Dropping night-time temperatures bring with them the need for reduced ventilation in swine barns. This becomes a day-long need when winter arrives, and with it a need for increased awareness of the effect that reduced ventilation can have on pollutant burdens for the animals and the stockperson in the barn. Excessive pollutant burdens can affect animal productivity as well as human health.
The substances that contaminate animal facilities are the consequences of animal production: particles from feed, skin and building materials, gases from metabolism of the animals and microbes that live in and around them, and indeed the microbes themselves from various sources. In reviewing the possible sources of particulate contaminants, researchers have listed every conceivable source down to the attrition of wooden or concrete building materials. No possible source has been overlooked. As well, every possible influence on the concentration of pollutants has been listed; animal activity, air temperature, relative humidity, ventilation rate, stocking density and volume of air space per animal, feed type and feeding method, type and composition of litter. Each of these could conceivably, in certain situations, be the important factor in a problem environment. There are also many potential interactions between these factors.
“Dust” may refer to any fine particles including liquid droplets as in mists. Generally, however, it means solid particulates small enough to be easily put into suspension in the air and remain suspended for a significant period. To some extent, any material may degrade to fine particles that may become dust, and this accounts for the mix of dust found in livestock facilities. There are two major fractions of interest. The inspirable fraction, often confused with “total” dust, represents that fraction which is likely to be inspired by a human during normal breathing. The respirable fraction represents that fraction which is likely to be carried to the respiratory region of the lungs and so is potentially hazardous to health. The distribution of particles into these fractions depends on the speed of air during inspiration, the aerodynamic characteristics of the dust particles, and the efficiency of particle trapping in the upper respiratory tract.
The nature of dust
The dust in a pig house will have many sources and so will consist of many substances and, by the nature of the processes that produce it and affect it afterwards, can be of any number of shapes and sizes. Particles that are large enough to settle out quickly will only be an aerial contaminant for a short period. During feeding or the addition of bedding, however, dust can be in very high concentration. Most of the particles in swine barn dust are in the respirable size range, although on a mass basis the respirable fraction may be small. Studies using microscopy and chemical analysis have found that the dust in pig buildings is predominately feed (on a mass basis). The respirable particles have been found to be mainly faecal material, while larger particles were mainly feed. Livestock environments are rich with micro-organisms, and airborne particles are important carriers of microbes.
Although efforts are being made to find waysto reduce dust in swine barns, for the time being they are an unavoidable fact of life. Considering the composition of swine barn dust and the concentrations that swine workers may be exposed to, it is important to protect worker health through the use of masks. This is particularly important during long periods of exposure and during winter when dust levels are probably at their worst.