SIMULATED CATTLE FEVER TICK INFESTATIONS IN ROTATIONAL GRAZING SYSTEMS

Prior simulation analysis of cattle fever tick population dynamics has indicated that fixed rotation, short duration grazing (SDG) systems c ould mediate the spread of ticks among pastures if rest periods were g reater than 100 to 150 days. A question arose whether variable rotatio ns with rest periods approaching 35-70 days could mediate the spread o f ticks within these rapid, rotational grazing systems. An 8-pasture:l -herd extensive (26-34 days:182-238 days graze:rest) and intensive (5- 10 days: 35-70 days graze:rest) short duration grazing system was simu lated over a 2-year period after a spring and fall introduction of inf ested animals using a model depicting both temporal and spatial proces ses involved in host-parasite-landscape interactions. The extensive SD G system was infested for 639 and 424 days for spring and fall introdu ctions, respectively, The intensive SDG system was continuously infest ed throughout the 24-month simulation. Although the intensive SDG syst em was continuously reinfested, there were more frequent tick-free per iods in the fall introduction than the spring introduction, These simu lations indicate that rest periods exceeding 150 days are necessary to minimize the rate and extent of spread of ticks in variable rotationa l grazing systems. These considerations are pertinent to the goals of both control and eradication strategies.