(CBS4) – The Bureau of Land Management blames equine influenza for the deaths of 117 horses at a facility in Cañon City. Fifteen horses died between Saturday and Sunday contributing to that death toll.

The illness is hitting the group of wild horses which were rounded up on the Western Slope. The BLM captured more than 1,100 horses last year; 684 came from the Sand Wash Basin and another 457 came from the West Douglas herd.

The Wet Mountains overlook the pens of the East Cañon City Prison Complex. (credit: Mark Neitro, CBS4)

BLM officials say the sick horses were vaccinated within five to 10 days of getting sick.

Some opposed to the roundups are questioning why the horses, which were brought in late last summer, hadn’t already been vaccinated.

“I think if they didn’t have the facility ready to take proper care of them, absolutely they should never have been rounded up,” said Ginger Kathrens, founder of the Colorado Springs-based group, The Cloud Foundation.

The BLM says it is investigating the vaccines now to see if that could have played a role.

“The timing of the vaccination is something that we’re reviewing as we take a look at how we got to where we’re at,” said BLM spokesman Steven Hall.

The agency maintains the horses were in poor health when they arrived.