A facility for controlled exposure of pigs to airborne dusts and gases

A facility has been developed for a study in which, for 6 weeks, groups of weaner pigs (960 in total) were exposed to controlled concentrations of airborne dust (nominally 0, 2·5, 5 or 10 mg m-3 inhalable fraction) and ammonia (nominally 0, 10, 20 or 40 parts per million, ppm) and the effects on production and respiratory disease measured. The facility comprised five rooms, each holding 24 pigs. Each room was ventilated mechanically at a constant rate of either 30 or 40 air changes per hour in the Winter and Summer, respectively, to minimise the background concentration of pollutants. An artificial pig dust has been developed, though setting the specifications for composition, particle size distribution and microbial content was hampered by the lack of published values for these parameters. The dust was manufactured from feed, barley straw and faeces, mixed by weight in the proportions 0·5:0·1:0·4. The ingredients were oven dried to inactivate microbes and remove moisture and oil binders, milled by a hammer mill and then an air classifier mill, and mixed. This dust was then injected into the supply air of each room via a venturi nozzle fed from an agitated hopper. The size distribution of this dust approximated published values for piggery dust. The dust concentration was monitored with a tribo-electric sensor, which was calibrated against an aerodynamic particle sizer and gravimetric samplers. Ammonia was also injected into the supply air; its rate was controlled with mass flow controllers and its concentration was measured continuously with a NO chemiluminescence gas analyser after catalytic conversion of NH3 to NO at 750 degrees C. The monitoring and control system was controlled by a computer, which included a safety system to terminate pollutant generation if set limits are exceeded. The facility has been used successfully and two batches of pigs have been tested satisfactorily.