The Timeline of Laminitis
What happens within the foot of a laminitic horse? We know that the coffin bone can sink or rotate within the foot of a horse with severe laminitis, but that’s fairly late in the game. Researchers are very interested in what happens earlier than
- Topics: AAEP Convention, Article, Laminitis (Founder)
What happens within the foot of a laminitic horse? We know that the coffin bone can sink or rotate within the foot of a horse with severe laminitis, but that’s fairly late in the game. Researchers are very interested in what happens earlier than that–in what microscopic changes take place before there is enough damage to destabilize the coffin bone. Understanding these changes can help researchers investigate how to prevent those changes and hopefully prevent this painful disease.
At the 52nd annual American Association of Equine Practitioners convention, held in San Antonio, Texas, Andrew van Eps, BVSc, MACVSc, a resident at the University of Pennsylvania, discussed a study of findings in this area. Presenting a paper authored by Emma L. Croser, BSc, BVM&S, MVSt, of the University of Queensland (UQ), Australia, and Christopher Pollitt, BVSc, PhD, director of the Australian Equine Research Laminitis Unit at UQ (who were unable to attend the convention), he described what changes researchers saw in serial hoof biopsies taken from horses in which laminitis had been induced.
Laminar Microanatomy
A horse’s hoof is held onto the coffin bone, or the last bone on the end of his leg, by around 600 interlocking, vertical, leaf-like projections called laminae, or more specifically primary epidermal laminae (PEL), van Eps described. Each of those PEL has up to 200 smaller laminae of its own, called secondary epidermal laminae or SEL. These laminae interlock with the same arrangement of laminae on the inner or hoof side of the attachment; these laminae are termed the primary and secondary dermal laminae (PDL and SDL). The laminar system provides about a square meter of attachment area for each hoof.
The basement membrane is a sheet of connective tissue that lines every nook and cranny of the epidermal laminae of the hoof wall, he went on. It is “a key component” of the hoof-bone attachment, he noted.
Timeline of Laminar Changes with Laminitis
The current study evaluated laminar structure with hoof biopsies (punch samples) taken every six hours for 48 hours after induction of laminitis with carbohydrate overload, van Eps reported. Five adult Standardbred horses with no evidence of hoof disease were studied. Changes in the size, shape, and integrity of the laminae and basement membrane (BM) were found as follows:
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Control horses (no laminitis) Biopsies were normal throughout the 48-hour study period. Secondary epidermal laminae were club-shaped with rounded tips that were never tapered or pointed. They showed a uniform length and angle relative to their PEL. The BM was tightly adhered to the SEL, penetrating deeply into the crevices (also called crypts) between adjacent SEL. | ||
 Laminitic horses–12 hours after laminitis induction Two of the five horses showed mild microscopic changes; SEL were narrower and elongated, with more pointed tips and more rounded cell nuclei (which normally are oval and oriented perpendicular to the length of the SEL). The basement membrane appeared to have less integrity at the bases of the SDL. Changes tended to occur only on one side of PEL. “This seems to be the localized nature of early disease change and is most likely reflects higher weight bearing on the affected side,” notes Croser. “At 12 hours, rounding of SEL cell nuclei is the first observable change,” van Eps commented. | ||
 18 hours By this time, separation of the BM from the tips of SEL began in the two horses already showing changes, he reported; these separations resulted in teat-shaped, empty pockets of BM. The BM had even less integrity at SEL bases, and in some cases disappeared entirely. Changes were still primarily limited to one side of the PEL. The SEL were thinner and more elongated with more pointed tips, due to stretching as they weakened. The cell nuclei of more SEL were more rounded, and one of the horses was clinically lame. The SDL also became thinner, and appeared to be pulling away from SEL bases. One additional horse showed the mild changes seen at 12 hours in the other two horses showing signs. | ||
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24 hours The two horses affected earliest showed progressive worsening of tissue architecture, with changes no longer restricted to one side of the PEL. Secondary epidermal laminae were more elongated, their angles relative to their PEL were more acute, and there were many more rounded nuclei. “There was more loss of BM from crypt-type areas; this is probably one of most telling signs,” van Eps said. Two horses still showed no changes, while the later-affected horse showed some worsening of laminar architecture comparable to 18-hour samples of the first two horses Create a free account with TheHorse.com to view this content.TheHorse.com is home to thousands of free articles about horse health care. In order to access some of our exclusive free content, you must be signed into TheHorse.com. Start your free account today!Already have an account?
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 Written by: Christy M. West
Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.
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