Cross-contamination of feed with antibiotics are possibly not desirable slectiedruk for antibiotic resistance. However, there is little to no literature is available regarding the effect of low doses of antibiotic resistance selection. The main question is whether these low doses have an effect on increasing the selection of resistant bacteria in the gut and the transfer of resistance among bacteria. The answers will contribute to this on the following questions: 1. The resistance selection is mainly expected at the level of the intestine. Hence, in the first place is to determine the concentration of the particular antibiotic is at a carry-over of 3% in the intestine. 2. A second major question is whether all the germs for the resistance selection as well as genes is the same size for the different resistance increases the transfer of resistance genes between bacteria. 3. Finally, on the basis of a risk assessment model, and based on the obtained data in the different studies have examined the impact of the carry-on the resistenieontwikkeling on animal population level.