A field trial to control ovine footrot via vaccination and genetic markers

Abstract

Two sheep farms with clinical footrot for several years were selected to compare the efficacy of paucivalent-specific vaccines with a commercially available vaccine (Footvax ®). Furthermore, it was also investigated whether specific DQA 2-haplotypes may cause enhanced footrot-tolerance. Prior to the trial and vaccination of animals, Dichelobacter nodosus-strains isolated from both flocks were used to produce a pentavalent vaccine (containing serogroups A, B, G, H und I) for flock 1 and a quadrivalent vaccine (containing serogroups B, E, G and I) for flock 2. The trial included 695 ewes of German Mutton Merino ( n = 347), German Merino ( n = 115) and German Blackheaded Mutton ( n = 175). During the 16-week trial, the ewes were examined thrice, on weeks 1, 4 and 16. Vaccination was performed during the first and second examination. Prevalence of footrot (evaluated by the number of digits with underrun horn) decreased from 20.2 to 5.9%. Depending on the kind of vaccination, prevalence decreased from 12.3 to 2.5% within the Footvax ®-group, whereas sheep vaccinated with the autogenous vaccine showed a reduction of under-running footrot from 28.4 to 8.9%. Taking into account that vaccination with Footvax ® caused a significantly ( p < 0.001) greater number of local reactions, the autogenous vaccines containing milder adjuvants are recommended for reasons of animal welfare. The DQA 2-locus of 538 ewes was analysed to assess the genetic basis of footrot-tolerance. A total of 21 alleles and 96 genotypes were detected. The most common DQA 2-allele to be found was D ( n = 263), which was also part of the most frequent genotype B1/D ( n = 44). Of all confirmed alleles, 23.4% consisted of a DQA 2-allele accompanied by an additional DQA 2 -like sequence. The likelihood that animals carrying such a duplicated DQA 2-haplotype, had under-running footrot was significantly lower than the odds of ewes lacking the duplication (OR = 1.76 [95% confidence interval: 1.08–2.88], p = 0.02). Comparing single DQA 2-alleles with each other leads to the result that the likelihood of a footrot infection is smaller for ewes having one of the duplicated alleles G and J2 than for ewes carrying the unduplicated alleles E and L (OR L/J2 = 2.09 [95% confidence interval: 1.07–4.10], p = 0.03).