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Capillaria obsignata is, together with Ascaridia galli and Heterakis gallinarum, one of the most common nematode species in chicken. The Department of Animal Sciences, Georg-August-University Göttingen, researches on the genetic resistance against parasites in chicken. Especially studies concerning resistance in chicken against the species A. galli and H. gallinarum have been published before. In order to establish further research projects on Capillaria, the handling and behavior of C. obsignata during incubation and embryonation and the subsequent artificial infection has to be investigated. In the first experiment the in uteri development of non-embryonated C. obsignata eggs in four different incubation media (0.5 % and 2 % formalin, 0.1 % potassium
and 0.1 N sulfuric acid) were compared. The results showed that most of the eggs (> 82 %) in the first two-thirds of uteri in the intact females have the potential for embryonation without being influenced by the incubation media. However, the subsequent disruption of the females by Potters homogenizer to obtain a suspension of the eggs, led to a significant loss of embryonated eggs (< 33 %). For the second experiment an infection of chickens with four different infection dosages (250, 500, 1000 and 2000 eggs) was performed. Prior to use for experimental infection the eggs were incubated in the uteri of the female worms to complete embryonation in the four different media. It emerged that 0.5 % formalin and sulfuric acid which produce eggs with establishment rates of 54 % and 43 %, respectively, can be successfully used as incubation media for C. obsignata eggs, whereas potassium dichromate which produces eggs resulting in an establishment rate of 6.5 %, impairs subsequent infectivity of the eggs (P<0.001). The effects of media on the infectivity of the eggs were confirmed to be fairly repeatable. Noteworthy, no harmful effect of infection was encountered concerning the host animal performance with the infection doses from 250 up to 2000 eggs. In the third experiment the four most prevalent Capillaria species in poultry (Capillaria obsignata, Capillaria bursata, Capillaria caudinflata and Capillaria anatis) were distinguished morphologically. This was followed by a genetic differentiation with the sequencing of the cytochrome c oxidase subunit I (COI) gene of the mitochondrial DNA. A COI fragment of 568 bp (C.o._1) was successfully sequenced for 41 C. obsignata individuals. Another sequence with 433 bp was found in seven C. bursata, five C. anatis, and two C. caudinflata (C.spp._abc_3). Furthermore three C. bursata showed a distinct sequence with 424 bp (C.b._2). Identities among the three different sequences ranged from 81.4 to 84.5 %. The results of the sequence C.spp._abc_3 are to be regarded as questionable, since the species can in general be reliably distinguished morphologically. It thus has to be considered, that the obtained sequences stems from the amplification of pre-amplified DNA i.e. as a consequence of contamination. Further investigations e.g. by sequencing additional genes are needed to clearify this issue.