Priorities

In general terms large scale disasters can come in many forms, volcanic, earthquake, flooding etc.

The effects on livestock are often very similar and some general precautions apply to most situations.

The effects on livestock will also be dictated by:

time of year
prior condition of livestock
stage of pregnancy
age of stock.

Safety of humans and stock. In cases of flooding move stock to higher ground
Clean water. This is an essential item. Water heavily contaminated with ash or silt is not suitable, especially if stock are grazing silted/ashed pasture and/or eating feed of dubious quality. Remember that troughs that have been contaminated will need draining and cleaning out properly
Feed. Pastures contaminated with silt/ash will have reduced palatability
Physical - depending on particle size, origin, hardness of silt particles and quantity consumed they can act like sandpaper against the rumen wall. Particles can also block up 2nd and 3rd stomachs leading to ketosis, lack of appetite and scouring. Provide plenty of good water and energy to prevent ketosis
Chemical toxicity - possible if contaminants in silt/ash - hard to identify or quantify. Good water and good rumen function hopefully avoids problems
Infectious problems - mainly bacterial. Soil may contain clostridia spores and sewage and effluent contamination may lead to gut diseases such as Salmonella
Increased risk of mastitis from environmental bacteria eg. E.coli
Dead animals in silt e.g. rats etc
Feed value issues - poor energy and nutrient intake, cow dry matter intake poor rumen function, acidosis and ketosis. Direct impact of silt or other nutrients, such as reducing iron and copper uptake.