Simulated cattle fever tick infestations in rotational grazing systems.

Abstract

Prior simulation analysis of cattle fever tick population dynamics has indicated that fixed rotation, short duration grazing (SDG) systems could mediate the spread of ticks among pastures if rest periods were greater than 100 to 150 days. A question arose whether variable rotations with rest periods approaching 35-70 days could mediate the spread of ticks within these rapid, rotational grazing systems. An 8-pasture:1-herd extensive (26-34 days:l82-238 days graze:rest) and intensive (5-10 days: 35-70 days graze:rest) short duration grazing system was simulated over a 2-year period after a spring and fall introduction of infestated animals using a model depicting both temporal and spatial processes involved in host-parasite-landscape interactions. The extensive SDG system was infested for 639 and 424 days for spring and fall introductions, respectively. The intensive SDG system was continuously infested throughout the 24-month simulation. Although the intensive SDG system was continuously reinfested, there were more frequent tick-free periods in the fall introduction than the spring introduction. These simulations indicate that rest periods exceeding 150 days are necessary to minimize the rate and extent of spread of ticks in variable rotational grazing systems. These considerations are pertinent to the goals of both control and eradication strategies.