Measuring Air Quality in Rabbitry
"People manage the things that they measure.", says Dr. Temple Grandin, animal behaviourist from Colorado. I believe her idea applies to many things including air quality in the rabbitry. During the winter, air quality can really deteriorate in a barn. In an effort to keep the barn warm, the amount of dry fresh air entering the barn tends to be greatly reduced. Fans are turned off and vents closed down. We check the air quality in our barn using our noses. It has been shown that our sniffers become desensitized with long term exposure to waste gases found in barns. Everyone has a different opinion on how "bad" the air is in a barn.
I asked former OMAFRA ventilation engineer, Harry Huffman, for some pointers on air quality and ways to measure that quality in rabbitries. The most important gases to measure are ammonia (NH3) and carbon dioxide (CO2). The ammonia level should be kept below 20 ppm (parts per million) and he prefers to see it below 15 ppm. If the ammonia level goes above 20 ppm it can negatively affect you and your rabbits. In the winter time, Harry recommends four air changes per hour(AC/hr) in a barn with a high ammonia level. In the summer, intensive operations need to greatly increase the ventilation rate to relieve the build up of heat. Carbon dioxide levels in outside air measure from 300 to 350 ppm. In a barn Harry finds acceptable levels range from 2500 ppm to 5000 ppm.
How do you measure ammonia and carbon dioxide levels? Safety supply stores sell pumps and diffusion tubes. I phoned a store and was told the pump costs $321 and tubes come ten in a pack costing $47.05 / pack. You might want to share the cost of a pump with friends. An alternative to the pump-tube combination is the passive dositube. Agviro Inc. of Guelph (email@example.com) sell boxes of ten passive diffusion tubes for $63.00/box. Agviro says the Sensidyne passive diffusion tube does not require a pump. The end of the tube is broken off and the tube is hung in the barn for several hours. Contaminated air diffuses into the tube and creates a colour change. A colour chart with ppm scale is compared to the colour stain in the tube.
How do you measure Air changes per hour? First you must know the capacity of your exhaust fan. Usually capacity is rated in cubic feet per minute (cfm). Check to see if the fan runs continuously or not. Measure the room's volume in the same units as fan capacity (cf). Plug these two figures into the following formula :
60 min/hr X Fan Capacity in cfm = AC/hr
Room Volume in cf
Example: A barn measures 100 ft X 30 ft X 8 ft = 24,000 cf = Room Volume
Fan Capacity 1000cfm and the fan runs continuously . 60 X 1000/24,000 = 2.5 AC/hr
Air movement. Not just the number of air changes per hour is important, but the movement or circulation of that fresh air is also critical. If the barn has poorly functioning air inlets there may be "dead spots" of air in your barn. This could mean some animals have a much poorer quality of air around them than measured elsewhere in the barn. Smoke pencils can be used to identify these dead spots of air.
Relative Humidity. Relative humidity (RH) must not climb to high levels in the rabbitry; it should remain between 50 to 65%. Traditionally, other classes of livestock are comfortable and healthy with a maximum level of 75 to 80% RH. There is a selection of instruments for measuring relative humidity. These may be purchased from scientific supply stores.
Production records may help to gauge the effects of poor air quality in your rabbitry. Don't let air quality hurt your animals' quality of life and your bottom line.
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