Grazing sheep on pastures with tansy ragwort (Senecio jacobaea L.) : results of a two-year study on ingested pyrrolizidine alkaloids and transfer into animal organs

Tansy ragwort (Senecio jacobaea L.) growing in animal pasture may pose a risk to humans due to the potential transfer of pyrrolizidine alkaloids (PAs) into food of animal origin. Here, we investigated what amount of PAs corresponds to the amount of ragwort consumed by sheep on a pasture and whether the ingested PAs are transferred into edible tissue. From 2020 to 2021, a field study was conducted with 70 sheep grazing on a pasture (stocking density of 12 sheep/hectare) with considerable quantities of tansy ragwort. After slaughter, blood samples were taken for analysis of liver enzyme activities and haemoglobin concentration. Samples of ruminal fluid, liver and diaphragm pillar were analysed for PAs. The amount of ingested ragwort was determined by counting missing plant parts and calculating their weight using reference material. The mean daily intake of ragwort per sheep ranged from 0.16 kg to 4.89 kg fresh matter and corresponded to PA doses from 0.3 to 40.9 mg/kg body weight with no effect on the liver enzyme activities. The PA concentrations in the animal tissue were between the limit of detection and a maximum of 8.0 µg/kg in the liver and 2.5 µg/kg in muscle. These data suggest that the risk is negligible of exposure to PAs through consumption of meat or liver.