The horses seized are said to be either feral or belong to residents who lack grazing permits or have more horses than their permits allow.
Grazing official Wilbur Murphy said horses unclaimed by residents will be sold to a buyer either for resale off the reservation or for transport to Mexico for slaughter for meat.
The Navajo Nation has voiced support for a plan by a Roswell company, Valley Meat Co., to begin slaughtering horses for meat.
A spokesman for Navajo President Ben Shelly has said the reservation can no longer support the estimated 75,000 feral horses that are drinking wells dry and causing ecological damage to the drought-stricken range.
The Navajo Nation Council has approved $3 million in emergency funds to combat extreme drought conditions on the reservation and nearly $1.4 million in additional funds for feral horse roundups.
Leonard Butler, a tribal Natural Resources law enforcement official, said tribal chapters that approved resolutions to conduct the horse roundups in their communities will be compensated with about $20 per head.
"That's the incentive for the chapter to pass resolution to participate in the roundup," Butler said.
Ranger Lorenzo Lapahie said horses that are branded will be kept for three days to give owners time to reclaim the animals by showing a grazing permit and proof of ownership.
Valley Meat's plan has sparked a national debate about whether horses are livestock or companion animals and how best to deal with the tens of thousands of wild, unwanted and abandoned horses across the country.
Horses were slaughtered domestically for decades until Congress cut funding for inspections for horse plants in 2006. That funding was restored in late 2011.