The effects of individual and combinations of airborne pollutants on feed intake, immune function and physiology of the pig.

Abstract

Poor air quality and surface hygiene are associated with increases in the prevalence and severity of enteric and respiratory diseases, as well as reduced growth rates in pigs. The pollutants which contribute to poor air quality include gases, dust, airborne particles, microorganisms and their toxins. In this study I investigated; 1) the effects of ammonia and alpha haemolytic cocci (AHC) including viridans-group streptococci (VGS) on feed intake, immune function and respiratory tract physiology in pigs, 2) the effects of stocking density on air quality parameters and growth rate in pigs and 3) the effects of shed design and management on air quality parameters. While exposure to AHC appeared to have a greater effect than ammonia on growth rate and feed efficiency, as well as aspects of immune function, the most significant effects were observed in pigs exposed to high levels of ammonia followed by AHC. There was a strong positive relationship between the stocking density (StD) (m³ airspace/pig) and the mean growth rate in pigs from 10 to 22 weeks of age, in an allin/all-out (AIAO) system. There was also a strong negative relationship between stocking density and the number of viable bacteria in the airspace. As the volume (m³ of airspace)/pig increased, the concentration of bacteria in the airspace decreased and the growth rate of the pigs increased significantly. I hypothesise that airborne bacteria trigger an immunological challenge which redirects metabolic activity that would otherwise contribute to growth and skeletal muscle accretion. There is evidence that shed design and management can affect air quality and, consequently, growth rate of pigs. The results indicate that improving ventilation through widening ridge vents, leaving floors to dry before restocking pens, increasing pit depth to ≥400 mm, and flushing pits with fresh water all have a positive effect on air quality and growth rate. It is clear that facilities need to be managed as an all-in/all-out (AIAO) system as this enables farmers to maximise hygiene by thoroughly cleaning pens between batches, which is likely to improve air quality. Other important management and husbandry factors include adhering to stocking density (m³ airspace/pig) and stocking rate (pigs/m² floorspace) recommendations, especially in naturally ventilated buildings. The shape and dimensions of the shed, the ventilation and heating system used, and the effluent management system are also important. Maintaining good air quality is essential for pig health, growth, and welfare, as well as those working with pigs.