. Las Vegas, NV.
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Source: Kansas State University
Author: Harner, Murphy, Smith