Alleviating heat stress is critical to milk production. Heat stress from high environmental temperatures can be compounded by mistakes in managing and feeding the cows. Water is your first concern during periods of high temperatures. Water physical properties—heat conductivity and latent heat of vaporization—help transfer heat from the body of the animal to the environment

Garcia, Alvaro

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South Dakota State UniversityOpen PRAIRIE: Open Public Research Access InstitutionalRepository and Information ExchangeExtension Extra SDSU Extension1-1-2006Dealing with Heat Stress in Dairy CowsAlvaro GarciaSouth Dakota State UniversityFollow this and additional works at: http://openprairie.sdstate.edu/extension_extraThis Other is brought to you for free and open access by the SDSU Extension at Open PRAIRIE: Open Public Research Access InstitutionalRepository and Information Exchange. It has been accepted for inclusion in Extension Extra by an authorized administrator of Open PRAIRIE: OpenPublic Research Access Institutional Repository and Information Exchange. For more information, please contact michael.biondo@sdstate.edu.Recommended CitationGarcia, Alvaro, "Dealing with Heat Stress in Dairy Cows" (2006). Extension Extra . Paper 122.http://openprairie.sdstate.edu/extension_extra/122Dealing WithHeat Stress in Dairy CowsAlvaro GarciaExtension dairy specialistReducing heat stressWater requirements parallel the increase in ambienttemperature. As the temperature rises from 86 to 95 F, water intakemay increase from 21 to 32 gallons.  If cows haveaccess to an outside lot, it is very important that thewater be close to shade and the feed bunk.  Higher producing cows are more prone to suffer fromheat stress because they generate more heat as aresult of their higher feed intake and thus will requiremore drinking water.  The water should be fresh, clean, and free of contam-inants.  If you are using well water, have it tested forits safety for cattle.  Try to keep cows that are on out-side lots or pasture away from ponds.  Ponds pose arisk to cattle health: They often have poor qualitywater, and they also can increase the incidence ofmastitis and higher somatic cell counts in your herd.Under current drought conditions, if cows are drink-ing water from sources that are not rural water sys-tems, it is necessary to run a “livestock suitabilitytest” (sodium, alkalinity, sulfates, nitrate nitrogen,electrical conductivity and hardness) to determine ifit is safe for livestock. Contact your county educatorsfor more details.Alleviating heat stress is critical to milk production.Heat stress from high environmental temperaturescan be compounded by mistakes in managing andfeeding the cows.  Water is your first concern during periods of hightemperatures.  Water physical properties—heat con-ductivity and latent heat of vaporization—help trans-fer heat from the body of the animal to the environ-ment. Dry matter intake of lactating cattle is affected whenambient temperatures are outside of the cow’s “com-fort zone” (41 to 68 F).  When ambient temperaturesincrease beyond 68 F, the cow typically goes off feed.Dry matter intake can decrease by 0.17 lb for eachdegree above 68 F.  During severe heat stress, totalintake and milk production may decrease by morethan 25%.  It is estimated that for every 1 lb decrease in dry mat-ter intake 2 lb of milk production are lost. Some responses of cattle to heat stress, such as panti-ng, may actually increase heat production in theirbodies.  Other changes, such as reduced dry matterintake, selective consumption (higher energy densefeeds), reduced activity, reduced metabolic rate, andcooling strategies, will reduce heat production. C O L L E G E  O F  A G R I C U L T U R E  &  B I O L O G I C A L  S C I E N C E S  /  U S D AExEx 4024Dairy ScienceShading the feed manger increases cow comfortwhile eating and may encourage higher feed intakes.A combination of a sprinkler system spraying towardthe cows and fans to increase airflow can be used todissipate the heat from the cow.  Spray water awayfrom the feed so that it does not become wet.  Tryalways to keep udders dry to decrease the incidenceof mastitis.  Make sure there is enough traction in thefloor to prevent injuries due to slipping. Heat stress and the dietHeat is produced as a result of microbial fermenta-tion in the reticulo-rumen.  Low quality, stemmy for-ages generate more heat of fermentation inside theanimal, contributing to the animal’s total heat load. Heat is used to maintain body temperature whenambient temperatures are low (below 40 F).  Butwhen ambient temperatures are high the cow needs tomaintain its body temperature within biological limitscompatible with life.  Her options are limited.  She can drink more freshwater (water evaporation from the body dissipatesheat).  She can look for cool spots like ponds, shade,and places with good air circulation, or she candecrease her dry matter intake. Close confinement in the holding pen contributes toheat stress.  You might be able to cool your cows by acombination of air movement (fans) and water orshade.  Sprinkling the cows lightly, without also providingadequate air circulation, can worsen the situation bycreating a hot and humid environment that will notallow heat to dissipate.  