Metoder för parasitundersökning i fårbesättningar

Abstract: Infection with endoparasites is a problem in sheep flocks worldwide. In order to avoid treating animals with anthelmintics unnecessarily, or missing animal groups in need of treatment, it is important that there are diagnostic tools that effectively detects sheep groups with a high degree of infection. A common way of estimating the degree of infection in sheep farms is to analyze the number of parasitic eggs in samples from a certain number of animals in the flock. The result is then used to estimate the overall degree of infection in the flock. The purpose of this study was first to investigate the distribution of parasitic eggs between the individuals in a relatively small flock of sheep as well as to investigate what endoparasite species were present in the flock. The third, and most important purpose of the study, was to investigate to what extent the number of individual fecal samples included in a composite sample influences the accuracy of the estimation of the flock mean. Material in the form of individual fecal samples were examined from two different sample groups; 60 fecal samples came from Vidilab (a laboratory that routinely examines fecal samples for parasitological analysis) and 49 samples were collected from a hobby flock. In both cases, the individual samples were analyzed with the McMaster method independently, as well as in the form of composite samples that were made up of samples from several individuals per group. The individual samples that were included in the composite samples were sorted both randomly and in different pools consisting of samples with high and low egg counts, respectively. The composition of the parasites in the pool samples was examined using digital droplet (dd) PCR. Finally, a Bootstrap analysis was conducted with data from the different sampling groups to theoretically determine how the egg count result is influenced by different individual numbers that can be included in pooled sampling. This study showed that the range of egg secretion between individual sheep egg was high in both sampling groups. A small proportion of the animals yielded high egg counts while the majority of individuals only excreted small amounts or no parasitic eggs at all. In the ddPCR study, the three most common endoparasites in Swedish sheep herds were detected (Haemonchus contortus, Trichostrongylus spp. and Teladorsagia circumcincta). In addition, the study indirectly showed that there were other Trichostrongyle species in the samples. The Bootstrap analysis showed that the accuracy of the test result increased with the number of individual samples, as shown in previous studies. In summary, this study supports the findings made in previous studies. The test results for examining pool samples are influenced by several factors where the individual number tested is the most important factor in increasing precision.