Grazing Sheep in Organic Vineyards: An On-Farm Study about Risk of Chronic Copper Poisoning

Abstract

Many winegrowers and sheep breeders are interested in wintertime grazing in vineyards, as an agroecological alternative to mowing or herbicide spraying, and additional supply of forage. Still, strong concern is raised by the use of copper-based fungicides, particularly in organic vineyards, since copper is known to induce chronic toxicosis in sheep. We conducted an on-farm study with n = 12 1-year-old Merinos × Mourerous ewes grazing the cover vegetation of vineyard plots during wintertime, in order to check whether this agricultural practice might be harmful to sheep. Our results indicate that most copper found in the cover vegetation originates from fungicide spraying versus plant uptake from the soil, and that rain-induced washing-off and plant growth-triggered dilution of copper are crucial to reach close-to-safe grazing conditions. Furthermore, we found that while sheep remained globally healthy during the 2 months of the experimental period, the plasma activity of Glutamate Dehydrogenase increased by 17.3 ± 3.0 U/L upon vineyard grazing (p < 0.001), reflecting liver storage of copper. We also discovered that the dynamics of molybdenum in sheep plasma are strongly affected by exposure to copper, suggesting a possible adaptation mechanism. Overall, our results suggest that winter grazing of sheep in organic vineyards is reasonably safe, but that care should be taken about grazing period duration. More research should be conducted with respect to long-term copper accumulation, spring and summer grazing, and possible protective mechanisms against copper chronic poisoning.