Bob Childs - ESA/AHA/PHCP Certified Hoof Specialist
Endotoxemia and the roll of ET-1 in acute Laminitis
"Although administration of a low-dose of endotoxin to horses causes a
significant decrease in laminar perfusion and digital blood flow, there
have been no repeatable models of endotoxemia that consistently induces
acute laminitis. However, diseases that are often complicated by
laminitis are accompanied by endotoxemia (intestinal strangulating
obstruction, anterior enteritis, enterocolitis, pleuropneumonia, and
metritis). In a study in our laboratory, we demonstrated a significant
decrease in digital arterial blood flow from 30 min to 2 h after
administration of a low dose (35 ng/kg over 30 min) of endotoxin to
conscious horses. There was a concomitant decrease in digital arterial
blood pressure from 30 min to 1.5 h after endotoxin infusion. These
digital hemodynamic effects were accompanied by a significant increase
in cephalic venous plasma ET-1 concentrations. These findings suggest
that perhaps endotoxin does play a role in initiation of the early
hemodynamic alterations in laminitis, and that this may be at least
partly mediated through increased synthesis and release of ET-1."
Authors: Susan C. Eades, DVM, PhD; Ashley M. S. Holm, DVM; and Rustin M. Moore, DVM, PhD
says: "As with humans, diet and exercise are the only way that insulin
resistance, which causes high levels of circulating insulin, can be
Read the article: Laminitis: New Study on Sugar and Starch as a Cause
Article by: Philip J. Johnson, BVSc, MS, MRCVS, DACVIM
Affected horses tend to be aged between 6-to-20 years and there does not
appear to be a sex predilection. The problem is reported more commonly
in some pony breeds, domesticated Spanish mustangs, Peruvian Pasos, Paso
Finos, European Warmbloods, American Saddlebreds, and Morgan horses.
Affected horses are commonly obese and develop excessive adiposity at
specific locations, especially in the crest of the neck, at the
shoulders, above the gluteal muscles, and in the sheath (geldings).
Female horses are notoriously difficult to breed and exhibit abnormal
ovarian cycling behavior. Horse owners refer to many of these horses as
"easy keepers" and vigorously contend that all efforts to reduce the
horse's obesity by dietary restriction are futile. Ample intra-abdominal
(omental) adiposity is evident during ultrasonographic examination of
the abdomen or at necropsy of affected horses.
Many of these horses are presented to veterinarians for diagnosis of lameness attributable to laminitis. There is a very strong association between the development of obesity, metabolic syndrome and the risk for developing laminitis. Commonly, at initial veterinary examination, there already exists both physical and radiographic evidence for long-standing laminitis in these horses although reputable and credible owners and managers report that there have been no prior signs of laminitis or any obvious explanation. Metabolic syndrome is often recognized incidentally when horses are presented for other reasons, such as routine health care or other medical problems. In these horses, visible changes in the hoof that are commonly attributable to laminitis (including prominent growth lines, palmar divergence of growth lines, and a convex sole) may be evident in the absence of laminitic pain or any history of laminitis or lameness. There are minimal hematological changes in horses affected with metabolic syndrome (unless laminitic pain is prominent). Abnormal results of routine serum biochemical profiling might include a slight-to-moderate elevation in the glucose and triglyceride concentrations.
Interesting comments on laminitis and obesity by Donald M. Walsh, DVM
"Based on my experience observing laminitic horses over the past 36
years in veterinary practice, I believe that obesity leads to the
development of weakened laminae and other supporting structures of the
foot and to changes in the growth pattern of the feet. 2 Radiographs
reveal that the appearance of the laminae begins to change in horses
that are becoming obese, even before any signs of lameness from
laminitis are observed.
Perhaps, when a horse becomes obese, there is a messenger substance that
promotes or allows for the skin's basement membrane to stretch so the
skin can "enlarge itself" in order to accommodate for the increased
layer of fat under the skin. If this is so, perhaps this same messenger
substance is also recognized by the epithelial laminar basement membrane
in the foot, which would cause the basement membrane to stretch, which
could result in the weakening of the laminae of the foot in the obese
horse. These weakened feet are much more susceptible to grass laminitis
and other predisposing insults known to cause laminitis.
Obese horses need a major change in lifestyle in order to become healthy. Accomplishing this can be a challenging task for the owner because weight reduction in these horses requires a low caloric diet together with a considerable amount of exercise. Many of the horses experiencing laminitis are so sore-footed that much exercise is not possible. Many live lives of constant pain associated with ongoing bouts of laminitis, which finally results in so much damage to the feet that recovery is impossible. These (heavy-type) horses are the most common group associated with the ingestion of grass as a cause of laminitis."