EN
The research was carried out on 24 Californian breed rabbits, aged 12 weeks, weighing between 1.8 and 2.2 kg, from which the caecum content were taken and placed in fermentation in vitro. 0.15 ml of toltrazuril was added to the content in the vessels (the experimental group), which resulted in the final concentration of 25 ppm of toltrazuril in the vessel. In the analyses of gases obtained during fermentation it was determined that CO₂ had the most substantial percentage, above 70%, CH₄ had a smaller percentage of 15% of the gases produced in the caecum content, while hydrogen and hydrogen sulphide had the least considerable portion of it. During the fermentation the amount of the gases produced changed and the zenith of fermentation took place between the second and fourth hour of incubation. The addition of toltrazuril to the caecum content of a rabbit leads to an increase in the value of CO₂:CH₄ not observed in the control experiments. The addition of toltrazuril causes the increase in the hydrogen level which may result from changes in either the composition or activity of bacteria releasing H₂.