https://hdl.handle.net/1959.11/56855
Title: | Ecology of Some of the Major Trichostrongylid Parasites of Sheep |
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Contributor(s): | Gyeltshen, Tshering (author); Laurenson, Yan (supervisor); Kahn, Lewis (supervisor) |
Conferred Date: | 2021-05-07 |
Copyright Date: | 2020-11 |
Handle Link: | https://hdl.handle.net/1959.11/56855 |
Related Research Outputs: | https://hdl.handle.net/1959.11/56856 |
Abstract: | Long term sustainable control of gastrointestinal nematode parasites of sheep necessitates the use of a combination of control options. Formulating an appropriate integrated parasite management approach requires a thorough understanding of nematode epidemiology and the ecology of their free-living lifecycle stages. Temperature and water availability have previously been identified as the two most important environmental factors effecting the dynamics of the free-living stages of the nematode lifecycle. Factors directly affecting water availability (e.g. rainfall, soil moisture, relative humidity) exert their impact through the modulation of faecal water content (FWC) which represents the microclimate in which nematode eggs develop to infective larvae. Initial incubation studies investigating the impact of temperature (0, 10, 20, 30 or 40°C) and water addition (1–10 mL) on gravimetric FWC (%) resulted in the formulation of a mathematical model predicting the dynamics of FWC postdeposition (R2 = 0.93). Further validation studies were used to determine whether this model could adequately predict the quantity of water addition required per day to maintain target FWCs of 0, 20, 40, 60 or 80% (R2 = 0.67). Subsequently, faecal samples containing monospecific infections of Trichostrongylus vitrinus, Trichostrongylus colubriformis and Teladorsagia circumcincta were incubated at constant target temperatures (0, 10, 20, 30 and 40°C) and target FWCs (0, 20, 40, 60 and 80%) for 8 days. Temperature and FWC had a significant effect (p<0.05) on the daily counts of eggs, pre-infective larvae, intra-pellet infective larvae and extra-pellet infective larvae. Development of eggs to intra-pellet infective larvae were observed at target temperatures of 20 and 30°C for all species with few T. colubriformis also developing at 40°C. To elucidate the survival and development/migration rates of each lifecycle stage, the experimental data was used to parameterise the mathematical model of Laurenson and Kahn (2018) for T. vitrinus (R2 = 0.70), T. colubriformis (R2 = 0.68) and T. circumcincta (R2 = 0.73). The predicted optimum temperature (and FWC, %) for the development and migration of T. vitrinus, T. colubriformis and T. circumcincta eggs to extra-pellet infective larvae were 23°C (73%), 25°C (60%), and 24°C (71%), respectively. The results from this study highlight the importance of temperature and FWC for the development of eggs to infective larvae and conform to the predominance of T. vitrinus and T. colubriformis in cooler and moist climatic conditions and T. colubriformis in warmer and drier regions. |
Publication Type: | Thesis Doctoral |
Fields of Research (FoR) 2008: | 070704 Veterinary Epidemiology 070708 Veterinary Parasitology 079999 Agricultural and Veterinary Sciences not elsewhere classified |
Fields of Research (FoR) 2020: | 300905 Veterinary epidemiology 300909 Veterinary parasitology |
Socio-Economic Objective (SEO) 2008: | 830310 Sheep - Meat 830311 Sheep - Wool 860902 Veterinary Diagnostics |
Socio-Economic Objective (SEO) 2020: | 100412 Sheep for meat 100413 Sheep for wool 241602 Veterinary diagnostics |
HERDC Category Description: | T2 Thesis - Doctorate by Research |
Description: | Please contact rune@une.edu.au if you require access to this thesis for the purpose of research or study. |
Appears in Collections: | School of Environmental and Rural Science Thesis Doctoral |
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