Veterinary Science Collected Works - Theses
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ItemSouth-west Victorian dairy herd gastrointestinal parasite prevalence study( 2022)It is widely accepted that healthy adult cattle are generally not affected by worm burdens. However, the stress of intensive dairy situations globally has been thought to reduce cows’ immunity to gastrointestinal parasites and subsequently allow milk production losses due to these parasite burdens. Numerous global studies have indicated production benefits to anthelmintic use in lactating dairy cattle, but there have also been several publications showing marginal or no significant milk production benefit following anthelmintic use. Anthelmintic resistance has been illustrated in multiple studies and is likely to be reducing the overall production benefit seen with anthelmintic use. In adult cattle our gastrointestinal parasite measurement systems are largely flawed or insensitive. The aim of this project was to assess the use of highly sensitive faecal egg counts (FEC) to document the gastrointestinal worm burden of lactating dairy cows in south-west Victoria. We also aimed to investigate the relationship between farm management, previous anthelmintic use, milk production, faecal egg count and bulk milk anti-O. ostertagi antibody ELISA optical density ratio (ODR) testing in this region. Sensitive FECs from individual recently calved adult dairy cows were obtained through use of a modified Mini-FLOTAC procedure achieving an analytical sensitivity of 2.5 eggs per gram of faeces (epg). Individual faecal egg counts were collected on 18 farms from cohorts of primiparous and multiparous recently calved cows. Vat milk was also collected on the day of faecal sampling for laboratory assessment of ODR. Milk production data was available from 10/18 farms providing 247 individual milk production records. Faecal egg counts greater than or equal to 2.5 epg were much more likely to be recorded in primiparous cows (45%) than in multiparous cows (26%). Multiparous cows with a body condition score of < 4 were significantly more likely to have a positive FEC when compared with higher conditioned multiparous cows (p=0.002). O. ostertagi was the most abundant gastrointestinal species amongst all cohorts on all farms making up 85% of overall larvae cultured. ODR was not related to mean FEC on corresponding farms, nor was it related to the proportion of individual animals with a FEC greater than or equal to 2.5, 5 or 10 epg. ODR was strongly related to the interval, in days, between calving and prior anthelmintic use. Milk production data was analysed for the first 100 days of lactation and was divided into two groups: primiparous and multiparous. The primiparous cohort had a much higher proportion of animals with FEC greater than or equal to 2.5epg and produced on average 29% less milk than the multiparous cohort, subsequently the primiparous and multiparous groups were analysed separately. Across both primiparous and multiparous data sets, we did not observe a difference in the milk production of FEC positive or negative cows at various cut point thresholds (2.5, 5 or 10 epg. Great variation across farms was seen with milk production, when data was arranged into quartiles, based on production relative to peers on each farm, we did not observe a relationship between FEC and milk production. Mini-FLOTAC and sensitive FECs are successful in identifying adult cattle with worm burdens, but the application of these tests requires further investigation to make treatment or management guidelines. ODR should not be used as a sole decision-making tool in assessment of the requirement for anthelmintic use in pasture based dairy cattle of south-west Victoria. We did not find a difference in milk production of cows with and without FECs at 2.5 or 10 epg, because of these findings we would not suggest that FEC is useful in differentiating animals that may or may not benefit from anthelmintic treatment. Further work is required to establish a means to select individual cows for beneficial anthelmintic treatment.
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ItemStudies on gastrointestinal nematodes of alpacas in Australia( 2019)The Australian alpaca industry has grown remarkably since the re-introduced of alpaca into the country in the 1980s. This relatively new and small industry faces various challenges that affect the overall production (fibre, meat etc.) of animals. For example, production losses and deaths associated with gastrointestinal nematodes (GINs) have become one of the major concerns for alpaca producers in Australia and elsewhere as there is a scarcity of reliable information about the epidemiology of GINs in alpacas, worm control practices used by alpaca farmers and the efficacy status of widely used unregistered anthelmintics. The present thesis aimed to (i) assess worm control practices used by Australian alpaca farmers, (ii) determine the epidemiology GINs and (iii) the efficacy of commonly used anthelmintics against GINs of alpacas in Australia. A comprehensive literature review along with seven results chapters and a general discussion chapter are included in this thesis. In Chapter 2, an online questionnaire survey was conducted to assess worm control practices used by Australian alpaca farmers. Results showed that more than half of the respondents perceived that GINs was an important health problem. Macrocyclic lactones (MLs) were the most commonly used anthelmintics in alpacas. Almost half of the respondents (47%) used anthelmintics at the dose rate recommended for sheep. The majority of alpaca farmers were unaware of pasture spelling and one-third of respondents had shared paddocks with ruminants. This study led to subsequent studies to understand the epidemiology of GINs of Australian alpacas using sensitive diagnostic methods and assess the efficacy of commonly used anthelmintics against GINs of Australian alpacas. In chapters 3 and 4, sensitive diagnostic methods were developed to determine the faecal eggs counts and identify nematode genus/species in the faeces of alpacas. In chapter 3, a newly developed diagnostic method, the FECPAKG2, was compared to a routinely used method, the McMaster technique, for the counting of GIN eggs in the faeces of alpacas. Data revealed moderate to good agreement between the two methods. This was the first study to assess the agreement of measurements between two methods for estimating nematode eggs in the faeces of alpacas. In Chapter 4, a molecular diagnostic tool based on multiplexed-tandem PCR (MT-PCR) was developed. This tool is faster and is capable of identifying common nematode genera/species of alpacas, including Camelostrongylus mentulatus which was not possible using traditional larval culture method. The epidemiology of GINs of alpacas in Australia was assessed using cross-sectional (Chapter 5) and longitudinal studies (Chapter 6). A range of GINs are prevalent in Australian alpacas with variable worm burdens in different climatic zones and seasons. The results of both studies were comparable. Both studies showed an overall prevalence of GINs in SACs from 61 – 66%. Weaners had the highest prevalence in both studies ranging from 73 - 80%. However, the pattern of prevalence was not same across the climatic zones. In cross-sectional study, the highest prevalence of GINs (77%) were observed in the summer rainfall zone, whereas in longitudinal study the winter rainfall zone had the highest prevalence (68%). In addition, a mixed-effects zero-inflated negative binomial (ZINB) regression model has been used to design parasite control interventions. To assess worm burden and the spectrum of GINs infecting Australian alpacas, 100 gastrointestinal tracts of alpacas were examined (Chapter 7). Results revealed a mean burden of 1,300 worms, with the highest burden of 29,000 worms. Nineteen different species of GINs were identified from Australian alpacas, including three camelid specific nematodes: Graphinema auchenia, Camelostrongylus mentulatus and Trichuris tenuis. Haemonchus contortus was the most prevalent nematode followed by C. mentulatus and Trichostrongylus spp. In Chapter 8, the efficacy of commonly used anthelmintics against GINs of alpacas was assessed. The faecal egg count reduction tests were conducted on 20 alpaca farms across the country. The results showed that a commercially available combination of levamisole, closantel, albendazole and abamectin was the most effective dewormer followed by single anthelmintic such as, monepantel, moxidectin, closantel, fenbendazole and ivermectin. Haemonchus spp. were the most commonly resistant nematodes. This was the first comprehensive study to investigate the efficacy of commonly used anthelmintics against GINs of alpacas. This study provides significant information on GINs of Australian alpacas. Results of this study advance our knowledge on the epidemiology and control of GINs and efficacy status of most commonly used anthelmintics which could be used to develop control strategies against GINs of alpacas in Australia.