Investigating the effect of gastrointestinal nematodiasis in Merino sheep on the Northern Tablelands of New South Wales and implications for Integrated Parasite Management

On the Northern Tablelands of NSW, gastrointestinal nematodiasis imposes significant constraints to sheep production. The overall aim of this thesis was to quantify this production loss and evaluate the extent to which it can be ameliorated by integrated parasite management approaches. The general hypothesis tested in this work was that gastrointestinal nematode infection (i.e. worms) present on commercial sheep properties in the Northern Tablelands of NSW induces significant production loss and that worm control utilising Integrated Parasite Management in Sheep (IPM) would reduce this loss and the overall economic impact of worms. ... This research has quantified the biological and economic impact of worms on commercial farms on the Northern Tablelands of NSW in the largest and most comprehensive study of its kind to date. It has shown it to be higher than previous estimates which is primarily due to increased commodity prices. The work has also clearly demonstrated the benefits of Integrated Parasite Management in Sheep in reducing both worm-induced mortality and the overall economic impact of gastrointestinal nematode infection. It is hoped that the information presented in this thesis will ultimately support an increased adoption by industry of sustainable worm control programs

Ecology of the free-living stages of 'Haemonchus contortus' in a cool temperate environment

Current understanding of the ecology of 'Haemonchus contortus' is incomplete and seen as an impediment to effective control of the worm in summer rainfall regions, where outbreaks are common and can result in significant stock mortality. Although there has been a wealth of published research on the effects of temperature on free-living development of 'H. contortus', our level of understanding of how moisture in the micro- and macro-environments influences development to infective larvae on herbage is considerably lower. The current state of knowledge of the free-living ecology of 'H. contortus' is reviewed in Chapter 2, with a particular focus on research findings since the 1970s. Knowledge gaps are highlighted, and a proposal made for a framework on which future investigations of 'H. contortus' can be based in order to improve prediction of free-living development. The key hypotheses under investigation in the experimental studies concerned the quantitative effects of moisture on free-living development of 'H. contortus', and are summarised in Chapter 1 and in further detail in each of the experimental chapters (Chapter 4-6). Plot experiments were conducted in the Northern Tablelands of NSW, where 'H. contortus' is the most important parasite of sheep. Subsequent laboratory experiments, designed in order to extend and explain the findings of the plot experiments, were conducted in programmable incubators in which temperature was regulated to mimic conditions typical to the Northern Tablelands summer. All experiments focused on testing the effects of a range of rainfall and moisture-related variables on 'H. contortus' development from egg through to infective larvae

Moisture requirements for successful development of 'Haemonchus contortus' and 'Trichostrongylus colubriformis' to third stage infective larvae

The overarching aim of the experiments conducted as part of this thesis was to determine the influence of moisture in the form of rainfall events (amount, timing and distribution) and soil moisture (SM) on faecal moisture (FM) and development of 'H. contortus' and 'T. colubriformis' to infective third stage larvae (L3). There are 4 experimental chapters reported in this thesis, (i.e. Chapters 4-7) which were written as a series of publications. ... In order to validate the results of the experiments conducted in controlled climate chambers (Chapters 4-6), a field experiment was conducted to investigate the effects of rainfall timing, rainfall amount and herbage height on translation success with grazing sheep. The results showed that initial SM of 20% alone was sufficient to support development and translation of both GIN species, as there was no effect of rainfall timing, rainfall amount and herbage height on the recovery of GIN species from grazing sheep. These results highlighted the importance of SM as a source of moisture for development of the nematode eggs in the faecal pellets. It also underlined the importance of taking soil moisture into account when predicting the likely effects of rainfall and herbage height on development to L3 and finally in predictive epidemiological models of sheep GIN parasites

Factors influencing Barbervax® immunity and effects on wellbeing and production in Merino ewes and lambs

Barbervax® is a vaccine released in 2014 for use in sheep of all ages to protect them against Haemonchus contortus infection. The overall aims of this thesis were to learn more about the course of action of the vaccine in a commercial environment, simplifying its use on-farm and conducting preliminary observations on performance and production in vaccinated ewes and lambs. The work completed in this thesis is novel, with no previous publication found dealing with the specific hypotheses under test. Chapter 1 consists of a review of the relevant literature including that on the cost of gastrointestinal nematodes to industry, the pathophysiological effects of H. contortus infection in sheep and methods of control. Also reviewed are the development of the immune response to haemonchus infection and the history of development of vaccines against gastrointestinal nematodes, ultimately leading to the production of Barbervax®. Chapter 2 contains the results of an experiment in two phases, each testing a different hypothesis. The first hypothesis was that the duration of vaccinal protection in Merino hogget ewes following a full vaccination course in years 1 and 2 of life would be longer than the claimed 6 weeks. The second hypothesis was that natural exposure to H. contortus infection would boost the Barbervax immune response following a pre-lambing vaccination. A total of 60 age-matched ewes, running together in a larger mob, were split into three treatment groups to test the hypotheses and WEC and ELISA sampled at frequent intervals. Results revealed that neither hypotheses could be supported by the data. In Chapter 3 I tested the hypothesis that the second 'priming' vaccination in lambs could be removed by reducing the marking to weaning interval to 6 weeks and doubling the vaccine dose at marking and/or weaning. The progeny from the group of ewes referred to in Chapter were split into five treatment groups, each with a different vaccine protocol. The results confirmed that the second priming vaccination could be removed with a 6-week marking to weaning interval and provision of a double dose of Barbervax® at either marking or weaning. Finally, in Chapter 4 I report on the effects of the different Barbervax® treatments applied in the previous chapters on ewe and lamb production and performance. Performance measures included; greasy fleece weight, fibre diameter, ewe body condition score and ewe and lamb bodyweights at routine husbandry time points, and transfer of maternal Barbervax® antibody to their progeny prior to weaning. There was clear evidence of maternal transfer of Barbervax® antibody to progeny, but were no negative or positive effects on ewe and lamb performance

