title: Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 2. Weather variables associated with development.
abstract: OBJECTIVE
  To identify weather variables associated with the development of eggs of Teladorsagia (=Ostertagia) circumcincta, Trichostrongylus colubriformis and Haemonchus contortus to third-stage infective larvae (L3) under a range of climatic conditions on pasture in the North Island of New Zealand.
  
  
  METHODS
  Sheep faeces containing known numbers of eggs of all three nematode species were deposited on, or buried in, pasture plots at three sites, viz coastal Manawatu, Upper Hutt Valley, and East Cape hill country. Development was measured by recovering L3 from faeces, herbage and soil 28-31 days after deposition, on 13-18 occasions between January 2005 until July 2006. Weather data were recorded at each site, and the association between weather variables and number of L3 recovered was analysed using subsets regression to select best-fitting models from several candidate variables, after adjustment for efficiency of recovery of L3. A multiple linear regression model was then developed for each species, to select weather variables that had both significant and substantive effects on the number of L3 recovered.
  
  
  RESULTS
  For all species, mean daily temperature was the best predictor of the number of L3 recovered (p=0.001). For T.circumcincta the final model included mean daily temperature and soil temperature (R²=51%), and for T. colubriformis the model only included mean daily temperature (R²=55%). For development of H. contortus, mean daily temperature was the most significant variable, but moisture in the form of rainfall entropy, i.e. the temporal distribution of rainfall, over the first 14 days was also significant in the final model (R²=34%).
  
  
  CONCLUSIONS
  Temperature was the most important determinant of developmental success of free-living nematodes on pasture at the study sites, and probably also for other parts of New Zealand with similar climates. Moisture was not significant in the development of T. circumcincta or T.colubriformis, implying that under the generally moist temperate climate in New Zealand, moisture is seldom limiting for development of these species. Haemonchus contortus appeared to be sensitive to moisture availability and precipitation in the first 14 days after deposition of faeces. The results of this study will be further developed as part of species-specific climate-driven models of parasite development in New Zealand.
authors: AgResearch Grasslands, Private Bag 11008, Palmerston North 4442, New Zealand. dean.reynecke@agresearch.co.nz
authors: D P
authors: DP
authors: Reynecke
authors: T S
authors: TS
authors: Waghorn
authors: A-M B
authors: AM
authors: Oliver
authors: C M
authors: CM
authors: Miller
authors: A
authors: A
authors: Vlassoff
authors: D M
authors: DM
authors: Leathwick
mesh_terms: D000818:Animals; D005243:Feces / Q000469:parasitology; D009520:New Zealand / Q000453:epidemiology; D010270:Parasite Egg Count; D012621:Seasons; D012756:Sheep; D012757:Sheep Diseases / Q000453:epidemiology / Q000469:parasitology*; D013997:Time Factors; D014251:Trichostrongyloidea / Q000502:physiology*; D014887:Weather