Houses for intensive poultry production likely contain very high concentrations of airborne contaminants that may negatively affect human and animal health. However, very little is known of the relations between concentrations, size, nature and composition of airborne particles on animal health in intensive livestock housing. Also, mechanisms of responses of animals to unhygienic conditions such as airborne particles, and adaptation responses are unknown. It is likely that animals under high pressure for production such as broiler chickens may be affected severely by continuous antigenic stimulation. Accordingly, the aim of this thesis was to determine effects of airborne dust and its components, and particle size, respectively on the immune system of broilers, and consequently disease resistance and performance (in this case growth). The objectives were to address 1) dust concentrations and particle size distribution present in counts and in mass inside (and around) animal houses; 2) whether dust or its components (with emphasis on pathogen associated molecular patterns or PAMP) affect the immune competence and specific immune response of broilers after challenge via the respiratory tract at different ages; 3) whether broilers may adapt to respiratory challenge with dust and its different components, and particle size; 4) whether dust and its components including particle size affect growth (and heart parameters) of broilers; and finally 5) localization of 1 µm and 10 µm (fluorescent-labelled polystyrene) particles as a model for localization and transport of dust particles in the body of broilers after challenge via the respiratory route
In terms of mass, the dust concentration in poultry houses was generally higher than in pig houses, cattle houses, and mink houses. Mass concentrations of PM10 (particles with aerodynamic diameter smaller than 10 µm) was 0.83 to 4.60 mg m-3 in poultry houses, 0.13 to 1.62 mg m-3 in pigs farms, and 0.02 to 0.12 mg m-3 in cattle and mink farms. In counts, most particles (92%) inside were found smaller than 2.5 µm, whereas these particles only contributed for 2.6% to mass.
Fine dust and coarse dust collected from broiler houses also affected specific antibody responses to a model antigen (HuSA), either declining or enhancing, depending on age of challenge and isotype measured. Components known to be part of dust and with known or expected immunologically mediating features like lipopolysaccharide (LPS), β-glucan, lipoteichoic acid, chitin, NH3, heat-dust, respectively, were used to intratracheally challenge broilers at 3 and 7 weeks of age. Especially LPS and β-glucan enhanced immune responses, but depressed body weight gain of the broilers after primary and secondary challenge. LPS also enhanced antigen-specific responses at various ages, even when administered 4 weeks prior to the antigen. After intratracheal (and also cloacal) challenge, fluorescent-labelled polystyrene beads from two sizes (1 µm and 10 µm) were present in all tissues from the broiler studied during at least one week. Such beads might have been taken up by phagocytic cells or were transferred via the blood stream.
It was concluded that airborne particles in different sizes and with different components could alert the immune system of broilers as exemplified by enhanced primary responses in an antigen- nonspecific fashion. The absence of major effects of dust components on secondary immune responses on the other hand may indicate a regulating role of dust components on the immune system. Dust (components), however, had an important negative impact on body weight gain and heart parameters. It is concluded that there are relationships between hygienic conditions in broiler houses and immune mediated health, and as a consequence likely disease resistance and/or sensitivity to vaccination and other health management procedures. The current study urges further studies on the presence (and identification) and consequences of airborne constituents to protect health of poultry.