title: Assessment of the effect of gastrointestinal nematode infestation on weight gain in grazing beef cattle.
abstract: OBJECTIVE
  To assess the effect of subclinical, naturally acquired gastrointestinal nematode infestation on weight gain in yearling cattle kept on pasture.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  799 Bos taurus yearlings kept on pasture with 2,805 herd mates in eastern and central South Dakota.
  
  
  METHODS
  11 trials were initiated at 9 sites from 1999 through 2001. For each trial, approximately 10% of cattle in each site's pasture group were identified, weighed, and administered a bolus of ivermectin (sustained-release formulation) prior to turnout. A similar subgroup of nontreated control cattle was identified and weighed prior to turnout. For each trial, treated and control groups remained with the larger pasture group throughout the entire grazing season. At the end of the grazing season, weight measurements and fecal samples were obtained from all treated and control cattle; average daily grazing gain was calculated and compared between these 2 groups.
  
  
  RESULTS
  Treatment of grazing cattle with ivermectin increased average daily gain by 0.0459 +/- 0.01 kg/head/d (mean +/- SEM; 0.1 +/- 0.02 lb/head/d), compared with that achieved in control cattle. Control cattle had significantly greater fecal egg counts at grazing season end than treated cattle.
  
  
  CONCLUSIONS
  Compared with anthelmintic-treated cattle, yearling cattle with naturally occurring gastrointestinal nematode infestations kept on pasture in the US Northern Plains had a decreased average daily gain equivalent to 6.6 kg (14.5 lb) less gain in a 143-day grazing season. Strategies for control of nematode populations in pastures should be considered to ameliorate this production loss.
authors.affiliation: Department of Biology and Microbiology, College of Agriculture and Biological Sciences, South Dakota State University, Brookings, SD 57007, USA.
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Mertz
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hildreth
authors.forename: William B
authors.initials: WB
authors.lastname: Epperson
mesh_terms: D000818:Animals; D000969:Antinematodal Agents / Q000627:therapeutic use*; D002417:Cattle / Q000254:growth & development*; D002418:Cattle Diseases; D005243:Feces / Q000469:parasitology; D007411:Intestinal Diseases, Parasitic / Q000150:complications / Q000188:drug therapy / Q000662:veterinary*; D007559:Ivermectin / Q000627:therapeutic use*; D009349:Nematode Infections / Q000150:complications / Q000188:drug therapy / Q000662:veterinary*; D010270:Parasite Egg Count / Q000662:veterinary; D011446:Prospective Studies; D013023:South Dakota / Q000453:epidemiology; D016896:Treatment Outcome; D015430:Weight Gain
chemical_list: D000969:Antinematodal Agents; D007559:Ivermectin