The Bureau of Land Management says four of the animals were euthanized and two others died of unspecified causes.
The agency began rounding up Cliven Bundy's herd earlier this month.
Officials say the cattle was trespassing on federal land and Bundy owes more than a million dollars in grazing fees.
But Bundy says the land is public land, and hundreds from across the nation came to back him up, including armed militia members.
The BLM eventually called off the roundup and gave back the cattle saying it wanted to avoid a potentially violent situation.
But the battle is far from over.
Several protestors remain on Bundy's ranch outside of Las Vegas.
Senator Harry Reid says a federal task force is being put together to address the situation.