Experiments were done on a pig farm and included about 4850 piglets 24-86 days old and on a broiler chicken farm including about 16000 animals. The possibilities of reducing ammonia and odours by using “deodorase” additives in the feed and in slurry were investigated. Ammonia, hydrogen sulfide as well as other micro-climatic elements have been measured and olfactometric measurements have been done to determine the odour concentration obtained with the use of the additive (165g/t in prestarter feed, 65g/t for the grower and 15g/m3 slurry) compared to a control group. The results showed that for the pigs, the ammonia reduction was about 59% (significant at P<0.001) and the odour reduction was 22% but with no significant difference with the control group. It was found that there were differences in the reduction of ammonia and olfactometric values obtained between the pig and poultry farms (where for poultry the ammonia was reduced by 28% and the odour by 19.7%). No information was given on the economical part of the additive use. The performance regarding odour cannot be considered in this experiment because no significant difference with the use of the additive (the difference of 22% could come from other experimental procedures and not necessarily from the additive). Even if the experiment was done with a large number of pigs, the experiment was not repeated.