A few things:
I guess I should have specified by young horse. She was 9. Not really young, but fit, healthy, and with many years ahead.
I was thinking poisonous weed or allergic reaction because of the colic. However, all the horses have been eating round bales from the same place and none of the other horses have had any problems at all. The allergic reaction part would make sense then, but wouldn't that cause diarrhea or something? I know when humans eat something bad or get food poisoning, that diarrhea is usually involved, and many toxic plants I was reading about also cause diarrhea, but she had no irregular stools.
I'm not sure that a brain aneurism would cause a high fever, trachea edema, and would take so long for her to die. I feel like it would have been her acting weird the day before, and the BO would have found her dead the next morning if that was the case.
A lot of her symptoms sound like encephalitis which can be caused by a lot of different things. The vet mentioned rabies and west nile virus as possibilities, but it seems strange that a mosquito would be out in the winter months. It's been really cold and dry.
"In horses that do become clinically ill, the virus infects
The central nervous system and causes symptoms of encephalitis. Clinical signs of encephalitis in horses include
Loss of appetite and depression, in addition to any combination of the following signs: fever, weakness or paralysis
Of hind limbs, muscle fasciculations or muzzle twitching,
Impaired vision, ataxia (incoordination), head pressing,
Aimless wandering, convulsions, inability to swallow,
Circling, hyperexcitability, or coma.
It is important to note that not all horses with clinical
Signs of encephalitis have West Nile encephalitis. Other
Diseases, including rabies, botulism, equine protozoal
Myeloencephalitis (EPM), and other mosquito-borne viral
Encephalitic diseases of horses caused by Eastern, Western,
And Venezuelan encephalitis viruses, can cause a horse
To have symptoms similar to WN"
I guess rabies is pretty rare, but it also sounds like that. The thing about encephalitis is that every cause says "there are many other causes" which means it pretty much could have been anything.
Most important factor to remember is
To think rabies first when dealing
With unexplainable clinical signs.
The most common sign of rabies is
Behavioral changes. The majority of
Horses initially are dull and
Depressed. A low-grade fever usually
Is present along with convulsions,
Increased sensitivity at the site of
Injury, lameness, gnawing the
Affected area and anorexia.
Symptoms usually progress quickly
Over five to seven days resulting in
Recumbency and death. Often rabies
Is not diagnosed upon the initial
Onset of symptoms, as the horse is
Still calm, alert and eating. Of great
Importance in recognizing rabies is
The rapid progression of the disease.
Because the neurological signs
Always progress rapidly with rabies,
Other possibilities should be
Considered if the clinical signs have
Not worsened after a period of five
Here's the thing though, she didn't have any nicks or cuts or anything resembling bite marks. She wasn't gnawing at anything. I guess sometimes horses get bit on the nose by skunks in Missouri sometimes (apparently there are a lot of rabid skunks in Missouri) but I always liked to pet her nose and never noticed any nicks or anything wrong.
I guess it doesn't really matter what killed her because it isn't going to change anything. The vet talked about how even when something is out of our control, it makes us feel like we have control when we know what the reason behind it is.
We buried her next to my BO's horse who had to be put down 2 years ago. I used to ride him when I was leasing horses from her, and he was a sweet horse too. In the spring time we're going to pick a tree or two and plant it between their graves.
My BO has taught me everything I know about horses pretty much. I took lessons from her for 5 years before I started leasing, and then leased for another 2+ years. She's the only horsey friend I have, so I'm lucky that I had her there for help and support.
Thank you to everyone for all the kind words.