title: Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 1. Patterns of seasonal development.
abstract: OBJECTIVE
  To describe the seasonal pattern of development of third-stage infective larvae (L3) from eggs of Teladorsagia (=Ostertagia) circumcincta, Trichostrongylus colubriformis and Haemonchus contortus 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 and July 2006. Analysis of the number of larvae recovered used a mixed model including number of eggs deposited, weight of faeces recovered (an assumed indicator of earthworm activity), site, contamination date, and position of deposited faeces, i.e. on the surface or buried.
  
  
  RESULTS
  There was a significant effect of contamination date on development of all three species, with maximum numbers of L3 developing between late spring (November) and early autumn (March), and minimum numbers in June and July. There were large differences between species, with H. contortus exhibiting a long period (April to October) where development was close to zero, whereas T. circumcincta developed to some extent all year round. Development of T. colubriformis was intermediate between the other two species. Burying faeces containing nematode eggs increased the number of L3 recovered compared with surface deposition (p ≤ 0.001), although there were a small number of exceptions involving only T. colubriformis. The weight of faeces recovered at harvest, which was assumed to be an indication of earthworm activity, was correlated with the number of L3 recovered for all species (p<0.001). In a separate analysis, earthworms were assumed to have been active if <5 g faeces remained at harvest. Where this occurred, the number of L3 of T. colubriformis and T.circumcincta recovered was reduced by 56% and 58%, respectively (p<0.001).
  
  
  CONCLUSIONS
  A marked seasonal pattern of development was observed for all three species, with the most larvae developing in spring-early autumn and the least in winter. This seasonal pattern was most pronounced in H. contortus and least obvious in T. circumcincta. Burying faeces containing eggs generally resulted in more L3 being recovered, whilst the apparent activity of earthworms resulted in fewer larvae being recovered.
authors: AgResearch Grasslands, Private Bag 11008, Palmerston North 4442, New Zealand.
authors: T S
authors: TS
authors: Waghorn
authors: D P
authors: DP
authors: Reynecke
authors: A-M B
authors: AM
authors: Oliver
authors: C M
authors: CM
authors: Miller
authors: A
authors: A
authors: Vlassoff
authors: J P
authors: JP
authors: Koolaard
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*