Relationships between sheep nematode infection, nutrition, and grazing behavior on improved and semi-natural pastures

Gastrointestinal nematodes (GINs) are key parasites of grazing sheep worldwide. To understand the factors influencing GIN infections, we examined the relationships among infection and nutrition, foraging behavior, and animal performance. Further, the parasitism and nutrition of sheep between improved and semi-natural pastures in Japan were compared. Sheep were grazed for 1 month each, first on an improved and then on a semi-natural pasture. Afterward, vegetation surveys, forage analyses, and (plant) nematode larval counts were conducted in both pastures, and fecal egg counts, biochemical analyses, and bite counts were completed for each sheep. The semi-natural pasture had diverse plant species, though it contained less crude protein, and nematode larvae were rarely observed on bamboo. Consequently, fecal egg per gram decreased after grazing on the semi-natural pasture. White blood counts, hematocrit, and glucose also decreased and body weight increased after grazing on this pasture. Principal component and correlation analyses revealed a significant relationship between GIN infection and behavior, but not between nutrition and either behavior or infection. As parasitized animals may become more aggressive feeders to compensate for their reduced nutritional uptake, grazing sheep on semi-natural pastures may facilitate more stable performance due to the lower risk of nematode infection from wild plants.