LAS VEGAS (KLAS) — A roundup of more than 1,000 wild horses has passed the halfway point in northwest Humboldt County.

Bureau of Land Management (BLM) reports show 15 horses have been euthanized — almost all due to blindness or broken legs. One horse was euthanized because of “dental abnormality — severe tooth loss” and another had a deep infection from a previous puncture wound.

The Calico Complex roundup will remove 1,036 wild horses on a 584,101-acre range that has an “appropriate” herd level of 572 to 952, according to the BLM. A count performed by helicopter indicated nearly 1,600 horses were on the range.

So far, 508 horses have been gathered, records show. The BLM says that 40 mares will be treated with fertility control drugs and released back to the herds.

The area includes several mountain ranges including the Black Rock Range, and helicopters are being used to round up the horses. They are being taken to corrals in Fallon — the Indian Lakes Off-Range Corrals — before being prepared for adoption or sale, according to the BLM.

Wild horse roundups have been under scrutiny this year after video showed a foal with a broken leg running from a helicopter. Following that incident, 145 horses died in holding pens in Canon City, Colorado, after equine flu spread.

The BLM says the ranges can’t support the animals, citing deteriorating health conditions in the herds. Wild horse advocates counter that the horses are removed to make room for commercial livestock that grazes on the same land.