The research also revealed that the higher worm counts in reproducing females in spring led to the animals having lower body weight in summer – and ultimately they were less likely to survive over the winter, to breed again in the future.
Dr Adam Hayward, a former Impact Research Fellow at Stirling and now a Research Fellow at the Moredun Research Institute, is senior author on the study.
He said: “We’ve known for a long time that reproduction can affect survival.
“Our new study provides an explanation for why this might be the case: we’ve discovered a complex but clear pathway linking reproduction to increased infections and reduced survival.”
The research, Survival costs of reproduction are mediated by parasite infection in wild Soay sheep, is published in Ecology Letters. Dr Luc Bussière, of the Faculty of Natural Sciences at Stirling, is a co-author on the paper.