Although I have titled this section Transition from Shoes, it can be transition from any kind of pathological condition of the foot. Some of the worst feet I've seen were both shod and barefoot feet. One big block of the healthy foot picture is nutrition. I am not a nutritionist so you will have to find information on that yourself. But what I really want to address is the lack of acknowledgement and recognition of seriously necrotic tissue in feet by "professionals" in the horse industry.
I've got lots of comments on other pages about different problems with transitioning but I will try to condense my thoughts on reviving dead feet.
Please subscribe to The Horse's Hoof and read my latest article, "Transition = Resurrection".
I want to elaborate on that article here.
In the article I talk about the "necrotic burden". In most situations with medically diagnosed necrotic tissue, called "eschar", the treatment is to "debride" or cut away all of the necrotic tissue. The reason this is done is because the eschar tissue is toxic and an impediment to healing. It will harbor infectious organisms like thrush and continually inflames tissues surrounding it. If the eschar tissue is in a bed sore, it is debrided. If it is an extremity, like a finger, it is amputated. Restoring circulation to eschar tissue can be very very toxic! Blood poisoning!
A shod horse has a lot of necrotic tissue in the hoof. The hoof hardens and dries becoming insensitive to ground surface irregularities and point pressure like rocks. The horse looses proprioception and may trip and stumble. This is considered NORMAL and the horse is considered sound when it can't feel it's feet! It may be normal but it is not healthy.
One of the reasons many people decide that their horse can't go barefoot is because they can't ride their horse without him wincing when he steps on a rock. That is why we use boots! We want our horses to have healthy feet but if we don't have the terrain to toughen the feet, we have to protect them.
In my article in THH, I focused on the color of necrotic tissue. I want to clarify any questions of color here on this page.
First, I want to show you a photo of a white hoof with no necrosis.

This is a front foot with a wonderful shape and nice white horn with no necrosis in the frog or sole. Although there is a problem with this hoof; a toe crack, because prior to this first trim, this horse had been frontally loaded. You can see the healthy color of the frog, sole and wall horn. But overall, there is very little contraction, so there is no necrosis in the frog and you can see here what white horn looks like. Compare this white horn to the photo of a contracted white hoof below. This horse was never shod and although his feet were somewhat neglected, they received a trim from an SHP when he was 2 years old and then was trimmed on and off by both it's owner and me. This was my first trim on this horse which was approximately 3 years after the first SHP trim.

This hoof is also a white horned hoof. This horse was shod most of it's life, had foundered and was diagnosed Cushings and IR.
This is a right front and has greater contraction on the inside due to a higher bar. The coffin bone in this foot is more oval with less bone on the inside palmar process so the chances of getting this 20+ year old horse to grow a new less contracted palmar process at his age is impossible. The only thing a rehabilitative trim can really do is restore blood flow to the coriums growing the horn. What I talked about in my THH article was the eschar (necrotic) tissue. This takes some time and effort to restore to health. It's obvious this necrotic tissue exists in the frog but as I described in my article, the "necrotic burden" includes deeper tissues of bone, vascular and connective.

Still some abscess exits and poor tissue growth in the central sulcus but over all, pretty good progress with very little rehab effort other than trims every 6 weeks.

Also a right front, this foot is considerably more contracted even than the one above. I have highlighted areas that would be trimmed in order to attempt to return blood flow to this hoof. But in my experience, this hoof is almost too far gone, too much dead tissue and too much deformation of the coffin bone to bring back without many other considerations.

Even the foot above has more health than this foot. Note all the black necrotic tissue and almost no frog. This is also a white foot.
One of the reasons why a shod horse can be ridden on gravel or other rough trails is due to the fact that he cannot feel his feet. With all of the blood squeezed out for years and a build up of old horn, the feet are more than numb, they are dead. As long as they remain shod, the horse may live for a long time with no apparent problems. But damage is being done all the time. The worst damage comes when the shoes come off and the hoof is trimmed for blood flow. Horses can literally die from having their shoes removed and having their feet trimmed due to the toxins of all the dead tissue. When the feet are trimmed to allow blood flow to enter, toxins stream into the system and can cause kidney or liver failure. (phot courtesy of Anne Coley)

We've all had a finger get banged and turn black. Very often the fingernail will fall off. The nail bed eventually grows a new nail. This is not unlike the horse's hoof when an abscess is under the wall.. But a shod hoof has much more significant damage than this. A horse with feet like the above horse would be more like a person with severe frost bite!