title: Development of a simulation model to evaluate the effect of vaccination against Tritrichomonas foetus on reproductive efficiency in beef herds.
abstract: OBJECTIVE
  To develop a model to evaluate the effect of vaccination against Tritrichomonas foetus on reproductive efficiency in beef herds.
  
  
  METHODS
  A beef herd of 300 cows and 12 bulls (8 bulls < or = 3 years old and 4 bulls > 3 years old).
  
  
  METHODS
  The model was developed by use of data for various risk factors and vaccine efficacy. The reference herd was considered to be one in which T. foetus had been diagnosed and bulls were tested for T. foetus before the breeding season. Five thousand iterations were run for each of 13 simulations, with each simulation representing a separate combination of risk factors.
  
  
  RESULTS
  In all simulations, vaccination resulted in significantly higher calving incidence than nonvaccination. Shared grazing was found to be the most significant risk factor for a decrease in calving incidence attributable to T. foetus infection, followed in importance by lack of testing before the breeding season and a higher proportion of old bulls. Combinations of risk factors contributed to a loss of income of up to 22%, some of which could be blunted by vaccination.
  
  
  CONCLUSIONS
  Highest calving incidence is achieved when all bulls are tested for T. foetus before the breeding season and all bulls with positive culture results are culled. Avoiding all risk factors is better than vaccinating, but when this is not feasible for a given herd, the results of this simulation indicate that proper vaccination can decrease economic losses attributable to abortions caused by T. foetus.
authors.affiliation: Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
authors.forename: Aurora
authors.initials: A
authors.lastname: Villarroel
authors.forename: Tim E
authors.initials: TE
authors.lastname: Carpenter
authors.forename: Robert H
authors.initials: RH
authors.lastname: BonDurant
mesh_terms: D000383:Agriculture / Q000191:economics; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000191:economics / Q000469:parasitology* / Q000503:physiopathology; D003198:Computer Simulation; D008954:Models, Biological; D011528:Protozoan Infections / Q000503:physiopathology; D011529:Protozoan Infections, Animal; D012098:Reproduction; D012307:Risk Factors; D016835:Tritrichomonas foetus; D014611:Vaccination / Q000662:veterinary*