Environmental Management in Confinement Systems
The Basics of Environmental Management in Confinement Systems
Published: October 19, 2012
By: Dr. Mike Brumm, owner of Brumm Swine Consultancy, Inc
As a homeothermic species, the pig maintains a relatively constant core body temperature. When raised in pens with outside access, it aggressively modifies its behavior in response to changing climatic conditions. If conditions are such that it risks losing body heat it seeks shelter, huddle with other pigs, burrow in materials such as small grain straw, eat more feed for increased metabolic heat production, etc. If conditions threaten to elevate body temperature it seeks shade, reduces feed intake in an attempt to reduce metabolic heat production, reduces activity and seeks water sources such as wallows for evaporative cooling.
Generally pigs grown in pens with outside access and variable temperatures have lower performance and poorer feed conversion efficiencies than pigs grown in indoor or confinement facilities. It is expected that pigs in confinement facilities will have minimal if any cold stress. In theory it should also be easier for producers to modify the physical environment to minimize decreases in performance due to summer heat. The ventilation system (fans, inlets, controllers, heaters, louvers, curtains, etc) is the means by which the pig's environment is modified to keep moisture, gases and heat within the ranges desired for growing pigs in confinement facilities.
The ventilation system can be either natural or nonmechanical (sidewall openings and chimney exhaust or ridge opening designs) or mechanical (fans for creation of static pressure differentials between inside and outside).
Non-mechanical ventilation systems have the advantage of low operating and investment costs. However, their operation is dependent on outside conditions, on thermal buoyancy (hot air rises) and predominantly on wind velocity and direction and thus often require more adjustment to maintain conditions in the pig's thermoneutral zone. If the system depends primarily on air velocity (wind) for optimal performance in summer heat there will be times when heat removal from the confinement facility is not adequate.
In North America the trend has been towards mechanical ventilation systems or a hybrid or blend of both mechanical and non-mechanical systems. Almost all confinement barns now use some form of mechanical ventilation in cold weather. This allows for more consistent control of moisture levels in the facility, minimizes temperature fluctuations that would be below the pig's thermoneutral zone and generally conserves fuel used to heat the animal zone in cold weather.
The goal of mechanical ventilation in cold weather is to remove the moisture in the air that is the product of the pig's metabolism and moisture from pig activities that results in wet pen surfaces. In addition, it keeps carbon dioxide levels below the 5000 ppm upper limit and dilutes any gases that are the product of manure decomposition.
The recommended minimum ventilation rates for moisture control in confinement facilities are given in Table 1. In general these rates have proven to be adequate for oxygen and carbon dioxide needs. If manure is stored inside the facility and anaerobic decomposition occurs, odor levels (especially ammonia) may be higher than desired at the minimum rates, especially in weaned pig facilities.
The goal of summer or hot weather ventilation is to hold room air temperature to within a few degrees of outside temperatures and to provide high velocities in the pig zone (at least 300 feet or 1.5 meters per second) to maximize convective heat loss. A major challenge for summer ventilation is the recognition that because growing pigs are adding heat to the air as it passes thru the facility, the best one can do with ventilation is to "cool" or keep the pig facility to within 1-2C (2-4F) of outside air temperatures.
A common mistake often made by producers is to assume that insulation is only needed in swine facilities in cold climates. In cold climates the use of insulation on walls and ceilings/roofs of production facilities limits heat loss from the facility. It also results in warmer interior surface temperatures which reduce radiant heat loss by pigs and minimizes condensation problems in the facility.
Insulation is rated according to its ability to resist the flow of heat. In the US this is commonly referred to as the 'R' value with higher values being more resistant to heat flow. Another common method used to express the resistance to heat flow is the 'U' value which is the overall coefficient of heat transmission. The U value is 1/R (MWPS, 1977).
For production facilities constructed near Des Moines, Iowa, the recommended amount of ceiling insulation is R25-R30. For sidewalls a minimum of R5 is recommended to minimize condensation on interior surfaces. These values are appropriate in a climate zone where the average low temperature in January is 14F (-10C) and the average high temperature in July is 86F (30C) with extremes of -20F (-29C) to 100F (38C) common most years (www.weather.com). These winter and summer ranges compare to average lows of 5C (41F) in July and highs of 31C (88F) in January for Córdoba, Argentina.
Insulation of the building during warm weather, especially in ceilings and/or roofs, limits solar radiation heat transfer. While insulation levels don't have to be as high as for cold weather, they still need to be large enough to modify the rate of heat infiltration into the facility. For climates in the US similar to that of the major pork production regions of Argentina, it is generally recommended that ceiling/roofs have a minimum insulation of R12 (MWPS, 1977).
A majority of the time, environmental management in pig confinement facilities throughout the world is based on the need for heat removal. Growing pigs produce tremendous amounts of heat and the evidence suggests heat production from growing pigs increases about 12-15% every 10 years due to improvements in the rate of lean deposition (Brown-Brandl et al, 2004). Figure 1 depicts the total heat production (sensible plus latent) for different pig weights and this author's estimate of current levels of heat production.
Heat production by lactating females has also increased as the level of milk production by these females has increased in response to genetic progress and nutritional improvements (Pedersen, 2002). A 200 kg sow housed at 22C produces 1500 Btu/hr (440 W) of heat in the later phases of lactation. Of this total heat production, 911 Btu is sensible heat and 589 Btu is latent heat.
