Guide for the Care and Use of Agricultural Animals in Research and ...

cept for situations in which high relative humidity doesnot cause animal health concerns. Conversely, ventilationrate during cold weather should be sufficiently lowto ensure that the relative humidity does not fall to alevel that causes animal health concerns, unless needsfor air quality or condensation control necessitate ahigher rate. Atmospheric humidity does not ordinarilybecome a significant factor in effective environmentaltemperature until the air temperature approaches thetemperature of the animal’s surface, in which case theanimal will depend almost entirely on evaporative heatloss to maintain thermal equilibrium with the environment.The use of fans to promote air movement can be beneficialduring hot weather if there is too little naturalair movement. Direct wetting is effective in decreasingheat stress on cattle and pigs; however, it can cause thedeath of poultry. Wetting is best accomplished by watersprinkled or dripped directly on the animals. Mistersand evaporative coolers specifically designed to reduceair dry-bulb temperature are also used to reduce heatstress on agricultural animals.Correctly designed and maintained sunshades protectanimals from heat stress by reducing solar radiationload. Trees, if available, are ideal sunshades. Artificial,roofed shades are acceptable.Mechanical ventilation requires proper design andoperation of both air inlets and fans for proper distributionand mixing of the air and thus for creatinguniform conditions throughout the animal living space.Mechanical ventilation, with fans creating static pressuredifferences between inside and outside the house,brings in fresh air and exhausts air that has pickedup heat, water vapor, and air pollutants while passingthrough the building. Mechanical ventilation, if properlydesigned, provides better control of air exchangefor enclosed, insulated animal houses in colder climatesthan does natural ventilation. The effectiveness of naturalventilation in cold climates will depend on the designand orientation of the enclosure, as well as thespecies and number of animals housed and the stage oftheir life cycle.Natural ventilation uses thermal buoyancy and windcurrents to vent air through openings in outside wallsor at the ridge of the building. Natural ventilation isespecially effective for cold animal houses (i.e., housesin which no heat is supplied in addition to animal heat)in moderate climates; however, insulated walls, ceilings,and floors are often recommended to minimize condensation.The air exchange rate needed to remove thewater vapor generated by animals and evaporation ofwater from environmental surfaces often brings air temperatureinside such houses down to values near thoseoutdoors. If waterers and water pipes are protectedfrom freezing, the practical low operating temperatureis the point at which manure freezes, although this temperaturewould be too cold for some species or stagesof the life cycle. Automatic curtains or vent panels,HUSBANDRY, HOUSING, AND BIOSECURITYinsulated ceilings, and circulating fans help to regulateand enhance natural ventilation systems.During cold weather, ventilation in houses for neonatalanimals should maintain acceptable air qualityin terms of water vapor and other pollutants withoutchilling the animals. Air speed should be less than 0.25m/s (50 ft/min) past very young animals. There shouldbe no drafts on young poultry or pigs.During hot, warm, or cool atmospheric conditions,ventilation of animal houses should maintain the thermalcomfort of the animal to the extent possible. Ideally,the ventilation rate should be high enough to preventindoor temperature from exceeding outdoor temperature(temperature rise limit; Curtis, 1983) by morethan 3°C (5°F) when the atmospheric temperature isabove 32°C (90°F) for small animals and above 25°C(78°F) for larger ones. In arid and semi-arid regionswhere the potential for evaporative heat loss is great,air temperature may peak at over 43°C (110°F) for 1or 2 d or longer without affecting animal well-being ifanimals have been acclimatized by chronic exposure.Ventilation system design should be based on buildingconstruction and the rates of water vapor and heatproduction of the animals housed (Curtis, 1983; Hinkleand Strombaugh, 1983). The frame of reference is theanimal microenvironment. For example, the outdoorcalf hutch is a popular accommodation for dairy replacementheifer calves in most parts of the continentalUnited States. Although the hutch provides a coldmicroenvironment for calves during winter in northernlatitudes, the calf is nonetheless comfortable if caredfor correctly (MWPS, 1995). In closed houses duringhot periods, additional ventilation capacity (up to 60 ormore air changes/hour) may be necessary.In enclosed animal houses, both environmental temperatureand air quality depend on the continuousfunctioning of the ventilation system. An automaticwarning system is desirable to alert animal care and securitypersonnel to power failures and out-of-toleranceenvironmental conditions (Clark and Hahn, 1971), andconsideration should be given to having an on-site generatorfor emergency use.The relative air pressures between animal areas andservice areas of a building housing animals should beconsidered when the ventilation system is designed tominimize the introduction of airborne disease agents orair pollutants into the service area. Advice of a qualifiedagricultural engineer or other specialist should besought for the design of and operating recommendationsfor ventilation equipment.Air QualityAir quality refers to the nature of the air with respectto its effects on the health and well-being of animalsand the humans who work with them. Air quality istypically defined in terms of the air content of certain19