The objective of the experiment was to investigate the effect of natural substances as the potential substitute for antibiotics in the boar extender on sperm survival time. Thirteen natural substances were tested. Natural substances were dissolved in 4% DMSO whit a minimum bactericidal effective concentration of between 300 and 4,800 µg/ml. The control sample was diluted with a semen dilution ratio of 1:1 in an APS extender without antibiotics. The sperm survival was assessed according to sperm motility. Sperm motility was evaluated at 0h, 1h and 24h after semen dilution. The sperm motility was significantly decreased over the storage time for all tested natural substances (p < 0.01). The sperm motility after a 24h storage period was only recorded in hydroquinone monomethylether 10 % and Foeniculi aetheroleum 5 %. The results of the present study indicate a negative effect of the concentrations of natural substances added to semen extender on the boar semen survival time. At present, practical utilization of the natural substances we tested as a potential substitute for antibiotics in boar extenders is not possible owing to its reduced sperm motility.