09/11/2026
Colorado Horse Rescue Network released the below information concerning the aggressive mare (disclaimer this is not our horse or rescue, we have no affiliation, we have been asked to keep our followers updated on the situation):
Test results thus far are strongly suggesting Macy has a granulosa cell tumor. Her testosterone levels are equal to a breeding stallion. Other hormones are also off the charts. This type of ovarian tumor can also cause them to appear physically stallion like including the cresty neck, etc as well as exhibit stallion like behaviors. Regardless, the "stallion-like" attack makes sense. Hating saddles, hating her flank touched, and the sudden fits of rage make sense. The fact that she "used to be" so easy and gentle, and has progressively declined behaviorally. All the puzzle pieces are falling into place. I am so glad we investigated the "why" of this incident. Imagine if we had allowed a trainer to take her thinking she was just spoiled, or sent her to a sanctuary where she was miserable, in pain, and ANGRY. This is exactly why we said no to trainers, sanctuaries, and well meaning individuals. I knew in my gut something was WRONG. What would normally be a pony that was a little spoiled was actually a full on breeding stallion from a hormone standpoint. Speaking with specialists these hormone levels indicate she's been like this for some time though it's impossible to pinpoint. Most mares are diagnosed around 10 years of age.
Why didn't we see this on ultrasound? Because in most cases, the other o***y stops functioning and in her case it was very much still developing follicles. This is an unusual case, thankfully we sent in bloodwork to be certain. This horse has been dealing with hormone levels from THREE TO EIGHT TIMES THE NORMAL RANGE. Not to mention the tumor itself is usually painful for them, resulting in her disliking saddles and being touched in that area. (Extreme hormones in people cause headaches and migraines, not a stretch to think it could in horses)
Now the next big question, do we try to fix it?
This will be one of the most difficult decisions of my career in rescue. Studies show significant behavior changes (many completely eliminating the aggressive behavior) with ovariectomies. There are many many things to consider. We do not have her genetic testing back. Nor metabolic. These are both issues that would give us clear answers on if this is worth taking a chance. Is it worth the risk? Could she return to normal? Could she ever be fully trusted? Even if the surgery was covered and didn't cost the rescue, is this appropriate use of resources? If she is spayed, could we ever adopt her out? I have a million questions in my mind. I've known major successes from this surgery. I know of one that made very little difference. The studies and statistics are on the side of success, but there's absolutely still a risk. I'm thankful that we've got a team to make decisions on this. We still need the last few pieces of the puzzle by way of testing. Donating her to the university for the study is still absolutely an option. Behavioral euthanasia is still absolutely an option, and would NOT BE WRONG. When your job is saving the horses that can be (responsibly) saved, the line blurs from time to time. There's been thousands of mostly great comments. There's been some ugly ones too. That's ok, this is a hot topic and I'm glad you're all along for the ride even if you don't agree with us investigating the cause. And all of you who wanted to crucify the trainer, clearly this was a situation no one could have expected or prepared for. Show some kindness to her previous owner and the injured trainer folks, this is a one in a million situation. (Ok GCL is seen in less than .6% of mares, cases involving extreme aggression account for less than half of those diagnosed, so you do the math). Pray for clarity in moving forward too. This is going to be a weekend of soul searching.