Because heat production has increased due to improved pig productivity, the impact of excessive heat in confinement buildings is even more pronounced. For example, Huynh et al (2004) concluded that the upper critical temperature for 60 kg growing pigs is somewhere between 21.3 and 22.4C for respiration rate and between 22.9 and 25.5 C for feed intake. Nienaber et al (1997) have suggested that the upper critical temperature threshold declines rapidly when pigs weigh more than 75 kg. They further suggest that pigs with high rates of lean gain (such as today's genetics) are much more sensitive to high temperatures than pigs with medium rates of lean gain. This conclusion was supported by the results of Renaudeau et al (2011).
All of this discussion suggests that heat management is a very critical issue for producers with confinement facilities. Pigs have 4 methods of gaining/loosing heat:
1. Conduction – the transfer of heat by contact with a surface. This method is a concern in farrowing crate creep areas when materials such as metal flooring may conduct heat away from the new born pig.2. Convection – the transfer of heat by contact with a fluid (such as air or water) that is at a different temperature than the pig. This is typically thought of as 'drafts' when the result is a chilled pig and as cooling when it removes heat from a warm pig. Convective cooling is generally maximized at air speeds of approximately 1.6 m/s. Increasing air velocities in the pig zone faster than this have not been demonstrated to improve cooling. Cooling by convection is only effective when air temperatures are below the surface temperature of the pig or approximately 35C. If air warmer than this is blown across the skin of the pig the pig's core body temperature will increase.3. Radiation – the transfer of heat to a surface without direct contact. Most producers are familiar with this as solar heating. In production facilities, if the roof or ceiling is not insulated this can become a source of significant heat gain in the pig space. The greater the temperature difference between the building surface and the pigs' skin temperature (either hot or cold), the greater the heat gain or loss by the pig.4. Evaporation – the transfer of heat by the change of water from a liquid to a vapor. Each 454 g of water in the air as water vapor represents 1044 Btu (306 W) of heat.
Successful environmental management for heat stress involves both air movement (convection) and the addition of water for evaporation. In grow-finish facilities it is generally recommended that fans should begin blowing across the surface of the pig at 7-8C above the set point temperatures of Table 2.
At 10C above the set point evaporative cooling should begin. In general, the skin of the pig is made wet using relatively large droplet nozzles. As soon as the skin is thoroughly wet, the water is shut off and the pig cools by drying. Generally this drying period lasts 15-20 minutes and then the pigs are once again made wet.
Recognize that little cooling occurs during the wetting of the pig as the blood vessels vaso-constrict, especially if the water is cool (15-20C). In general nozzles for wetting pigs are sized such that sufficient water can be applied to the pig for thorough wetting in less than 2 minutes. Then a 15-20 minute period of drying occurs before the pig is re-wetted. Air flow over the pig at speeds up to 1.6 m/s can enhance this drying. Nozzles are sized and located such that no more than 60% of the pen area is wet. This allows individual pigs that may be ill to avoid getting wet and cooled and keeps water from drifting into feeders, etc.
References
Brown-Brandl, TM, JA Nienaber, H Xin and RS Gates. 2004. A literature review of swine heat production. Trans ASAE 47(1):259-270.
Harmon, J, H Xin and J Shao. 1997. Energetics of segregated early weaned pigs. Trans ASAE 40:1693-1698.
Huynh, TTT, AJA Aarnink, MWA Verstegen, WJJ Gerrits, MJH Heetkamp and B Kemp. 2004. Pigs' physiological responses at different relative humidities and increasing temperatures. Paper 044033, Amer. Soc. Ag. Eng., St Joseph, MI
MWPS. 1977. Structures and Environment Handbook. MWPS-1, Midwest Plan Service, Iowa State University, Ames.
MWPS. 1990. Mechanical ventilating systems for livestock housing. MWPS-32. Midwest Plan Service, Iowa State University, Ames.
Nienabler, JA, GL Hahn and RA Eigenberg. 1007. Development of an upper temperature threshold for livestock. Paper 974010, Amer. Soc. Ag. Eng., St Joseph, MI
Pedersen, S. 2002. Heat and moisture production for pigs on animal and house level. Paper 024178, Amer. Soc. Ag. Eng., St Joseph, MI.
Renaudeau, D, JL Gourdine, and NR St-Pierre. 2011. A meta-analysis of the effects of high ambient temperature on growth performance of growing-finishing pigs. J. Anim. Sci. 89:2220-2230
Zhang. 1994. Swine building ventilation: a guide for confinement housing in cold climates. Prairie Swine Centre, Saskatoon, SK, Canada
Table 1. Recommended minimum and maximum ventilation rates for confinement facilities. Hot weather rates modified from MWPS, 1990.
Table 2. Recommended room temperatures for pigs on fully slatted floors at pig level. At facility temperatures higher than these set points, ventilation rates increase for heat removal. At temperatures below these set points facility modifications such as heat additions are necessary for pig comfort. Adapted from Zhang (1994).
Figure 1. Estimated total heat production by growing pigs, sensible plus latent heat. Adapted from Brown-Brandl et al (2004).
This paper was presented at the XI National Congress of Swine Production (CNPP), Salta, Argentina, August 14-17, 2012.
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Brumm Swine Consultancy, Inc.
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