title: Risk factors for Merino ewe mortality on the Northern Tablelands of New South Wales, Australia.
abstract: OBJECTIVE
  To measure the association of worm egg count (WEC), body weight (BW) and fat score (FS) with mortality in Merino ewes.
  
  
  METHODS
  On six farms, Merino ewes (n = 1440) were yarded at approximately 3-month intervals for 2 years for a range of experimental measurements. Mortality was defined by failure to present at two consecutive measurement days and at next shearing. Survival analysis was conducted with phenotypic traits measured both as continuous variables and categorised appropriately for industry guidelines.
  
  
  RESULTS
  Overall mortality was 10%, with most deaths occurring in autumn followed by winter. Age class (2006 drop vs mature-age ewes) did not affect mortality. High WEC, low BW and low FS significantly increased the risk of mortality. WEC > 1200 epg significantly increased risk of mortality in summer (risk ratio 3.76) and autumn (risk ratio 3.61) compared with the reference group. Risk of mortality increased 1.1-fold for each kilogram unit decrease in BW and 7-fold for each unit decrease in FS.
  
  
  CONCLUSIONS
  Mortality of Merino ewes can be significantly reduced by management methods that reduce WEC, maintain BW and increase the FS. For Merino ewes on the Northern Tablelands of NSW, improved animal welfare and economic benefits may be achieved by maintaining sheep with WEC < 1200 epg, BW > 35 kg and FS > 2.5.
authors.affiliation: Cooperative Research Centre for Sheep Industry Innovation and School of Environmental and Rural Science, University of New England, Armidale, New South Wales, Australia.
authors.forename: G A
authors.initials: GA
authors.lastname: Kelly
authors.forename: L P
authors.initials: LP
authors.lastname: Kahn
authors.forename: S W
authors.initials: SW
authors.lastname: Walkden-Brown
mesh_terms: D000273:Adipose Tissue; D000822:Animal Husbandry / Q000379:methods / Q000706:statistics & numerical data; D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage; D001835:Body Weight; D005260:Female; D006374:Helminthiasis, Animal / Q000401:mortality / Q000517:prevention & control; D009517:New South Wales / Q000453:epidemiology; D010270:Parasite Egg Count / Q000662:veterinary; D011897:Random Allocation; D012307:Risk Factors; D012621:Seasons; D012756:Sheep; D012757:Sheep Diseases / Q000209:etiology* / Q000401:mortality* / Q000469:parasitology / Q000517:prevention & control; D016019:Survival Analysis
chemical_list: D000871:Anthelmintics
keywords: Merinos; Northern Tablelands; gastrointestinal nematodes; growth rates; mortality; survival analysis