Melbourne Veterinary School - Theses
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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.