Tick-borne fever in sheep - production loss and preventive measures

Summary

A major challenge in sheep farming during the grazing season along the coast of south-western Norway is tick-borne fever (TBF) caused by the bacteria Anaplasma phagocytophilum, that is transmitted by the tick Ixodes ricinus. The justification for this study is based on our limited knowledge on the effect of A. phagocytophilum infection on indirect losses i.e. reduced weight gain and weaning weight in lambs. Further, there is a lack of efficient and sustainable preventive measures to tick-infestation and TBF which implies a need for new knowledge. Knowledge on the effect of age of lamb to a natural A. phagocytophilum infection and genetic variation in robustness to A. phagocytophilum infection are possible preventive measures that are investigated in this study.
Our findings show that A. phagocytophilum does cause a significant but relatively low reduction in live weaning weight in lambs. Furthermore, the bacteria seem to be widespread in areas with ticks, but its pathogenic effects may be variable. The proposed preventive measures of turning lambs ≤ one week old on pastures in tick infected areas show a potential to reduce indirect losses to TBF in Norwegian sheep farming, bearing in mind that annual and seasonal variations in tick-infestation will influence the effect of this preventive measure. The indications of breed differences as well as an estimated heritability of 0.22 in survival of lambs expected to be exposed to tick-infestation, indicates potential for improving performance on tick-exposed pastures. It is suggested that further studies should be done to identify genetically robust animals.