Less healthy sheep avoid high-quality vegetation due to ticks, study finds

Sheep wait in a pen before being driven across London Bridge Freemen of the City of London as they take up the historic entit
Sheep wait in a pen before being driven across London Bridge Freemen of the City of London as they take up the historic entitlement.

Sheep know the grass is not always greener when it comes to their health, according to scientists.

Less healthy sheep avoid high-quality vegetation due to a higher prevalence of ticks, unlike healthier animals.

Scientists at the University of Bristol used remote GPS trackers to monitor the foraging patterns of 23 sheep on Dartmoor.

They integrated the 114,093 location recordings with satellite data of vegetation quality, field sampling data of tick prevalence, and parasite load and health measures for each sheep.

The most common tick inhabits dense matted vegetation in which humidity and warmth are sufficient and relatively stable.

In their quest for hosts, ticks climb up vegetation and attach to an animal as it passes by.

These can be particularly detrimental for animals as heavy tick infestations can cause significant blood loss.

Lead author Caroline Liddell, a PhD student at the university’s School of Biological Sciences, said: “Discovering that the trade-off between maximising forage intake and minimising parasite encounter depends on the health status of individual sheep emphasises the need to study livestock as individuals, even in group-living animals such as sheep.

“GPS tracking technology provides a feasible and increasingly affordable means of obtaining such individual-level data.

“Our study, which used extensively grazed sheep as a model system, opens new possibilities to study free-living grazing systems, and illustrates the benefits of using GPS technology to advance our understanding in this area.

“Future studies could use controlled interventions, such as antiparasitic treatment, to separate cause and effect and develop understanding of the processes generating the observed associations.”

The study – Response to resources and parasites depends on health status in extensively grazed sheep – is published in the journal Proceedings of the Royal Society B.

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