Good air quality leads to healthy animals and productive animal facilities. When we evaluate air quality in livestock housing, what do we want to determine? What makes one indoor animal environment better than another? Instruments allow us to objectively evaluate and quantify environmental parameters. Instrument readings then can be compared to recommended environmental levels. The second part of this series of three fact sheets, Instruments for Measuring Air Quality, describes types of instruments and how to take proper measurements.
An evaluation of indoor air quality must emphasize the animal perspective, which is not necessarily the same environment in which a human would feel comfortable. Air quality characteristics are most important in the zone where the animal is confined.
Animal health and comfort must be the primary concern in livestock facilities. After all, animals often remain in that environment all day, while workers only visit periodically for chores and inspection. The comfort of humans working in the facility should not be disregarded, but it can be effectively controlled by means such as clothing rather than by keeping the whole environment adjusted to human standards. Temperature seems to be the main environmental difference between livestock and human comfort zones. In general, the comfort zones for adult livestock are cooler than the human comfort zone. Dust and air contaminant levels that provide acceptable air quality for animals are not always reasonable for humans, or protective breathing masks may be necessary for human safety and comfort. Additional building concerns, such as keeping temperatures above freezing, usually can be accommodated while maintaining an adequate animal environment.
Commonly-measured air quality characteristics related to animal comfort include temperature, humidity, and air speed. These are easily measured and roughly characterize the animal environment. Contaminant gases or dust also are important. The temperature of walls and floors will affect animal comfort, as will cold air drafts. Effective environmental temperature accounts for the combination of air and surrounding building surface temperatures plus the effect of air moving over the animals.
We also should evaluate the ventilation system, which is responsible for many major aspects of indoor air quality. This is the topic of the third fact sheet in this series, Evaluating Mechanical Ventilation Systems. System characteristics, such as air speed through fans, pressure differences the fans operate against, and air speed at inlet openings, are easily measured. However, instruments must be used properly to obtain values that truly represent the system. Air flow visualization is a useful tool to evaluate environmental conditions and the ventilation system's air distribution.
1. Measure the right thing. Measure characteristics of air the animals are breathing and/or the air blowing over their bodies. If cow comfort is the issue, get in with the cows and measure the air quality in their zone. Get down to the level of the pigs nose. Go into the sleeping areas of penned animals and within, or at least between, the cages of layer hens. Air characteristics such as temperature, humidity, and particularly levels of contaminant gases such as ammonia, can vary greatly within a livestock confinement zone. Compare measurements taken in resting, eating, and manure handling areas.
2. What is the instrument measuring? The instrument can only read what it is exposed to. Be aware of what part of the instrument senses conditions. Exposing an instrument to an environment alters the environment immediately adjacent to the instrument. Positioning an air velocity meter in the jet of air exiting a fan disturbs the air, forcing it to go around the meter. The measured velocity represents a disturbed air flow, yet this effect cannot be completely avoided. A human positioning and reading the meter while standing in the air jet exiting a fan adds a very large human obstruction to the disturbance created by the meter. This obstructed air velocity measurement will not be indicative of air flow normally exiting the fan. Similarly, a temperature probe positioned in direct sunlight will indicate a higher temperature than a probe positioned more appropriately under cover. Decide what it is that you want to measure and position the instrument to most appropriately measure that quantity.
3. Understand how your instrument works. By understanding basic principles of how the instrument detects air characteristics, you can troubleshoot the instrument when curious readings are obtained or when adjustments and calibrations are needed. A number is only as good as the understanding that went into determining it. For sensitive instruments, how do you know if fluctuating readings are a natural part of the air you are trying to characterize or part of the instrument's measuring mechanism? How long does it take the instrument to determine and display a stabilized reading? Livestock housing is too dusty, humid, or dirty for some instruments to work properly. For example, instruments that measure humidity by the expansion and contraction of fibers as humidity changes are unreliable in livestock settings. Some instruments may work well for a while in livestock buildings, but then go out of calibration. You need to be able to diagnose such problems.
4. Question each reading. Does the reading make sense in the environment being considered? Take more than one reading. A set of three readings often is necessary to confirm that sporadic measurements are reliable. Air velocity measurements, due to gusty conditions, may never settle down into one distinct reading, so a range of readings should be averaged.
5. Record your readings and observations. Summarize the results. Is there a pattern? Do measured conditions correspond to an observed or perceived problem? Be sure to include conditions which affect the enclosed animal environment, such as outside weather conditions, livestock density, management practices, behavior, etc. Environmental conditions change during the day. It may be necessary to use a recording instrument, maximum-minimum instrument or simply more than one "reading session" to correctly characterize an environment.
Once measurements are taken, the numbers should be compared to desirable conditions. Improvements to environmental quality can then be pursued with more certainty about current conditions and future achievements.
Desirable air quality characteristics depend on animal species and age. Within livestock housing, a range of temperature and humidity levels are acceptable. Contaminant gases and dust levels need to be kept below a threshold. For young animals, air speed is kept below a certain level to avoid chilling, while for adult livestock, during hot weather, there will be a minimum desired airspeed for cooling effect. These recommended air quality characteristics are the goals for a productive animal environment. With instruments, we can evaluate current conditions and after an analysis, make recommendations for improvement.