Advances in Sheep and Goat Medicine

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Ventilation of Sheep and Goat Barns

Eldridge R. Collins, Jr, PhD*

Ruminant livestock such as sheep and goats have a marked ability to alter their thermoneutral zone in response to their previous environmental history. Therefore, with the possible exception of that for the newborn animal, thermal housing requirements for sheep and goats depend to a large extent on the temperature to which the animals have grown accustomed. As long as sheep and goats are provided with a clean, dry, and draft-free resting area, temperature is not the primary consideration for an acceptable barn environment. Most barn environmental problems arise when growers attempt to apply human standards for warmth; cracks are tightly sealed, building humidity increases, and the levels of gases, dust, and airborne bacteria increase. In addition, temperature tends to fluctuate within the barn because of weather changes, and animals do not have the opportunity to adapt to a continuously cold or cool condition. Consequently, they are disposed to illnesses that contribute to reduced thriftiness, economic losses, and sometimes death. This article focuses on proper methods of maintaining an acceptable environment in both "cold" and "warm" barns. PRINCIPLES OF GOOD VENTILATION Ventilation is a major part of the overall barn environmental control system. Proper ventilation ensures the exchange of fresh air based on the environmental requirements of the animals housed and in concert with the outdoor climatic conditions at any particular moment. Major functions of the ventilation system are to provide fresh, clean air for the animals, prevent drafts, remove moisture from inside the building, remove heat during hot weather, and remove odors, dust, airborne disease organisms, and gases from animals and waste. Major challenges to barn ventilation in the winter are moisture removal and odor control, while maintaining a stable, draft-free temperature, and in summer to keep the inside barn environment at or near outside ambient conditions. Environmental control systems consist of six major parts: (1) a method of creating air exchange through the building (fans, wind, or natural air buoyancy); (2) a method of directing the air where it is most desirable (air inlets); (3) *Professor and Extension Agricultural Engineer, Department of Agricultural Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia Veterinary Clinics of North America: Food Animal Practice-Vol. 6, No.3, November 1990

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controls (thermostats or other automatic controls, or manual adjustment); (4) a method of providing energy to the barn space during cold weather to increase air moisture-holding capacity and provide acceptable environmental temperature (space heaters, zone heaters, solar energy, or body heat); (5) an efficient, properly installed insulation package, suitable for the building environmental goals; and (6) a proper understanding by the operator of the definition and goals of good ventilation practice. Each factor is of importance in the success of ventilating barns, although the emphasis varies depending upon the type of barn and ventilation system involved. SITING OF BUILDINGS Building location is an important factor in facility development and often dramatically influences environmental control and management. Four factors should be considered when selecting a site for buildings: (1) orientation, to take advantage of prevailing air movement (for natural ventilation) and to minimize drafting effects of strong winter winds on mechanical ventilation equipment; (2) screening out solar heat in summer but allowing utilization of solar gain during winter; (3) adequate separation from other structures or obstacles; and (4) location on high ground to minimize effects on air flow by trees, hills, and structures, and to assure dry conditions around and under the building. Wind Direction Most producers are aware of wind direction at their farms for the various seasons of the year. "Wind roses" (Fig. 1) are available from US Weather Bureau publications and other similar government services that provide a graphic representation of the percentage of time that winds come from each of the 16 points of the compass during a particular time of the year at given locations. Based solely on wind direction, it is most desirable to orient a naturally ventilated building with the long axis of the building perpendicular to the generally prevailing winds. Most desirable wind pressure differences occur when wind strikes the building side wall and is perpendicular to the building centerline. Fortunately, wind directions are often opposite for summer and winter in many areas of the United States, so if a building is properly oriented for winter, it will also be properly oriented for summer ventilation. Curtains, movable panels, or other closures are provided for protection from cold winter winds, and if one side of the building will be totally or partially open yearround, the open side should face away from prevailing winds. Direction of prevailing winds, especially during winter, should also be considered in locating mechanically ventilated buildings. A major concern in planning these buildings should be, where possible, to place small, continuously running or slowly rotating, variable-speed winter fans on the downwind side of the building to maintain rated fan capacity, or to prevent backdrafting, reverse fan loading, and damage to fan motors. Solar Orientation Sheep and goats, especially larger animals during breeding, gestation, birthing, and finishing, are sensitive to extremes of heat during the summer months. Hot weather conditions during this season, coupled with heat produced by animals in the buildings, make it important to provide well-designed mechanical ventilating equipment and/or a building design that ensures good natural air movement. However, often little consideration is given to orienting

