Biochar in bedding for loose housed laying hens - for the improvement of work and animal environment The aim of this project was to study how the ambient air environment in barns for loose housed laying hens is affected by mixing biochar into the bedding. The objectives were to investigate the bedding’s effect on the ammonia and the dust/particulate matter (PM) concentrations. Studies were performed by laboratory studies and by field trials in aviaries with loose housed laying hens. In the lab study, dust formation was tested by tumbling (stirring) three different types of biochar and one product of wood shavings. Wood shavings were used as a control/comparative bedding material, as it is the most common source of litter in Swedish laying hen flocks. The dust formation was higher for biochar compared to the wood shavings. Additionally, a higher dry matter content in the biochar resulted in higher dust concentrations. Presumably, this is because biochar is a porous material, which easily falls apart during mechanical processing. In practice, the mechanical processing will supposedly not be so forcefully because of e.g., the hens pecking in the bedding. However, it might be an aspect to consider during some work tasks, e.g., removal of the bedding. During the field trials, data of ammonia concentrations and PM were collected in four aviaries with 100 loose housed laying hens per aviary. Each aviary was provided with different mixtures of bedding material. The mixtures were 1) wood shavings and a bacteria/fungi additive, 2) only wood shavings, 3) wood shavings and biochar, and 4) peat or peat mixture (80% peat and 20% wood shavings). The measurements of ammonia were collected with a hand-held aspirator pump, one sample above the slatted flooring and two samples above the bedded flooring. No differences of the ammonia concentrations were obtained in the different aviaries, bedding materials and flooring. Differences in ammonia concentrations were not assumed above the slatted flooring, but above the bedded flooring. In future studies, continuous measurements and more data sampling would be relevant to analyze, to compare differences in the ammonia concentrations, depending on the bedding material, and correlate it to the time of day, the behavior/activity level of the laying hens, etc. The fractions of PM measured during the field trials were PM1, PM2.5, PM4, PM10 and total-PM. In each of the four aviaries, approximately 500 samples were taken with a laser photometer. The results were slightly different compared to the laboratory study. For all the PM fractions, the PM concentrations were highest in the bedding with only wood shavings. An influencing factor may be the dry matter content of the bedding materials, 90% for wood shavings and 70% for biochar. Another aspect is the laying hens’ activation and encouragement to process the bed by pecking, dust bathing etc. Both the laying hens and the eggs, in the aviary with biochar, appeared to have a greyish color at times. This study shows that the dry matter content of bedding materials is important for the dust/PM concentrations in the ambient air in animal production facilities. How different biochar with different properties, e.g. dry matter content and size fractions, affect the behavior of the laying hens (encouragement to process the bedding) is a topic for future research. One conclusion is that different biochar may have very different properties and that these varying properties can have quite different effects on the behavior of the laying hens, animal environment and work environment.