Melbourne Veterinary School - Theses
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ItemAssessing and addressing the welfare of extensively managed ewes( 2019)The sheep industry is currently facing increasing social demands for assurances of good animal welfare, which indicates that assessing and addressing the welfare of sheep is critical if the current ‘social license to farm sheep’ is to be maintained. Farmers are key players in improving sheep welfare because they are responsible for the care of their animals and make the management decisions on their farm. Hence, a better understanding of the main factors underpinning farmer behaviour is important. According to the Theory of Planned Behaviour, farmer attitudes towards sheep management are likely to influence their behaviour in terms of the implementation of improved management practices. Subsequently, farmer management behaviour may impact on the welfare of their sheep. The aim of this thesis was therefore to examine the relationships between farmer attitudes, management behaviour and sheep welfare outcomes. To examine these relationships, animal welfare assessments and questionnaire interviews with farmers were conducted. A total of 6200 ewes (aged 2-5 years) and 32 farmers were sampled across Victoria, Australia. Farms were visited at mid-pregnancy and weaning, and the ewes were examined using six animal-based measures: body condition score (BCS), fleece condition, skin lesions, tail length, dag score and lameness. In addition, the number of ewes that needed further inspection/care (such as sick or injured sheep) was recorded and reported to the farmers. The welfare of the ewe flocks, based on the six indicators measured, was good overall. However, individual welfare compromise was considered significant. There were 185 (3.0%) ewes needing further care and cases were identified in all farms. Main reasons for further inspection/care were lameness or foot-related issues, BCS ≤ 2 and active dermatophilosis or broken wool. Farmer attitudes to sheep and management were in general positive and welfare was considered an important aspect of farm productivity. In terms of management, it was found that farmers relied mostly on visual monitoring to assess the flocks and pasture quality and quantity. However, close inspection of the flock and more detailed practices such as body condition scoring of sheep, veterinary interventions or keeping accurate records were less common activities. Indeed, mortality rates were frequently underestimated. Positive farmer attitudes were associated with positive management behaviour (active management style), and positive management behaviour was associated with positive ewe welfare outcomes. Farmers with an active management style had fewer ewes in need of further inspection/care after both welfare assessments (mid-pregnancy and weaning). Main results indicated that farmers were more likely to perform an activity (management behaviour) if they perceived the activity was valuable (behavioural attitudes) and if they perceived the activity could be realised (perceived behavioural control). The results of this thesis demonstrate that there is an opportunity to create change in farmer management behaviour and potentially improve sheep welfare via education programs targeting attitudinal change. The results reported in this thesis provide what is believed to be the first comprehensive study investigating the on-farm welfare of extensively managed ewes and the farmer-sheep relationship in extensive systems. Controlled trials to assess if education programs or other interventions are able to improve farmer attitudes and management behaviour, as well as sheep welfare, would allow causality to be investigated and would be a valuable next research step following on from the current work.
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ItemImproving disease surveillance in Australia’s sheep industries: investigations of syndromic surveillance, farmer behaviour and sheep trade networks( 2018)Designing and delivering effective, useful livestock health surveillance is a challenge for many countries. The observations of people in frequent contact with livestock, captured through passive surveillance, play an important role in many national surveillance systems. In Australia, the effectiveness of passive surveillance on sheep and beef farms has been limited by infrequent veterinary contact. Farm workers frequently observe signs of disease in livestock, but these observations are not captured by existing surveillance systems. This thesis therefore posed the question: can farmers’ observations be collected to generate useful surveillance information? Syndromic surveillance of farmers’ observations is one approach to increase data capture from extensive livestock farms. Chapter 3 describes the operation of a syndromic surveillance system collecting farmers’ observations of livestock health in Victoria, Australia, over its first two years of operation from 2014 to 2016. Survival analysis and classification and regression tree analysis were used to identify farm level factors associated with reliable participation, to inform future recruitment aimed at farmers who were willing and able to provide regular, timely reports. Farmers keeping only sheep were the most reliable and timely respondents, while farmers aged under 43 years or working full time on-farm had lower response rates than older farmers or part-time farmers. This chapter demonstrates that recording farmers’ observations of signs of disease using syndromes is a feasible and effective method to gather disease occurrence data. The utility of syndromic data is further investigated in Chapter 4, using the observations collected by the surveillance system to quantify ewe mortality on sheep farms in southern Australia. Ewe deaths were reported in 540 of 612 reports, describing 2106 individual deaths, with a median of 4 deaths per positive monthly report. Median mortality rates ranged between individual farms from 1 to 5 deaths/1000 ewes/month. The incidence rate ratio of mortality in the five months preceding and following lambing was 2.8 (95% CI 2.0 to 4.1) compared to the remaining seven months of the year. Overall ewe mortality could therefore be reduced through strategies targeted to improving peri-parturient ewe survival. In a subset of reports where veterinary contact was recorded, just 15% of reported deaths involved a veterinarian. Further investigation of how and why farmers respond to ewe deaths without veterinary support is needed, to determine the best farm management strategies to reduce mortality. Chapter 5 investigates Australian sheep farmers’ low rates of veterinary contact. The study aimed to understand why Australian sheep farmers chose not to contact veterinarians when their animals showed signs of disease, and what alternative approaches they took to managing unwell animals. Data were collected during three focus group discussions with sheep farmers in Victoria, Australia. Transcripts of those discussions were analysed using a modified grounded theory approach to develop a preliminary theory of Australian sheep farmers’ disease response behaviour. Critical steps in the decision-making process included the farmer recognising that action is needed, and then deciding what that action would be. The farmers reported having to decide whether they would act independently based on their