Efficacy of strain-specific footroot vaccines for merino sheep in New Zealand

Authors: Roberston DRH
Publication: Proceedings of the Sheep and Beef Cattle Veterinarians and the Deer Veterinarians Branches of the NZVA, Volume 2022 Proceedings, pp 137-149, Jun 2022
Publisher: Sheep and Beef Cattle Veterinarians Branch of the New Zealand Veterinary Association

Animal type: Sheep
Subject Terms: Vaccination
Article class: Conference Proceedings

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Abstract:

Objective: To evaluate the application customised footrot vaccines (recombinant fimbrial protein or whole cell bacterin – Treidlia Biovet Ltd) administered to merino sheep in New Zealand farming conditions.

Method: The vaccines applied to each farm were based on the specific strain/s (serogroup/s) of footrot bacteria identified on each property tested. Five self-replacing merino properties were selected based on previous foot swabbing information and a general interest in improving tools available to footrot disease control. Four of the farms (A, B, C and D) made available a mob of super-fine merino 2-tooth ewes ranging from 850 to 2,000 animals that had some level of footrot disease present. The trial mobs were vaccinated with either mono or bivalent vaccines appropriate to the strain type(s) identified. The response to a primary and booster vaccination was monitored by comparing pre and post vaccination footrot prevalence. On farm F, a property with multiple strains of footrot, a paired, case-control study with negative control group was undertaken with 200 mixed aged wethers. On this trial mob pre- and post-vaccination footrot prevalence was compared with unvaccinated controls.

Results: In three properties (A, C and D) the footrot prevalence reduced significantly (12% to 4%; 26%to 0.5%; and 50 to 4.8%, respectively). During the trial period on farms A, B, C and D there was no significant spread or new infection, despite environmental conditions that would normally see transmission of the bacteria and disease. Other control measures such as foot bathing was minimal to none. Self-cure effects were apparent but not absolute, with a residual of active footrot infection remaining at low levels in trial mobs. On trial flock B, the footrot prevalence was the same at the start as at the finish of the study period, but at 4% was low to begin with and did not increase despite spending the summer on irrigated pastures. On the multi-strain flock (farm F), the rounds of bivalent vaccine did not have a satisfactory reduction in levels of footrot going form 50% pre- vaccination to 80% post vaccination.

Conclusion: Customised vaccine based on farm strain type of footrot can be an effective tool to control footrot. It could be used as an alternative to, or in conjunction with, traditional footrot control methods. A positive effect is more likely if the is only 1-2 strains of footrot to start with, if the vaccine is compatible with identified strains and no new footrot strains are introduced or discovered on the property. The prolonged protection and increased potency achieved with customised vaccine can improve the production and welfare outcomes of merino sheep in the presence of footrot disease.

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