Improving the effectiveness of gastrointestinal nematode control for meat-breed lamb production systems on the Northern Tablelands, New South Wales

The experiments reported in this thesis were designed to define and improve the effectiveness of ewe and lamb gastrointestinal nematode control in meat-breed production systems in a summer-dominant rainfall region of NSW Australia. The experiments (Chapters 2-7) reported in this thesis were written as a series of publications. The first step in defining the effect of gastrointestinal nematodes (GIN) on meat-breed lamb production under grazing conditions is the creation and maintenance of uninfected control groups. Experiments conducted under grazing conditions are challenging with difficulties encountered in maintaining uninfected control groups as GIN-free. One method is to serially treat sheep with a combination of short and long-acting anthelmintics to provide effective and continual GIN-suppression

The integration of grazing management and anthelmintic treatment to provide clean lambing paddocks in the northern tablelands region of NSW, Australia

The three experiments described in this thesis have been submitted as research articles to Veterinary Parasitology. Each research article has been included in the thesis as an experimental chapter, essentially as submitted for publication but with the abstract removed

Epidemiological, experimental and diagnostic investigations into an acute paralysis syndrome of broiler chickens in Australia

An acute paralysis syndrome (APS) of broiler chickens was first reported in 2010 in an Australian chicken meat production region. The APS was characterised by flaccid paralysis of the neck, prostration and eventually death of the affected chicken and elevated flock mortalities from 26 days of age. The purpose of the work presented in this doctoral thesis was to establish causation of the APS, risk factors for it and management strategies for controlling it

Application of qRT-PCR for improved understanding and control of infectious bursal disease in chickens

The advent of real time polymerase chain reaction test (qPCR) allows greater diagnostic and research capacity especially beneficial in the field of virology. Infectious bursal disease (IBD) is a well-known viral disease of poultry and occurs world-wide despite widespread use of vaccination. In this thesis study, the real time reverse transcription method (qRT-PCR) was used to address to a range of research questions to provide better understanding and control of IBD in chickens in Australia and world-wide. One experiment was conducted to define the differences between Australian endemic classical and variant infectious bursal disease virus (IBDV) strains by infecting maternal antibody (MAb) free specific pathogen free (SPF) chickens separately with classical strain 06/95 and variant strain 02/95 in isolators. The results revealed that the two IBDV strains did not differ in the degree of bursal atrophy induced, IBDV viral RNA (vRNA) load in bursal and non-bursal lymphoid organs and faecal shedding but variant strain 02/95 induced a greater antibody response to the infection than classical strain 06/95 which was associated with a more rapid decline in IBDV vRNA genome copy number (VCN) in lymphoid organs

Recent research into the Rispens vaccine: Transmission, protection and interaction with wild-type MDV

Internationally there is clear evidence of increased virulence of Marek's disease viruses leading to vaccine failure (Witter 1997, 1998). There is also evidence that vaccination with "imperfect" vaccines (which prevent disease but not infection) has contributed to this (Read et al. 2015). These findings warrant ongoing screening of isolates for virulence and attempts to improve our understanding of interaction between vaccine and wild-type viruses. In Australia we have a good understanding of the level of protection against Marek's disease provided by vaccination with HVT (Meleagrid herpesvirus 1) alone or in combination with MDV serotype 2 (Gallid Herpesvirus 3) vaccine virus (Renz et al. 2012; Walkden-Brown et al. 2013). These studies have also provided good insight into the kinetics and shedding of these viruses in co-infections with serotype 1 wild-type pathogenic MDV (MDV-1, Gallid Herpesvirus 2) (Islam and Walkden- Brown 2007; Islam et al. 2008). Our understanding of these phenomena with regard to the MDV-1 vaccine strain Rispens CVI988 has been held back internationally and in Australia by the apparent good efficacy of the vaccine in the field and the lack of an easy test to differentiate between the Rispens vaccine virus and wild-type MDV1 and provide virus quantification. In 2011 the Australian Egg Corporation Ltd (AECL) funded our research group to develop a qPCR test to differentiate between Rispens and wild-type MDV-1 and to use the test to address a range of issues. This paper summarises our findings over this whole area. Each component has reported separately in detail in journal papers and those papers are cited in this overview

Use of nutritional restriction at mating to dampen reproductive performance of 'FecB'-carrier merino ewes

The nutritional milieu strongly influences ovulation rate in both carriers and non-carriers of the Booroola fecundity gene ('FecB') (Montgomery et al. 1983; Kleemann et al. 1991). On the property 'Allandale' both homozygous ('FecB^BB') and heterozygous ('FecB^B+') merino ewes have large litter sizes (LSs) (2.1 and 2.3 respectively) and excessive losses from ovulation to weaning (>64%) (Walkden-Brown et al. 2007). This study reports an attempt to inhibit the expression of 'FecB' by a period of nutritional restriction, resulting in weight loss at mating