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

Abstract

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.<br/> 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®.<br/> 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.<br/> 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.<br/> 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.