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the building to prevent hot conditions caused by solar heat loads during the summer. If the building is properly oriented and the ceiling or roof is suitably insulated and vented, heat stress can be minimized. An unnecessary source of heat stress is thermal radiation from hot building surfaces. Thermal radiation is energy released in the form of wave motion. The greater the temperature difference between building surfaces and the animals, the greater the amount of heat transfer between the two. During the summer, energy radiated from the hot surfaces of the building (ceiling, walls) strikes interior components of the building and the animals themselves, where it is absorbed and results in a temperature rise. During winter, the reverse occurs, whereby the animals or the warmer interior surfaces of the building radiate energy to cold surfaces such as an uninsulated ceiling or roof. Orientation (azimuth) of the building can help minimize this effect. Although solar heat load on the roof of a north-south oriented building is slightly greater than on an east-west oriented building owing to more direct radiation on a greater proportion of the roof, good attic insulation and venting, or under-roof insulation, help to eliminate this as a major problem. However, the difference in orientation of the roof could be a significant problem owing to solar heat gain on side walls of north-south oriented structures. Solar loading of north-south oriented buildings, which depend on natural ventilation through open curtains or movable panels, is often a major problem. Animals in pens, and pen surfaces and equipment, must be exposed to solar radiation during much of the morning and afternoon unless curtains and panels are closed to block out solar exposure. An unacceptable result is that ventilation is blocked in the process. All materials, even insulation, conduct heat. Insulation merely retards heat How through a wall, ceiling, or roof, so even totally enclosed buildings with well-insulated walls become hot when there is sun exposure on the exterior walls during much of the day. Naturally ventilated buildings using adjustable curtains or other closures allow sun to penetrate into the building much of the morning and afternoon during summer when buildings are oriented on a northsouth azimuth (Fig. 2). Building Hoors, partitions, equipment, and other interior surfaces absorb solar heat and contribute to a hot building environment that lasts until well after sundown. If curtains or panels are raised to block sun in the morning or afternoon, natural ventilation will be impeded, and the hot curtain or panel surfaces will radiate heat to the building interior. Therefore, buildings should be located to minimize summer solar heat gain. Buildings located on an east-west azimuth can be engineered with sufficient roof overhang to prevent interior sun exposure during the summer, while allowing desirable sun penetration during the winter. The relatively smaller, and typically closed and insulated, east and west end walls will receive relatively short sun exposure in the morning and afternoon, and because their surface area is far less than that of the sides of the building, they will contribute less to internal building heating. With the importance of both prevailing winds and solar screening conceded, a general recommendation is to site naturally ventilated buildings with the long axis running east-northeast to west-southwest. Other site location conditions may occasionally dictate otherwise. Separation from Other Structures and Obstacles The location of grain bins, silos, and other farm buildings can greatly affect air How around a livestock structure. This may be especially critical with naturally ventilated buildings, and it will retard displacement of stale exhaust air by fresh air near intakes on mechanically ventilated buildings. One should attempt to locate naturally ventilated buildings upwind of other buildings or obstructions that could block air How. If they must be placed

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Figure 1. Surface wind roses for the United States, January (A) and July (B). Wind roses show percentage of time wind blew from the 16 compass points. Number in circle is percentage of time calm. • = calm less than 0.5% of the time. US Weather Bureau statistics from hourly observations, 1951-1960.

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limit clear area to less than that required, opening slots should be designed and constructed in the top of the wall on each side of the building. Eave openings should be protected against direct winds, which can cause undesirable drafts in animal pens. Use of fascia boards and placement of soffit boards under the eaves, or forcing air to travel through a hollow wall cavity before reaching the

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opening, are effective ways of reducing this problem. Adjustable eave opening doors (Fig. 11) are also useful, especially in severe climates to reduce drafting and blowing snow. However, care must be taken that eave opening doors are never completely closed, and are partially closed only during windy, severe weather. Monoslope Roof Buildings Monoslope roof buildings have no ridge vent, so they ventilate with cross flow of air in both winter and summer. During winter, air is allowed to enter through the rear wall eave vent and exit at the front (high) wall. Monoslope buildings are often constructed with an open high side, where air flow enters the building through the back (low) wall eave inlet or open front, and exits at the top of the front wall. The low wall should be closed and facing the wind during winter, and the high (open) side should face the wind during summer to catch prevailing summer breezes. According to US Weather Bureau data (see Fig. 1), in most locations of the United States, open front monoslope buildings could be constructed for satisfactory performance with the high side facing south to take best advantage of wind effects and the solar considerations discussed earlier. MECHANICAL VENTILATION SYSTEMS In very cold climates, warm housing will often be maintained for lambing and kidding, and mechanical ventilation systems will be required. These systems enable housing to be maintained above freezing, usually at temperatures of 45° to 60°F. Good mechanical ventilation should include the following: (1) an insulation package suitable for the local climate and building purpose; (2) a system of fans to "pump" air through the building at a rate low enough in winter to remove moisture and gases released in the building without undue wasting of heat, with intermediate levels of ventilation capacity for milder weather conditions in spring and fall, and maximum ventilating capacity for hot weather to maintain indoor conditions as close to outdoor conditions as possi-

