The agency maintained more than 500 horses could die of dehydration in the next week if the roundup didn't continue. Horse advocates say it's inhumane to herd the animals by helicopter to trap sites in the hot summer temperatures.
U.S. Bureau of Land Management spokesman Doran Sanchez says 54 mustangs were gathered Friday afternoon and another 192 horses were rounded up Saturday.
While most of the animals have been treated for dehydration and water starvation, Sanchez says it's encouraging that other mustangs appear to be drinking water that has been hauled to the range by the agency.
The BLM says four more mustangs died Saturday, bringing to 17 the number of horses that have died since the roundup began last weekend.
