The aim of this study was to compare different types of bedding and mucking regimens used in horse stables on the generation of airborne particulate matter <10 μm (PM10) and 3 biogenic gases (carbon dioxide, nitrous oxide, and especially ammonia). Three separate experiments were undertaken. The experiments were carried out in an enclosed stable (9.7 m long, 8.7 m wide, and 3.5 m high) that had 5 single boxes housing 4 horses. The measuring instruments were set up in the middle of one side of the stable. In Exp. 1, 3 types of bedding material (wheat straw, straw pellets, and wood shavings) used for horses were assessed according to their ammonia generation. Each type of bedding was used for 2 wk, with 3 repetitions. The mean ammonia concentrations within the stable were 3.07 ± 0.23 mg/m3 for wheat straw, 4.79 ± 0.23 mg/m3 for straw pellets, and 4.27 ± 0.17 mg/m3 for wood shavings. In Exp. 2, the effects of the mucking regimen on the generation of ammonia and PM10 from wheat straw (the bedding with the least ammonia generation in the previous experiment) were examined using 3 different daily regimens: 1) no mucking out, 2) complete mucking out, and 3) partial mucking out (removing only feces). The mean ammonia concentrations in the stable differed significantly among all 3 mucking regimens (P < 0.05). The greatest values were recorded when the stalls were mucked out completely every day [least squares means (LSM) = 2.25 ± 0.1 mg/m3]. No mucking out resulted in an LSM of 1.92 ± 0.1 mg of ammonia/m3, whereas an LSM of 1.54 ± 0.1 mg of ammonia/m3 was found when the partial mucking out method was used. No mucking out also resulted in significantly less average PM10 (124.4 + 13.4 μg/m3) than in the other 2 regimens (P < 0.05). In Exp. 3, a 6-wk bedding regimen without mucking out was evaluated with regard to gas and airborne particle generation. The ammonia values were found not to increase constantly during the course of the 6-wk period. The average weekly values for PM10 also did not increase constantly but varied between approximately 90 and 140 μg/m. It can be concluded from the particle and gas generation patterns found in the results of all 3 experiments that wheat straw was the most suitable bedding of the 3 types investigated and that mucking out completely on a daily basis should not be undertaken in horse stables. [ABSTRACT FROM AUTHOR]