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ble; (3) an air inlet system that can be adjusted by either manual or automatic means to work in harmony with the amount of ventilation capacity at any given time to maintain the necessary inlet velocity and direction to prevent drafts and maintain good room air mixing; (4) a system of thermostats or other controls to properly control and cycle fans and heaters; and (5) two heating systems, one for general space heating and the other to provide zone heat, such as lamps, to newborn animals. Insulation levels typically required range from wall values of R = 14 to R = 20 and ceiling values from R = 22 to R = 33. Careful attention to good installation practices for insulation and vapor retarders must be provided, along with good fitting of doors and other openings, to assure a minimum of air leakage. Air should only enter the building through the planned fresh air inlets. Otherwise, the ventilation system will not work to its best capability. Three levels of ventilation should be provided with the fan systems. The winter ventilation rate should be the lowest level and should assure at least 25 cubic feet per minute (cfm) per 1000 pounds of animal weight at all times. Winter ventilation is best provided by one or more (depending on building size) small, continuously running fans. All fans should be selected for air deliveries based on 0.1 to 0.125 inches (water column) static pressure (sp). A second level of ventilation should be provided for mild winter days, and for spring and fall, and should be sized on the basis of an additional 75 cfm per 1000 pounds of animal weight. Fans should be operated by thermostats or other controllers to be activated in steps as room temperature rises. The third level of ventilation should be provided for summer conditions. If the building is permanently enclosed, size additional fans on the basis of a total 200 cfm per 1000 pounds of animal weight. An alternative summer ventilation scheme frequently used for sheep and goat housing is to provide well-insulated, tightly sealing wall panels that can be opened and operated as described for wall closures in the discussion on natural ventilation. Fan ventilation units, by themselves, are inadequate unless they are combined with a good air inlet system. Air inlets are openings through which fresh, incoming ventilation air is uniformly and equally distributed into the building room(s). The inlets should be adjustable to always maintain a design velocity of 600 feet per minute, which means that open inlet area of 24 square inches must

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be provided for each 100 cfm of fan capacity in operation at a given time. Several different types of inlets work satisfactorily. The perimeter slot inlet (see Fig. 11) is installed on both sides of the building and allows air to How over the wall plate and through a crack between the ceiling and inside wall. The adjustable insulated baHle is used to adjust the effective inlet slot to suit the amount of fan capacity in operation. The baHle should be made of an insulating material to prevent condensation or frosting of moisture caused by the cold fresh air. Adjustment of the baHle is usually made by means of a hand-operated winch or automatically by commercial sensing devices. To help maintain proper inlet slot adjustment, a manometer (or sp gauge) should be installed close to the adjustment winch. By maintaining the room operating sp at 0.04 to 0.1 inches, the correct inlet velocity can be maintained at all but the minimum air How rate. Because of the near impossibility of sealing all cracks in the room, and other construction difficulties, it is not usually possible to obtain the theoretic air velocity through the inlets at the minimum cold weather ventilation rates. At these times, the air velocity through the inlets will not promote adequate blending and mixing with room air. To correct this problem, stirring fans, mixing tubes, or other similar means should be provided to assure a high standard of ventilation (see discussion in following section). Air must be constantly moved through the room, and heat must be provided to remove moisture during the winter while maintaining a given temperature. Although some heat will be introduced to the room by the animals, population is usually low in lambing and kidding rooms, and lights and other electrical equipment will generally provide only a small portion of the total heat requirement. Therefore, it will be necessary to provide additional supplemental heat if animals are to be kept comfortable and satisfactory ventilation is to be achieved. A common method of space heating is with ceiling-suspended gas or electric unit heaters sized to account for heat losses through building surfaces and ventilation air. Controls should be selected that are designed specifically for livestock applications, because they are generally simple and reliable. Controls should be located in the center of the building, away from cold walls, direct sunlight, fresh air inlets, heater discharge, or other factors that may cause sensors to perceive a nonrepresentative average room temperature. Controls should also be located as close to animal level as possible, but out of their reach and away from possible physical damage caused by routine cleaning and other operations. Mechanical ventilation of livestock buildings involves highly technical design, which is beyond the scope of this article. An excellent and detailed treatment of the topic is provided by Midwest Plan Service. 7

