A horse of many colors

I have been researching for three solid days a seemingly simple question,
but an outrageously unclear answer.

How is a horse legally defined?

Like The Horse of Many Colors in the Wizard of Oz,
it seems that a horse can be any number of legal definitions,
depending on the facts at hand.

Among the options:

A horse is livestock.
Just like cattle, sheep, pigs, etc.
Except in most states it is illegal to kill them for human consumption.
What makes horses immune from being eaten, but not the others?
Is that fair?

A horse is property.
This is the traditional view.
So if your horse is negligently killed, then you can recover their Fair Market Value at the time of destruction, like your car.
But a horse is not treated legally exactly the same as inanimate property,
so if a horse isn't the same as all other property, then what is it?

A horse is a pet.
This has become the prevailing tradition in California.
Pets have rather strict limitations in California law,
and some cities are elevating the pet status from being "owned" to being "guarded" by their human owners.  This change opens the door for a third party to claim guardianship over your pet,
can limit the veterinary options available, such as humane euthanasia, and can expand the tort recovery for a negligently destroyed pet- perhaps moving into the thousands and millions of dollars in "special damages," similar to recovery if your child or spouse has been killed (though loss of consortium, loss of relationship, etc is not included, but more so, "intrinsic value" grounds are used.)
With such classification should horse slaughter for any purpose be prohibited?
If a pet, can abandoned, retired, or overpopulated horses ever be humanely slaughtered for non-human-food purposes? (For example, horse meat has been found as the best natural-substitute for carnivorous animals in zoos, such as lions)
Can horses be used in medical or scientific research?
Can horses be used as an economic investment if legally considered a pet; will horses be subject to labor laws like humans?


All this confusion requires clarity.
Courts cannot be expected to know how to decide cases with such ambiguity in the law,
and equine participants --as subjects of the law-- require foreseeability of how their behavior will be received by the court system.

I feel horses are a valuable economic force in our nation, and that should not be stripped away from the investors.
I don't believe that horses deserve the same legal protection as humans,
but I do hold a high standard for the ethical treatment and welfare of these beasts under our control (that includes wild horses on Federal land).
I think there would be great loss and great gain to any one of these definitions being the unequivocal final categorization of a horse.
Therefore, the legislature must undertake to more clearly define the equid body of law.
That is no small feat, and would be at great cost.