This is shown in Figure 1,where 95 F and 85% relative humidity result inmedium heat stress.  The same temperature (95 F),with 91% relative humidity index results in severeheat stress.  Increasing airflow by the addition offans is a partial solution to this problem. Shading from direct sunlight is also very important.Research data are limited as to the benefit of shade,but in one Arizona study, shade over the feed bunkimproved milk production by 7.5% as compared toa control situation with no shade.  During summermonths, cows provided with no shade consumed18% more water per day than cows given shade.  Permanent shades can sometimes be a problem asthey can concentrate moisture and manure and mightincrease the incidence of mastitis.  Portable shadesystems can be constructed with either wood or weld-ed pipes.  Shade cloth that provides at least 80%shade is available. 72    72    73    73    74    74    75    75 72    72    73    73    74    74    75    76    76    77    78    78    79 72    72    73    74    75    75    76    77    78    78    7972    73    74    75    76    77    78    7975    76    77    78    7977    78    797980     81     81     82     83     84     84     8579     8079     80     81     82     83     84     85     86      86     87     88     8980     81     82     83     84     85     86     87     88     8980     82     83     84     85     86     87     8880     82     83     84     86     87     8881     83     84     86     87     8984     85     87     8888     880 5 10     15     20    25    30    35    40    45    50    55    60    65    70    75    80    85    90    95   100DEGF7580859095100105110115120RELATIVE HUMIDITY1 THI=(Dry-Bulb Temp. C) + (0.36 dew point Temp. C) + 41.29090    91    92    93    94   9590    91    92    93    94    95    97    98    9989    91    92    93    95    96    9790    91    93    95    96    9789    91    93    94    96    9890    91    93    94    96    97Medium StressMild StressSevere StressFig 1.  Temperature Humidity Index (THI)1 for dairy cows.  Modified from Dr. Frank Wiersma (1990), Department ofAgricultural Engineering, University of Arizona, Tucson.High quality forages are digested faster and result inless heat being produced.  So, whenever feed intakedecreases due to heat stress, consider enriching theration.  Energy is a particular concern, as most of it isderived from the fermentation of forages within therumen. Increasing the energy density might requiregreater amounts of concentrate and/or byproducts.   But keep in mind that shifting the grain/forage ratiomay increase the risk of not having enough rumen“scratch factor” (effective fiber) to optimize rumina-tion. When the rumen mat formation is inadequate, salivaproduction decreases (less chewing activity).  Thisdecreases rumen pH and allows more grain to be fer-mented in the abomasum and intestines.  Adequateparticle size and the use of buffers such as sodiumbicarbonate are critical in these “hot rations” to mini-mize the risk of digestive disorders such as acidosisand displaced abomasums.  Sweating aids in heat dissipation, and sodium andpotassium are secreted in sweat.  This will be a prob-lem particularly with high producing dairy cows,which secrete more of these minerals in milk.  Whenenvironmental temperatures are above 86 F, make surethat diets contain at least .25 lb of white salt per cowper day.  Plenty of fresh, high quality water shouldalso be available.  Test it; you don’t want wateralready high in sodium. Alleviating heat stress in dairy cattle is a challenge inevery South Dakota summer.  Maintaining optimumnutrient balances and providing highly palatable,digestible feeds and ample supplies of fresh, cleanwater, along with shade and ventilation, will go fartoward keeping your cows comfortable and their milkproduction up.ReferencesBray, D.R., and R. Bucklin. 1996. Recommendations for coolingsystems for dairy cattle. Fact Sheet DS-29. University ofFlorida Cooperative Extension Service, Gainesville.Muller, C.J.C., A. Botha, and W.A. Smith. 1994. Effects of shadeon various parameters of Friesian cows in a Mediterranean cli-mate in South Africa. 1. Feed and water intake, milk produc-tion and milk composition. S Afr J Anim Sci 24(2):49.Nutrient Requirements of Dairy Cattle. 2001. National Academyof Sciences, Washington, D.C.Pennington, J.A., and K. VanDevender. 2000. Heat stress in dairycattle. FSA3040-1M-1-99R. University of Arkansas.This publication and others can be accessed electronically from the SDSU College of Agriculture & Biological Sciences publications page athttp://agbiopubs.sdstate.edu/articles/ExEx4024.pdfor from the Extension Service Drought Information Website athttp://sdces.sdstate.edu/drought/South Dakota State University, South Dakota counties, and U.S. Department of Agriculture cooperating.  South Dakota State University is an AffirmativeAction/Equal Opportunity Employer and offers all benefits, services, education, and employment opportunities without regard for race, color, creed, reli-gion, national origin, ancestry, citizenship, age, gender, sexual orientation, disability, or Vietnam Era veteran status.ExEx4024, 2004, 2006

Dealing with Heat Stress in Dairy Cows

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Dealing with Heat Stress in Dairy Cows

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