A deterministic model for the demography of the free-living stages of Haemonchus contortus is described. The model consists of three compartments: the pre-infective stages, comprising the eggs and first- and second-stage larvae combined; third-stage larvae in the faeces; and third-stage larvae on the pasture. The mortality (μj) of each of these stages was a function of temperature (K, where K = (degrees Celsius + 30)/100) of the form, μj = aj exp [xj K] + bj exp [– βj K]. The minimum time to second moult (γ) and the moulting rate thereafter (σ) were also functions of temperature (In [1/γ] = c1 + c2[1/K], and σ = d1 exp [d2 K] respectively). The rate at which L3 larvae migrated out of the faeces was treated as a constant (0.165/larva/day).
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