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Nine hundred and sixty weaner pigs were exposed for 5 weeks to controlled concentrations of airborne dust and ammonia in a single, multi-factorial experiment. Production and health responses were measured. The treatments were a dust concentration of either 1.3, 2.7, 5.1 or 9.9 mg m-3 (inhalable fraction) and an ammonia concentration of either 0.7, 10.0, 18.8 or 37.0 ppm, which are representative of commercial conditions. The experiment was carried out over 2 years and pigs were used in eight batches, each comprising five lots of 24 pigs. Each treatment combination was replicated once and an additional control group (nominally 0 mg m-3 dust and 0 ppm ammonia) was included in each batch to provide a baseline. For the other four lots in each batch, the dust concentration was common while all four ammonia concentrations were used; thus the split-plot design was more sensitive to the effects of ammonia than dust.

The pigs were kept in a purpose-built facility. The pollutants were injected continuously into the air supply. An artificial 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, milled and mixed and then resuspended in the supply air. Dust concentration was monitored with a tribo-electric sensor, which was calibrated against a TSI aerodynamic particle sizer and gravimetric samplers. Ammonia was supplied under pressure from a bottle bank and its concentration was measured with a NOx chemiluminescent gas analyser after catalytic conversion.

Liveweight gain and food intake were measured after 2 and 5 weeks of exposure. Exposure to both aerial pollutants depressed performance by an amount dependent upon dust but not ammonia concentration. Both food intake and liveweight gain, but not food conversion efficiency, were lower for weaner pigs exposed to 5.1 and 9.9 mg m-3 dust concentration compared with control and 2.5 mg m-3 treatments.