Aristotle was talking about holism when he said that "the whole is more than the sum of its parts".
Holistic care means that you take into account the physical, mental, and
emotional well being and health when treating or preventing disease. What this
looks like in practice is that you do not just try to fix individual symptoms; look at the individual trees
but don't lose sight of the forest. 
In other words, take a broad view of things.
For example, a horse with ulcers doesn't just need a "band-aid" for the ulcers themselves like a drug or even an herbal remedy. In addition to some kind of treatment they most likely need to be fed more often and have their environment, stress load, show schedule, and training re-evaluated.
The short and simple definition of holistic comes from Websters:
holistic
- 1 : of or relating to
holism
2 : relating to or concerned with wholes or with complete systems
rather than with the analysis of, treatment of, or dissection into parts <holistic
medicine attempts to treat both the mind and the body>
Because of my experiences over the years with my horse Sage, and various other pets, I have come to the conclusion that when it comes to health, you really need to know at least a little bit about a lot of things - as well as have a team assembled of experts in their respective fields. For example, the farrier may point out something that the veterinarian missed (and vice versa), and some people specialize in certain areas that could be helpful to you and your horse. I have learned, though, that relying exclusively on your vet, chiropractor, or farrier or anyone else for a certain problem is usually too narrow a view or path to take - even if they call themselves "holistic" or "natural".
It is the very nature of animals to have internal wisdom about what they need and to then seek that out - be it herbs, minerals, vitamins, rest, or even death. Horses are no exception, and in fact are very good at it; a lot of what we know about herbs came from observing horses (also called herbivores). They listen to their bodies and seek out what they need. You cannot heal your horse (or other pet); they do the work themselves if they have everything that they need. The modern domesticated, stabled horse, however, is severely restricted and incapacitated in their abilities to help themselves.
By building your knowledge base in key areas, you set yourself up to make better decisions about the care of your horse.
Know the horse's nature - its physical make-up, health requirements, and its emotional needs, instincts and ways of communicating. Know the basic principles of holistic care and have some working knowledge of nature's remedies. Finally, know the nature of your own particular horse or horses.Know A Little Wild, Get A Little Balance
When you choose a horse as your pet, your companion, your partner, it is helpful to know at least a little about what that horse would do, be, eat, and have in the wild state - in nature. For example, what would their hooves look like and be able to endure? If you know something about the wild horse, and you know your tame horse (personality and sensitivities, conformation, etc) then it can be easier to figure out what is out of balance and try to bring it back into balance.
You may not be able to give your horse a herd of horses to roam with, over miles of grazing land, but there are a lot of other things that you can do. And while you are doing these things, I have learned that it is vital to give a voice to your gut instincts and not be intimidated by those with higher degrees or more experience.
No one has the same degree of bond with your animal as you do.
Not being intimidated is often easier said than done, but you may save yourself, and your horse, a lot of heartache and disease if you do.
Start Where You Are And Do What You Can
Something to
remember in all this, though, is that it does no good to learn about
natural horse care and then get paralyzed with guilt or feel down in
the dumps about what you have done to your poor animal unknowingly. Nor does it help to become
holier-than-thou with your new-found knowledge and make other people feel guilty
or bad. Start where
you are, and do what you can. (For a related topic, see my article on
boarding.).
Fortunately, you don't have to be a horse in order to have a great relationship with one (but it wouldn't hurt to imagine or think it sometimes). A lot of horse trainers and books will talk about feel, but when it comes to health you really cannot substitute for knowledge. Your instincts will then help you with the direction that you need to take or decisions that you need to make with that knowledge. You are the needle of the compass; you determine the kind of care that your horse gets. This includes coordinating the expertise of veterinarians, farriers, trainers, and anyone else coming in contact with your horse.
I cannot stress enough the importance of assembling a good team of knowledgeable, caring individuals to help you and your equine friends. The AHVMA site is a great resource for an overview on holistic medicine and how to locate a holistic veterinarian.Combining holistic care and concepts with allopathic or traditional care is the basis of integrative medicine. For a good overview of what integrative medicine really entails, check out Dr. Marty Goldstein - What is Integrative Medicine?.
Trust Your Instincts And Never Give Up
Chances are, there is something or someone that you have not tried yet in your quest to solve a health challenge. Not every creature responds to the same medicine or the same approach, and sometimes you just need to try a few different things or combinations of things. And just because it is holistic or natural or alternative doesn't mean that it will necessarily be the answer either.
It is up to you to voice your concerns, pay heed to your instincts, and never give up. Do not be intimidated by degrees, either, because no one has the same degree of experience with or intimate knowledge of your horse as you do...sometimes easier said than done. And finally, trust your guts - your horse does.