previously experiences, or alternatively to seek advice. Veterinarians played a small but important role as potential advisors, alongside others including trusted farming friends and farmer discussion groups. Self-reliance and confidence in their knowledge and skills was highlighted as the main reason the farmers often chose not to seek veterinary advice. Rather than being seen as a barrier to effective passive surveillance, the actions that arise from farmers’ self-reliance when facing disease should be taken into account when designing novel surveillance approaches. A final consideration for observational disease surveillance is the selection of individuals to contribute data to the system. While characteristics associated with participation may guide recruitment as described in Chapter 3, it is also useful to target surveillance to farms that have increased risk of acquiring or disseminating disease. The movement of animals between farms contributes to infectious disease spread, and can be investigated through network analysis methods. Australia’s National Livestock Identification Scheme sheep movement records are suitable for such analyses, but are known to be a targeted subset of all sheep movement in the country. However, knowledge of the effect of sampling or incomplete network data on these studies is limited. In Chapter 6, a simulation algorithm is presented that provides an estimate of required sampling proportions based on predicted network size, density and degree value distribution. The algorithm may be applied a priori to ensure network analyses based on sampled or incomplete data provide population estimates of known precision. Results demonstrate that, for network degree metrics, sample size requirements vary with sampling method. Where simulated networks can be constructed to closely mimic the true network in a target population, this algorithm provides a straightforward approach to determining sample size under a given sampling procedure for a network metric of interest. Chapter 7 then presents analysis of National Livestock Identification Scheme sheep movement data for Victoria, Australia. The sheep movement network in Victoria shows typical livestock movement network characteristics including scale-free and small-world topology, small diameter and short average path lengths, supporting the assumption that disease could spread rapidly in the state through sheep movements if it were not detected rapidly. Victoria’s position as a net importer of sheep and sheep flow is confirmed, driven substantially by the activity of saleyards (livestock markets) and abattoirs. Little variation within or between years in overall movement patterns were detected. While most farms are connected to a very small number of properties in the network, small subsets of farms demonstrate high degree values (being directly connected to many other properties through incoming out outgoing animal movements) or high frequency of sheep purchases or sales. These farms may be useful targets for emerging surveillance methods that can be implemented on-farm. Together, these studies provide new information about the Australian sheep industry and the feasibility of new surveillance approaches to improve the effectiveness of surveillance. By describing farmer behaviour, livestock movements patterns and the feasibility of syndromic surveillance approaches to capture farmers’ observations of signs of disease, these studies justify further development and implementation of novel surveillance approaches in Australia and serve as an example for other countries facing similar surveillance challenges. While there is no ideal surveillance system, integrating new approaches into wider surveillance strategies can improve the quality of information generated by surveillance, to better describe true disease states in the population and drive appropriate response activities.
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ItemThe effect of vaccination against Campylobacter on maiden ewe reproduction in Victoria( 2017)Reducing reproductive wastage is important for the Australian sheep industry. Campylobacter fetus fetus and C. jejuni infections in ewes contribute to reproductive wastage through abortions, stillbirths and the birth of small, weak neonates, potentially at greater risk of starvation-mismothering-exposure (SME). A combined vaccine against C. fetus fetus and C. jejuni (Ovilis Campyvax®, MSD Animal Health) is registered in Australia to reduce reproductive wastage due to Campylobacter, but few independent field trials of the vaccine have been conducted in commercial flocks. This study described the effects of Ovilis Campyvax® on maiden ewe reproduction in a randomised controlled field trial on four winter-/spring-lambing Victorian sheep farms. Conception and lamb marking rates were compared amongst nineteen-month-old Merino and Merino-cross ewes randomly allocated to vaccination or control groups at mating on each farm (each n = 211–249/group). Ewes were grazed together from mating until immediately before lambing, when they were set-stocked in treatment groups in matched paddocks. Antibody titres to Campylobacter spp. were measured at mating, mid-gestation pregnancy diagnosis and lamb marking in a subset of ewes. A cross-sectional study of cause of neonatal lamb mortality was also conducted on each farm during lambing. Vaccination had no effect on ewe conception rate (67% to 117% depending on farm). Two of four farms had serological evidence of prior exposure to C. fetus fetus, and variable exposure to this organism occurred during gestation on all farms. Campylobacter jejuni titres were high on all farms at mating, but decreased thereafter. Despite serological evidence of a good response to C. fetus fetus vaccination on all farms, vaccination did not significantly increase lamb marking rates (63% to 100%, depending on farm). The main causes of lamb mortality were dystocia, starvation-mismothering-exposure and predation. There was a suggestion of a difference in the pattern of causes of neonatal lamb mortality between vaccinated and control ewes. The difference was not statistically significant, but corresponded with anecdotal observations made by the flock owners. Additional large scale studies into vaccination and the causes of neonatal lamb mortality are needed to further investigate these observations. Vaccination appeared to prevent Campylobacter-associated neonatal lamb mortality and morbidity on the farm with the greatest exposure to C. fetus fetus. On that farm, 55% of unvaccinated ewes that failed to rear a lamb had ‘high’ (≥ 1:80) C. fetus fetus titres, compared to 0% of ewes that successfully reared a lamb. Additionally, C. fetus fetus was only recovered from necropsied lambs born to unvaccinated ewes. The results demonstrate that ewes can be vaccinated with Ovilis Campyvax® during mating without impacting conception rates. However, the effect of Campylobacter vaccination on reproductive output is complex and multifactorial. Vaccination effects may be obscured by other causes of reproductive loss. Vaccination may reduce the contribution of Campylobacter infections to lamb loss due to SME. However, the dystocia risk in protected ewes may increase depending on ewe nutrition. If this is the case, the nutrition of vaccinated ewes could be managed more economically to obtain the full benefits of vaccination. This is an avenue for future research.