When ashfalls destroy pastures, livestock need to be supplied with all of their feed in order to survive in the short-term. The supply of dry feed must be maintained until the livestock are either evacuated or slaughtered, or pasture is re-established. This is very expensive to sustain for long periods of time and access for additional feed to be delivered may be reduced.
Even with very light ashfalls that do not destroy existing pastures, animals may need to be provided with uncontaminated feed. For example, if the ash contains a high level of fluorine adsorbed onto the tiny particles and livestock consume both ash and fluorine, there is a risk of fluorosis.
Livestock near Ruapehu volcano were affected by fluorosis when grazing grass contaminated by ash from the 1995-96 eruptions—more than two thousand lambs and ewes died after eating ash-contaminated pasture. The first sheep deaths began nine days after 1-3 mm of ashfall, and continued for 7-10 more days.