Thirty five mares will be returned to the HMA on November 16, according to a BLM news release.
The announcement said they were treated with a fertility control drug but did not specify the type.
The gather page said they would receive GonaCon Equine, which may act as a sterilant with a single dose.
The advocates generally oppose the use of the substance but they strongly support the Montana Solution, which can achieve the same results in as little as five doses (primer plus four boosters).
Mares thus treated, no longer able to conceive, are described as “self-boosting.”
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Western Horse Watchers Association 