Effect of Inert Dust Use on the Prevalence of Pulmonary Silicosis in Laying Hens

The poultry red mite (Dermanyssus gallinae) is one of the most significant ectoparasites in poultry production worldwide, causing substantial economic losses and welfare issues. Several approaches are used to control poultry red mites in layer houses, with one common method involving inert dust containing amorphous silica. The aim of the present study was to investigate whether there is a correlation between the use of inert dust and the prevalence of pulmonary silicosis in laying hens. For this purpose, laying hens from Farm A, which used inert dust for antiparasitic control, and Farm B, with similar housing conditions but without inert dust use, were analyzed. Histologic lung preparations, stained with hematoxylin-eosin and periodic acid-Schiff, were examined microscopically for pneumoconiosis in a total of 56 laying hens from each farm. Most of the silica deposits were located peripheral to the parabronchial smooth muscle in the lung. The distribution of pneumoconiosis in Farm A was disseminated in 50 hens (89.29%), multifocal in 5 hens (8.93%), and oligofocal in 1 hen (1.79%) out of 56. The severity of pneumoconiosis was classified as grade 1 in 5 hens (8.93%), grade 2 in 35 hens (62.50%), and grade 3 in 16 hens (28.57%). In Farm B, pneumoconiosis was multifocal in 27 hens (48.21%), oligofocal in 27 hens (48.21%), and unifocal in 2 hens (3.57%). The severity was classified as grade 1 in 55 hens (98.21%) and grade 2 in 1 hen (1.79%). The results showed significantly (p < 0.0001) higher silica deposition in the lungs of hens from Farm A, which used inert dust, than in those from Farm B, which did not use inert dust. Hens from Farm A exhibited increased proliferation of the parabronchial and atrial immune system with higher numbers of macrophages and lymphocytes in areas of silica deposition. Despite this immune response, no fibrosis was detected in hens from Farm A. In conclusion, this study established an association between the use of inert dust in barns and pneumoconiosis in hens housed in these environments. The effects of silica deposition on health and oxygen transport in the lungs require further investigation in long-term inhalation toxicity studies in chickens. Histologic signs of pneumoconiosis developed after relatively short exposure times, highlighting the potential risk posed by these silicate products. The study underscores the need for regulatory approval of silicate-based products to confirm their safety for both animals and humans. Despite the different histologic responses in chickens (no fibrosis), this study suggests that chickens could serve as a sentinel animal model for assessing the human health risks of silica exposure, given their rapid development of lung alterations following exposure.