IMPROVING VENTILATION IN EXISTING BUILDINGS Problems often become apparent in existing buildings, both those constructed specifically for sheep or goats and those converted from other uses. Often, it is impossible for the grower to obtain an ideal environment in these structures because of air leaks, poor insulation, building Hoor plan, and other features. There are, however, a few relatively easy steps that can sometimes be taken to improve a less-than-ideal situation. The importance of ridge ventilation in gable roof buildings was discussed earlier. One of the improvements that should be considered first in existing gable roof buildings without ceilings is the addition of a ridge ventilation slot.

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The guidelines given in the earlier section can be used to determine the opening size. It is important to provide the needed companion wall openings and winter eave openings. Very wide buildings are often plagued with nonuniform air distribution problems in both cold and hot weather. Improved distribution can be obtained by means of circulation fans. Three methods are generally available for this purpose: (1) Hang fans from the truss chords to blow air longitudinally throughout the building. Select fans that have totally enclosed motors, sized on the basis of 1 cfm per square foot of building floor area. Use an even number of fans, and hang half on one side of the building to direct air in one direction, and the other half on the other side to direct air in the opposite direction. For example, a 60 X 100 foot barn (6000 ft2) could be equipped with four hanging 1500-cfm fans, two located in line on each side of the barn approximately 20 feet from the barn exterior wall. (2) A pressurized duct system may be used to circulate air through the barn and provide improved mixing during cold and hot weather. Provide one unit, or a combination of units, to supply 1 cfm per square foot of building area. Commercial equipment is available that combines a fan unit and polyethylene duct tube with punched holes to distribute the recirculated air uniformly along the full length of the tube. The same equipment can be adapted to serve as a fresh air delivery system during hot weather if the natural ventilation system is unable to provide satisfactory air movement. (3) Stirring units (four) can be assembled (Fig. 12) using fans suspended horizontally from the lower ceiling chords, to blow downward against a 0.5inch-thick plywood square measuring two fan diameters in each direction. The plywood sheet should be located beneath the fan at a distance of five eighths of a fan blade diameter. Size the stirring fan units on the basis of 1 cfm per square foot of building floor area. The length-to-width ratio of the area covered by each fan should be 1: 1, but no more than 1.5: 1. For example, for the case stated in method 1, two stirring fans of 3000 cfm each could be installed along the centerline of the building. Fans would be installed 25 feet from each end and 50 feet apart. Length-to-width ratio of the area covered by each fan would be 1.2: 1 (60 ft/50 ft). These three methods may be helpful in improving mixing and reducing "dead" spots within the building environment. Care must be taken to consider human and animal safety because of low clearance. Particular attention must be paid to location of obstructions (posts, pipes, and so on) near the circulation

Figure 12. Stirring fan for improving air distribution. (From Driggers LB: Ventilation of Swine Buildings Using the North Carolina Underslat Ventilation System, AG-132. Raleigh, NC, North Carolina State University Agricultural Extension Service, 1987; with permission. )

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devices, which might deflect air into pen areas and create drafts. The principles discussed earlier should also be considered and implemented, where possible, as the first steps toward improving barn ventilation.

DRAFT CONTROL Drafts and deposits of snow in pens are problems in open-front buildings with a length-to-width ratio of 2.5 or more. These problems tend to occur as wind blows over the roof, around an end wall, or off an adjacent structure such as a silo. Remedies are available if these problems occur. Use of a smoke generator or smoke candles is recommended to determine the exact origin of the draft. When interior drafts are present, they can be modified by constructing solid floor-to-eave partitions at 50-foot intervals (Fig. 13) in buildings over 30 feet wide. When buildings are less than 30 feet wide, the front wall should be closed 16 feet from each end, and solid floor-to-eave partitions should be installed at intervals equal to building width; it is important to either install large summer vent doors in the 16-foot front wall additions or make these sections removable for summer operation. Drafting and snow blow-in sometimes occur through eave vents on the leeward side of both open-front gable roof and monoslope buildings. This is caused by a slight vacuum produced by wind passing over the roof of openfront or open-side buildings, drawing wind and snow back into the building on the open (downwind) side. The problem usually can be alleviated by opening eave vent inlets on the upwind side to offset the vacuum. An additional measure is to install a 2-foot-high solid panel along the top of the open wall just under the eave. Swirl chambers can be used to modify drafts coming around the end wall on the windward side of a building. A swirl chamber is constructed as a 16 X 16 foot section (see Fig. 13) on the windward end of the building. It should be the same height as the open-side or open-front eave and should be built as a porous fence or snow fence. If a lot fence is used on the open building side, it can be offset 16 feet and connected to the building to help form a swirl chamber. Large buildings sometimes tend toward draftiness. When the wind blows against the end of a naturally ventilated building, there tends to be uneven ventilation along the length of the interior, creating drafty conditions. These

