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article imageStudy: Sheep with parasites reproduce better

By Tim Sandle     Aug 11, 2014 in Science
Researchers have found that an animal's ability to endure an internal parasite strongly influences its reproductive success. The finding could provide the groundwork for boosting the resilience of humans and livestock to infection.
This conclusion has come from a study where scientists examined the relationship between a sheep's body weight and its level of infection by nematodes, tiny parasitic worms that thrive in the gastrointestinal tract of sheep. The level of infection was determined by the number of nematode eggs per gram of the animal's feces.
For the data collection, the researchers used information collected over many years on the Soay sheep living on the island of Hirta, about 100 miles west of the Scottish mainland.
The study found that the degree of weight loss varied widely: an adult female sheep with the maximum egg count of 2,000 eggs per gram of feces might lose as little as 2 percent or as much as 20 percent of her body weight. The researchers then tracked the number of offspring produced by each of nearly 2,500 sheep and found that sheep with the highest tolerance to nematode infection produced the most offspring, while sheep with lower parasite tolerance left fewer descendants.
It is thought that tolerant female animals invest less energy in gut repair which means that they are fitter and stronger, and thus have a better chance at giving birth.
It is hoped that the findings can translate into useful medical advice for people. Medical researchers have long understood that people with similar levels of parasite infection can experience very different symptoms
The study was carried out as a collaboration between Princeton University and the University of Edinburgh. The findings have been reported in the journal PLoS Biology, in a paper titled “Selection on Individual Variation in Tolerance of Gastrointestinal Nematode Infection”.
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