Ingesting ash may be harmful to livestock, causing abrasion of the teeth, and in cases of high fluorine content, fluorine poisoning (toxic at levels of >100 µg/g) for grazing animals. It is known from the 1783 eruption of Laki in Iceland that fluorine poisoning occurred in humans and livestock as a result of the chemistry of the ash and gas, which contained high levels of Hydrogen Fluoride. Following the 1995/96 Mount Ruapehu eruptions in New Zealand, two thousand ewes and lambs died after being affected by fluorosis while grazing on land with only 1-3 mm of ash fall. Symptoms of flourorsis among cattle exposed to ash Brown-yellow to green-black mottles in the teeth, and hypersensibility to pressure in the legs and back. Ash ingestion may also cause gastrointestinal blockages. Sheep that ingested ash from the 1991 Mount Hudson volcanic eruption in Chile, suffered from diarrhoea and weakness.