Felduntersuchung zur Bekämpfung der Moderhinke bei Schafen mittels Vakzinen und genetischer Marker

Two sheep farms having problems with footrot infections for several years were elected to compare the efficacy of paucivalent specific vaccines with the commercial polyvalent vaccine (Footvax®, ESSEX Tierarznei, Munich). Furthermore it was investigated whether certain DQA2-haplotypes cause enhanced footrot-tolerance. 807 ewes belonging to the breeds German Mutton Merino (n = 439), German Merino (n = 142) and German Blackheaded Mutton (n = 226) were examined. Prior to the actual trial, Dichelobacter nodosus-strains were isolated from both flocks. These strains were used to produce a pentavalent vaccine (containing serogroups A, B, G, H und I) to be used in flock 1 and a quadrivalent vaccine (serogroups B, E, G and I) for the use in flock 2. During the 16-week trial the ewes were inspected three times (in week 1, 4 and 16). The vaccination was applied in the course of the first and the second investigation. Altogether the prevalence of footrot - measured by the number of claws with underrun horn - decreased from 20,20 % to 5,90 %. Depending on the kind of vaccination, the footrot-prevalence decreased from 12,3 % to 2,5 % within the polyvalent, commercial vaccinated group, whereas the autogenous vaccinated sheep showed an improvement from 28,4 % to 8,9 %. Due to the design of the trial neither of the vaccines can be qualified superior in regarding the prophylactic and therapeutic effect. Conditional on the fact that the application of Footvax® which contains mineral oil as an adjuvant, caused a significant (p = < 0,0001) greater number of reactions at the injection site, autogenous vaccines containing milder adjuvants (e.g. aluminium hydroxide) are to be preferred for reasons of animal welfare. The DQA2-locus of 538 ewes was analysed to assess genetic footrot-tolerance. A total of 21 allels and 96 genotypes were detected. The most common DQA2-allel to be found was D (n = 263), which was also part of the most frequent genotype B1/D (n = 44). 23,4 % of all confirmed allels consisted of a DQA2-allel and an additional DQA2-like sequence. The odds that animals carrying such a duplicated DQA2-haplotype would suffer from footrot were significantly lower than the odds of the ewes lacking the duplication (OR = 1,76, [95%-Confidence Interval: 1,08 bis 2,88], p = 0,02). Comparing single DQA2-allels with each other leads to the result that the likeliness of a footrot-infection is lower for ewes having one of the duplicated allels G and J2 than for the ewes carrying the not duplicated allels E and L (OR L/J2 = 2,09, [95%-Confidence Interval: 1,07 bis 4,10], p = 0,03). The adoption of the ovine DQA2-gene as a marker-gene to estimate footrot-tolerance seems reasonable, taking into account that so far it is the only possibility to determine the susceptibility of individual animals in flocks without clinical signs of footrot-infection. As the tolerance against footrot is connected with a distinct and in relation to the highly susceptible animals long lasting immune response, sustained success could be anticipated by using a combination of specific vaccination and selective breeding.