Research Paper Does rearing system (conventional vs. organic) affect ammonia emissions during the growing and fattening periods of pigs? Marko Ocepek a,b,* , Dejan  Skorjanc a a University of Maribor, Faculty of Agriculture and Life Sciences, Pivola 10, Ho ce, Slovenia b Norwegian University of Life Sciences, Department of Animal and Aquacultural Sciences, P.O. Box 5003,  As, Norway article info Article history: Received 30 December 2015 Received in revised form 2 April 2016 Accepted 7 April 2016 Keywords: Pigs Rearing system Growth performance Excreting behaviour Ammonia emission Ammonia emissions from organic (ORG) and conventional (CON) rearing systems in rela- tion to pig growth rate and behaviour were studied. Microclimatic conditions and ammonia concentrations were monitored. Excretory behaviour was recorded in the growing and fattening periods using video cameras. Throughout the experiment, significantly lower ammonia emission was detected in facilities of the ORG pigs (P < 0.001). The differences in ammonia emission may be partially explained as a consequence of lower level of crude protein, lower feed intake and different growth performance of ORG pigs. Urination and defecation indoor (on the slatted and solid floors) were higher in the CON group (P < 0.05). The results of the present study show that the minimum requirements specified in organic legislation are well suited to normal pig excretory behaviour in both growing and fattening stages and provides pigs cleaner indoor space as well as an improved environment for human and pigs, with around 40% of reduced ammonia emission. © 2016 IAgrE. Published by Elsevier Ltd. All rights reserved. 1. Introduction The housing standards for organic pig production are based on creating an environment in which the animals can ex- press their natural behaviour, ensuring a high welfare stan- dard (EC, 889/2008). Organic standards are higher than conventional standards for housing, nutrition, breeding and veterinary management. Changes in housing conditions such as floor type, space allowance, and access to an outdoor area, as well as in diets that do not use synthetic amino acids and growth promoters, could affect pig performance and carcass and meat quality (Lebret, 2008). Therefore, it has been suggested that performance and carcass and meat quality of pigs reared under organic conditions could be the same (Hansen, Claudi-Magnussen, Jensen, & Andersen, 2006; Millet, Hesta, & Seynaeve, 2004), or even better, than pigs from conventional rearing systems (Oksbjerg, Strudsholm, Lindahl, & Hermansen, 2005; Olsson, Andersson, Hansson, * Corresponding author. Norwegian University of Life Sciences, Department of Animal and Aquacultural Sciences, P.O. Box 5003,  As, Norway. E-mail address: marko.ocepek@nmbu.no (M. Ocepek). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/issn/15375110 biosystems engineering 147 (2016) 81 e89 http://dx.doi.org/10.1016/j.biosystemseng.2016.04.002 1537-5110/© 2016 IAgrE. Published by Elsevier Ltd. All rights reserved.