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Figure 13. Snow and wind control for open-front sheep and goat buildings. (From Natural Ventilating Systems for Livestock Housing, MWPS-33. Ames, lA, Midwest Plan Service, 1989; with permission.)

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conditions can be modified by making alternating pen partitions solid. In very long buildings, the building can be broken into rooms by installing solid partitions up to eave height at 75-foot intervals. Cold or environmentally modified buildings that have draft problems can often be made more satisfactory by the use of animal hovers. This solution simply involves constructing low-ceiling hovers using plywood or polyethylene sheets at the rear of each pen. In this way, animals have a choice and can move out of the draft if it is uncomfortable. PROTECTION FROM BIRDS AND RODENTS Birds and rodents carry disease and contribute to destruction of building components. Although it is impossible to totally eliminate them from barns, a little care can help discourage damage from their presence. Good rodent control includes a baiting program. Care must be taken to properly store feeds and clean up spillage. Weeds and grass around the building area should be kept mowed. Where practical, insulation should be protected with an inside building liner, including sealing of exposed edges of rigid board insulation. Wall cavities and ceilings should be sealed to discourage rodent access to insulation. Perimeter insulation should be carefully fitted and covered with high-density, fiberglas-reinforced plastic. Ventilation openings must be screened with O.75-inch hardware cloth. Residential window screening should not be used, because it is a major impediment to airHow and quickly becomes blocked with dirt and frozen moisture. Even hardware cloth may require frequent deicing in cold climates to maintain air How. SUMMARY Good ventilation is an important part of any livestock housing system. It may be accomplished by either natural or mechanical means. Generally, except for buildings that must be kept at warm, nonHuctuating temperatures, naturally ventilated cold housing is satisfactory for sheep and goats provided it is dry and draft-free in pen and resting areas, and air exchange is taking place at a rate high enough to remove moisture, gases, and airborne disease organisms from the building. Understanding the importance of site location, building orientation, and principles of ventilation design increases the likelihood of successful barn ventilation. REFERENCES 1. American Society of Heating, Refrigerating, and Air-Conditioning Engineers: Handbook of Fundamentals. New York, ASHRAE, 1985 2. Bodman GR, Jones DD: Nonmechanical ventilation ofMOF swine buildings, PIH-120. In Pork Industry Handbook. West Lafayette, Indiana, Purdue University Cooperative Extension Service, 1985 3. Collins ER Jr: Orienting and Locating Swine Buildings to Minimize Energy Requirements. Publ No. 414-130. Virginia Cooperative Extension Service. Blacksburg, Virginia, Virginia Polytechnic Institute and State University, 1982 4. Driggers LB: Ventilation of Swine Buildings Using the North Carolina Underslat Ventilation System, AG-132. Raleigh, North Carolina State University Agricultural Extension Service, 1987

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5. Jones, DD, Friday WH: Natural Ventilation for Livestock Housing, AE-97. West Lafayette, Indiana, Purdue University Cooperative Extension Service, 1980 6. Jones DD, Friday WH, DeForest SS: Environmental Control for Confinement Livestock Housing, AE-96. West Lafayette, Indiana, Purdue University Cooperative Extension Service, 1980 7. Mechanical Ventilating Systems for Livestock Housing, MWPS-32. Ames, Iowa, Midwest Plan Service, 1990 8. Natural Ventilating Systems for Livestock Housing, MWPS-33. Ames, Iowa, Midwest Plan Service, 1989 9. Sheep Housing and Equipment Handbook, MWPS-3, ed 3. Ames, Iowa, Midwest Plan Service, 1982

Address reprint requests to Eldridge R. Collins, Jr., PhD Department of Agricultural Engineering Virginia Polytechnic Institute and State University Blacksburg, VA 24061

Ventilation of sheep and goat barns.

Good ventilation is an important part of any livestock housing system. It may be accomplished by either natural or mechanical means. Generally, except...
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