Rings of the Hoof Wall
This material has been published in extenso previously 1. The main findings are repeated here. Literature review and bibliography may be found in the Anvil report.
The surface of the hoof is characterized by striations running from the coronary border to the bearing surface of the hoof wall and by rings or grooves at right angles to those striations and parallel to the coronary band., Figure 1.
Figure 1: Drawing from Lungwitz with marked rings on the deformed, compressed side of the hoof.
It is well-known that the striations represent the superficial horn tubules of the hoof wall. While the rings or grooves are mentioned and illustrated in many texts, I found only three papers - in German - which discuss the nature and cause of these features.
Sagittal sections of the hoof wall reveal a wavy inward and outward bending of the more superficial horn tubules which correspond to the rings and grooves on the surface of the hoof. Such sections make it quite clear that there is no distinction to be made between ring and groove. The ins and outs are simply the wavy nature of the superficial horn tubules, Figure 2.
Figure2: Photomicrograph with wavy superficial horn tubules. Polarized light about 10x.
It seems clear, or we can at least hypothesize, that this wavy topography is the result of compression of the outer portion of the hoof wall with subsequent buckling of the superficial horn tubules.
Experimental data over many years has shown that compression of the hoof wall does occur and particularly in the proximal portion of the wall close to the coronary band. More recent work has demonstrated the pattern of hydration of the hoof wall, Figure 3. With compression, then, the buckling effect will be most pronounced in the proximal part of the hoof wall where the moisture content is greatest. This is, of course, consistent with the fact that these rings always appear just below the coronary band and proceed distally, toward the ground, as the hoof grows.
Figure3: Drawing from Bertram and Gosline indicating the hydration of the hoof wall from coronary band (above) to bearing edge of the hoof wall (below).
It is clear enough that any factor which causes an increase in the compression loading of part or all of the hoof will increase the prominence of the rings. Some of those factors are discussed in the Anvil Magazine paper, and I'm sure the reader can think of any number of others.
1 Rings of the Hoof Wall of Equids, Anvil Magazine. December, 1999, pp. 24-7.