(Reuters) — Donations of money and some cattle have been rolling in for South Dakota ranchers after a blizzard last week killed tens of thousands of cattle in one of the state's worst agriculture tragedies, state officials said on Thursday.

Dozens of minimum-security prison inmates were aiding the cleanup effort, gathering debris in three towns in the western part of the state hit by record snowfall that felled trees and knocked out power lines.

"This is a very tough time in western South Dakota. Many ranchers suffered devastating losses putting them in an unthinkable position," South Dakota Gov. Dennis Daugaard said in a statement to Reuters.

Between 15,000 and 30,000 cattle were estimated to have perished in the storm, according to South Dakota state veterinarian Dustin Oedekoven.

Animals suffocated as 4 feet of snow piled up. Others suffered from hypothermia, fell off rocky ledges or were hit by vehicles as they wandered into roadways in the blizzard.

The deaths are expected to result in tens of millions of dollars in lost income for ranchers, as they were ready to sell young calves, valued at $800 or more. Also perishing were cows pregnant with calves that would have been born in the spring.

South Dakota in January had 3.85 million head of cattle, the sixth-largest herd in the United States, according to the U.S. Department of Agriculture.

So far, more than $190,000 was donated to the South Dakota Rancher Relief Fund, said Regina Jahr, executive director of the Black Hills Area Community Foundation, which is administering the aid.

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The CHS Foundation — the charity arm of the largest U.S. farm cooperative CHS Inc. — donated $100,000 while $70,000 was pledged online from people across the United States and Canada, Ms. Jahr said.

"Ranchers across western South Dakota suffered significant loss of cattle, sheep and other livestock as a result of this storm, the vast majority of which is not covered by insurance or other programs," CHS Foundation President William Nelson said in a statement.

The Black Hills group was meeting on Thursday with other agencies, including local arms of the American Red Cross and United Way, to determine how to administer the aid, Ms. Jahr said.

With the cattle spread out over a wide expanse of pastureland, it could be weeks or months before a final tally of the dead is available.

Ranchers were also seeking donations of pregnant cows as well as heifers of breeding age for help in rebuilding their herds.

About 60 inmates of the South Dakota Department of Corrections were cleaning up tree branches in Rapid City, Spearfish and Sturgis this week, according to department spokesman Michael Winder.

Parts of Colorado and Wyoming saw heavy snowfall during last week's storms that also brought more than a dozen of tornadoes to Iowa and Nebraska, injuring at least 15 people, damaging homes and knocking down power lines.