If you are concerned about making the most productive, least stressful indoor environment for pigs, you need a strategy for benchmarking your building’s performance. This goes beyond measuring the dry-bulb air temperature. Even though many factors can carry the “environmental” label, such as drinking water quality, flow rate and access, air contaminants, flooring and floor space, feeder configuration and adjustments, I want to focus on thermal-comfort factors.
Thermal-comfort factors change with the pig’s body size and production stage, but the basics are largely measurable. They include dry-bulb air temperature, surface temperatures, relative humidity and air speed. The difference in air pressure between the room and outdoors also is important and easy to measure in mechanically ventilated rooms.
Ventilation-system controls are much better today than those made a few years ago. However, controller performance is still often based on air temperature recorded in one or two places in a room. More importantly, the sensors are seldom placed near the pig’s level. Mechanisms involved in heat loss from the pig, such as conduction to or from the floor, convection to or from the air, radiation to or from surrounding surfaces and evaporation from the pig’s lungs and skin, are not measured at all.
Contractors build the structure, measure air temperature and sometimes the relative humidity, then make assumptions about the pig’s comfort based on building’s design.
What if the structure is modified, the controlled ventilation system is malfunctioning or some aspect of the building is not properly maintained? Then some or all of the assumptions are compromised, and the sensor’s air-temperature reading alone cannot tell you whether the building is comfortable for the pigs. You cannot rely on the installed air-temperature sensor readings alone; you need additional measurements.
So, where do you start? Air temperature and relative humidity are easy and economical to monitor using miniature data loggers. You can get started with a couple of basic loggers and software for about $250. Place a few of these units in a room and leave them for a few days at a time. Set the data loggers to collect temperature and relative-humidity data every five minutes or so from two or three locations in the building. Use your desktop computer to examine the data to see how much variation occurs within the building and throughout the day. It’s important to do this for each season of the year.
From the data, you can determine whether the ventilation system is actually maintaining the building temperature near your desired set-points, and if there are problem areas in the space. The winter data will illustrate whether you have adequate fresh ventilation air entering the building. High relative humidity (greater than 75 percent) usually implies inadequate air exchange.
The next thing to consider is air speed at pig level. Young pigs are especially susceptible to drafts, so you need to measure air speeds at a few places within the building. You want air speeds around 30 feet per minute or less — that’s one-half foot per second. The most reliable way to measure this is by putting something visible in the air stream. I like to use seed “parachutes” from the dried seed pods of common milkweed. You can estimate the air speed near the pigs by clocking the milkweed fluff’s travel speed. For example, if it travels more than 6 inches sideways in a second, the air current will feel like a draft to a baby pig. Monitor and record the results for each season.
Finally, consider investing in a hand-held infrared surface-temperature thermometer. Use it to scan the inside of the room to find the hot surfaces in the summer and cold surfaces in the winter that may indicate poor insulation. Those surfaces can contribute to pigs overheating in summer or being chilled in winter. You can buy a decent infrared surface-temperature thermometer for about $150.
Editor’s note: For more information on livestock building ventilation, go to the Midwest Planning Service Web site at www.mwps.org.