Abstract The following paper contains a mathematical model for the analysis of temporal variations of a chamois (Rupicapra rupicapra L.)-Trichostrongylidae free-living system in the Brenta area (Trentino, Italy) under different harvesting regimes. The numerical values of the parameters of the model were obtained through the analysis of population counts and the parasitological surveys obtained during a four year study. Different harvesting regimes could affect differently the dynamics both of the host population and its parasites. Simple demographic analysis seems to suggest that the culling of older individuals is appropriate. However, if we insert a parameter into the system which considers immunity to parasitic infection then the culling of younger individuals becomes more appropriate for the maintenance of health and population size.