New research – hope for tick-infested animals

Janne Karin Brodin

Each year animals suffer and farmers lose out due to diseases caused by ticks. A new doctoral thesis shows that this can be counteracted. Researcher Lise Grøva of Bioforsk and UMB is already able to give recommendations to sheep farmers, but calls for more research into the problem.

Lise Grøva Photo: Arnold Hoddevik

“Tick-borne fever in sheep – production loss and preventive measures” is the title of Lise Grøva’s doctoral work at Bioforsk Økologisk and University of Life Sciences (UMB). The work has been carried out in close cooperation with Nofima and Norwegian School of Veterinary Science.

In her scientific articles and her doctoral work, Grøva recommends turning the lambs out on pasture as soon as possible in tick-infested areas. This advice has been given before based on an infection study, where it has been seen that young lambs have been less affected by the disease than older lambs when infected with tick-borne fever. Now, field trials have also shown that lambs turned out on pasture one week after birth had a better growth rate than those who were turned out after three weeks. This may indicate that, in tick-infested areas, it is advisable to plan for a later spring lambing, and to turn the lambs out while they are still very young, says Grøva.

Widespread infection
It is important to take into account the seasonal variations of prevalence of ticks and of the bacteria Anaplasma phagocytophilum, which is transferred with the tick and leads to tick-borne fever in sheep, Grøva says. This variation will probably influence the effect of turning the lambs out soon after birth.

Lambs with tick-borne fever grow slightly slower than healthy lambs, but not as much as one would think, says Grøva.

Based on blood samples from 1208 lambs, she has found that lambs that carry the infection have approximately 3 % lower autumn weight than non-infected lambs.

Tick-borne fever is one of several illnesses in sheep that are transferred through the bite of a tick. In areas where ticks are prevalent, the infection from the “tick-borne fever bacteria” is common: also in herds where the illness is not observed, many lambs may be infected. From previous studies, this is known to be the case also in herds where the lambs are given prophylactic treatment against the bacteria.

More robust
The studies in this doctoral work reveal differences in the reactions of the lambs to the infection.

It may seem that the Old Norse sheep breed reacts differently to the “tick-borne fever bacteria” than the Norwegian White sheep, says Grøva, and adds that more studies need to be done in order to draw any firm conclusions about this. She is also of the opinion that robustness against this disease may possibly be strengthened through breeding, but there is still much to be done also in this area.

We need to do more to identify which sheep are more robust against this disease than other individuals within the same breed. This will give us a foundation for adding this trait to the breeding programs.

Lise Grøva defended her thesis at UMB, Department of Animal and Aquacultural Studies on Friday August 26th 2011.

“An important animal welfare theme, as there is little knowledge on tick-borne diseases” said opponent at the defence Dr. Joanne Conington. She held that Grøva’s study has added to the knowledge in this field, adding that Grøva has used a wide variety of methods and has combined data from different types of studies. In this way, combining competence within varied fields, her study forms a holistic approach.

This doctoral work forms part of the SWATICK project: “Improved welfare in sheep production measures resistance and robustness related to tick-born fever in sheep”. The project has been financed by the Norwegian Research Council, Animalia and Nortura.

The contribution of Lise Grøva at Bioforsk Økologisk brings us one step closer to solving the riddle of tick-borne diseases in sheep.

Updated: 07.09.11
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