title: No loss of production due to larval challenge in sheep given continuous anthelmintic treatment via a controlled release capsule.
abstract: This study aimed to quantify production loss due to larval challenge in sheep administered a controlled release albendazole capsule (CRC) and thus determine the suitability of CRC treated sheep as a proxy for worm-free sheep in grazing experiments. The experiment used an incomplete 2 × 3 latin square design with 81 Merino wethers. Sheep were either infected (INF) with mixed oral infection of albendazole-susceptible Haemonchus contortus, Trichostrongylus colubriformis, and Teladorsagia circumcincta (initial bolus then thrice weekly maintenance) or remained uninfected (UINF). Worm control treatments were with a CRC (CRCT), threshold treatment with a short-acting anthelmintic when worm egg count (WEC) exceeded 1500 epg (TT) or untreated (UT). The experiment was conducted in two 63-day periods (separated by a 14 day washout period) with infection treatments swapped between periods. A subset of animals was killed at the end of each period for worm counts and tissue sampling. Faecal worm egg count in UINF-UT reached 10,204 and 6078 epg at day 63 in periods 1 and 2, respectively, and remained 0 throughout in the CRT treatments. There was no difference in live weight gain or wool growth of INF-CRCT sheep (67 and 70 g/d) relative to UINF-CRCT (67 and 76 g/d). Live weight gain was significantly lower in INF-UT (27 g/d) and INF-TT (55 g/d) than UINF-UT (88 g/d) or UINF-TT (81 g/d) treatments. During the first infection period, greasy fleece weight growth was significantly lower in INF-UT (6.33 g/d) and INF-TT (6.37 g/d) than UINF-UT (7.80 g/d) or UINF-TT (7.32 g/d) treatments. The effects of infection on production persisted in INF-UT, but not INF-TT sheep for several weeks after termination of infection. Eosinophil counts were elevated in all infected groups and the antibody response to T. colubriformis was greater in INF-CRCT and INF-TT groups compared to uninfected sheep. Together, these results indicate that larval challenge in sheep with a CRC is mildly immunogenic but is not associated with production loss. The results also showed that the CRC itself reduced live weight gain and that anthelmintic treatment at a WEC threshold of 1500 epg reduces production loss during infections and prevents persistence of adverse effects following infection.
authors.affiliation: CRC for Sheep Industry Innovation and School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia. gkelly4@une.edu.au
authors.forename: G A
authors.initials: GA
authors.lastname: Kelly
authors.forename: S W
authors.initials: SW
authors.lastname: Walkden-Brown
authors.forename: L P
authors.initials: LP
authors.lastname: Kahn
mesh_terms: D015766:Albendazole / Q000008:administration & dosage* / Q000627:therapeutic use; D000818:Animals; D000909:Antibodies, Helminth / Q000276:immunology; D000969:Antinematodal Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D060085:Coinfection / Q000188:drug therapy / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D003692:Delayed-Action Preparations / Q000008:administration & dosage / Q000627:therapeutic use; D005243:Feces / Q000469:parasitology; D005260:Female; D006188:Haemonchiasis / Q000188:drug therapy / Q000276:immunology / Q000469:parasitology / Q000662:veterinary; D006189:Haemonchus / Q000187:drug effects / Q000502:physiology; D007814:Larva / Q000187:drug effects; D008297:Male; D009517:New South Wales; D010270:Parasite Egg Count / Q000662:veterinary; D011156:Population Density; D011897:Random Allocation; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy / Q000276:immunology / Q000469:parasitology*; D013997:Time Factors; D014251:Trichostrongyloidea / Q000187:drug effects* / Q000502:physiology; D014252:Trichostrongyloidiasis / Q000188:drug therapy / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D014253:Trichostrongylosis / Q000188:drug therapy / Q000276:immunology / Q000469:parasitology / Q000662:veterinary; D014254:Trichostrongylus / Q000187:drug effects / Q000502:physiology; D015430:Weight Gain; D014935:Wool / Q000254:growth & development
chemical_list: D000909:Antibodies, Helminth; D000969:Antinematodal Agents; D003692:Delayed-Action Preparations; D015766:Albendazole