title: A simulation model to investigate interactions between first season grazing calves and Ostertagia ostertagi.
abstract: A dynamic, deterministic model was developed to investigate the consequences of parasitism with Ostertagia ostertagi, the most prevalent and economically important gastrointestinal parasite of cattle in temperate regions. Interactions between host and parasite were considered to predict the level of parasitism and performance of an infected calf. Key model inputs included calf intrinsic growth rate, feed quality and mode and level of infection. The effects of these varied inputs were simulated on a daily basis for key parasitological (worm burden, total egg output and faecal egg count) and performance outputs (feed intake and bodyweight) over a 6 month grazing period. Data from published literature were used to parameterise the model and its sensitivity was tested for uncertain parameters by a Latin hypercube sensitivity design. For the latter each parameter tested was subject to a 20% coefficient of variation. The model parasitological outputs were most sensitive to the immune rate parameters that affected overall worm burdens. The model predicted the expected larger worm burdens along with disproportionately greater body weight losses with increasing daily infection levels. The model was validated against published literature using graphical and statistical comparisons. Its predictions were quantitatively consistent with the parasitological outputs of published experiments in which calves were subjected to different infection levels. The consequences of model weaknesses are discussed and point towards model improvements. Future work should focus on developing a stochastic model to account for calf variation in performance and immune response; this will ultimately be used to test the effectiveness of different parasite control strategies in naturally infected calf populations.
authors: School of Agriculture Food and Rural Development, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. Electronic address: z.berk@newcastle.ac.uk.
authors: Zoe
authors: Z
authors: Berk
authors: The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian, EH25 9RG, Scotland, UK.
authors: Stephen C
authors: SC
authors: Bishop
authors: Scottish Centre for Production Animal Health and Food Safety, School of Veterinary Medicine, University of Glasgow, G61 1QH, Scotland, UK.
authors: Andrew B
authors: AB
authors: Forbes
authors: School of Agriculture Food and Rural Development, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
authors: Ilias
authors: I
authors: Kyriazakis
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000855:Anorexia / Q000469:parasitology / Q000662:veterinary; D002417:Cattle; D002418:Cattle Diseases / Q000276:immunology / Q000469:parasitology*; D003198:Computer Simulation; D004435:Eating; D005243:Feces / Q000469:parasitology; D005260:Female; D005298:Fertility; D006790:Host-Parasite Interactions; D016014:Linear Models; D008297:Male; D008954:Models, Biological; D010028:Ostertagia / Q000276:immunology / Q000502:physiology*; D010029:Ostertagiasis / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D010270:Parasite Egg Count / Q000662:veterinary; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012756:Sheep; D013269:Stochastic Processes; D015431:Weight Loss
keywords: Calves; Gastrointestinal parasites; Immunity; Modelling; Ostertagia ostertagi; Parasite-induced anorexia