Since controlling wild horse population was also mentioned in this thread, here is innovative suggestion that I hope will get far more attention soon:
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A former Forest Service supervisor came up with this idea, which is very practical, affordable, easy and humane.
BLM employees can wait at a mustang herd's watering hole, and tranquilize the lead stallion in the herd with a tranquilizer gun. They can then perform a quick, simple, on-the-spot vasectomy. Then, the lead stallion still has full hormone production, and will still lead the herd as before. He will continue to run off most attempts by other stallions to breed the mares, and population growth will be minimized.
Only one horse per herd needs to be sterilized (Very price and time effective). Horses don't have to go through the trauma of being rounded up and corralled. This procedure is reliable and permanent at preventing the horse from reproducing, unlike birth control medicines/patches used for mares (It was reported that in one herd one year, 80% of the mares with foals had previously had birth control administered. If birth control does actually work, it's effectiveness will decrease after the time it's given--maybe last 4 years maximum? I'm told it costs ~$200/mare, also.). The procedure is not risky to the horse's health and horse doesnt need movement restricted during recovery time (unlike the gelding of stallions or spaying of mares). Horses do not have to be slaughtered on an ongoing basis to control numbers. Herds can mostly continue in their normal living patterns and habitats. Selective choices can be made to allow certain stallions and herds to reproduce, if desired, as well.
The man who came up with this idea 30 years or so ago discussed it with "Wild Horse Annie" (who pushed the original legislation protecting wild horses), and she supported its use.
There are viable, wise solutions that can be used to control wild horse numbers.