State Veterinarian Dustin Oedekoven says officials estimate at least 10,000 to 20,000 head of livestock died in last weekend's blizzard in western South Dakota.
But Oedekoven says those estimates will likely rise as more information is gathered.
Some ranchers in western South Dakota have reported losing 50 percent or more of their cattle.
Oedekoven says officials are compiling numbers of livestock deaths from ranchers, the South Dakota Civil Air Patrol and others.
A relief fund has been set up to help ranchers who have lost livestock.
People who want to donate can go online to "www.giveblackhills.org" and search "Rancher Relief Fund."