Objective—To compare plasma endothelin (ET)- like
immunoreactivity between healthy horses and those
with naturally acquired gastrointestinal tract disorders.
Animals—29 healthy horses and 142 horses with
gastrointestinal tract disorders.
Procedure—Blood samples were collected from
healthy horses and from horses with gastrointestinal
tract disorders prior to treatment. Magnitude and
duration of abnormal clinical signs were recorded, and
clinical variables were assessed via thorough physical
examinations. Plasma concentrations of ET-like
immunoreactivity were measured by use of a radioimmunoassay
for human endothelin-1, and CBC and
plasma biochemical analyses were performed.
Results—Plasma ET-like immunoreactivity concentration
was significantly increased in horses with gastrointestinal
tract disorders, compared with healthy
horses. Median plasma concentration of ET-like
immunoreactivity was 1.80 pg/ml (range, 1.09 to 3.2
pg/ml) in healthy horses. Plasma ET-like immunoreactivity
was greatest in horses with strangulating largeintestinal
obstruction (median, 10.02 pg/ml; range, 3.8
to 22.62 pg/ml), peritonitis (9.19 pg/ml; 7.89 to 25.83
pg/ml), and enterocolitis (8.89 pg/ml; 6.30 to 18.36
pg/ml). Concentration of ET-like immunoreactivity was
significantly associated with survival, PCV, and duration
of signs of pain. However, correlations for associations
with PCV and duration of pain were low.
Conclusions and Clinical Relevance—Horses with
gastrointestinal tract disorders have increased plasma
concentrations of ET-like immunoreactivity, compared
with healthy horses. The greatest values were detected
in horses with large-intestinal strangulating
obstructions, peritonitis, and enterocolitis. This suggests
a potential involvement of ET in the pathogenesis
of certain gastrointestinal tract disorders in horses.
(Am J Vet Res 2002;63:454–458)
Objective—To quantify changes in endothelium-derived factors and relate those changes to various aspects of digital hemodynamics during the prodromal stages of carbohydrate overload (CHO)-induced laminitis in horses.
Animals—20 adult horses without abnormalities of the digit.
Procedures—Digital and jugular venous blood samples were collected at 1-hour intervals (for assessment of endothelin-1 [ET-1] immunoreactivity and measurement of glucose, insulin, and nitric oxide [NO] concentrations) or 4-hour intervals (CBC and platelet-neutrophil aggregate assessment) for 8 hours or 16 hours after induction of CHO-associated laminitis in horses treated with an ET-1 antagonist. Effects of treatment, collection site, and time and the random effects of horse on each variable were analyzed by use of a repeated-measures model. Where treatment and collection site had no significant effect, data were combined.
Results—Compared with baseline values, CHO resulted in changes in several variables, including a significant increase from baseline in digital blood ET-like immunoreactivity at 11 hours; digital blood ET-like immunoreactivity was significantly greater than that in jugular venous blood at 8, 9, 11, and 12 hours. Digital and jugular venous blood concentrations of glucose increased from baseline significantly at 3, 4, and 5 hours; insulin concentration increased significantly at 5 hours; and the number of platelet-neutrophil aggregates increased significantly at 12 hours.
Conclusions and Clinical Relevance—In horses, concurrent increases in venous blood ET-1 immunoreactivity, insulin and glucose concentrations, and platelet-neutrophil aggregates support a role of endothelial dysfunction in the pathogenesis of CHO-induced laminitis.
Objective—To determine and compare the number,
type, location, and distribution of apoptotic epidermal
cells in the laminae of clinically normal horses and
horses with laminitis.
Sample Population—Formalin-fixed samples of digital
lamellar tissue from 47 horses (including clinically
normal horses [controls; n = 7], horses with acute 
and chronic  naturally acquired laminitis, and horses
with black walnut extract-induced  or carbohydrate
overload-induced  laminitis).
Procedure—Blocks of paraffin-embedded lamellar tissues
were stained for DNA fragmentation with the
terminal deoxynucleotidyl transferase-mediated dUTP
nick-end labeling (TUNEL) technique. Differential
immunohistochemical staining for caspases 3 and 14
were used to confirm apoptosis.
Results—The number of TUNEL-positive epidermal
cells per 0.1 mm of primary laminae was significantly
greater in the acute laminitis group than in the other
groups. In the acute laminitis group, there were 17
and 1,025 times as many TUNEL-positive basal layer
cells and keratinocytes, respectively, compared with
the control group. Apoptosis of TUNEL-positive basal
layer cells was confirmed by results of caspase 3
immunohistochemical staining. The TUNEL-positive
keratinocytes did not stain for caspases 3 or 14.
Conclusions and Clinical Relevance—The large
number of apoptotic basal layer cells detected in the
lamellar tissue of horses with acute naturally acquired
laminitis suggests that apoptosis may be important in
the development of acute laminitis. The role of the
large number of TUNEL-positive keratinocytes detected
in the interface of primary and secondary epidermal
laminae of horses with acute laminitis remains to
be elucidated. ( Am J Vet Res 2004;65:578–585)
OBJECTIVE To investigate risk factors for the development of pasture- and endocrinopathy-associated laminitis (PEAL) in horses and ponies in North America.
DESIGN Case-control study.
ANIMALS 199 horses with incident cases of PEAL and 351 horses from 2 control populations (healthy horses [n = 198] and horses with lameness not caused by laminitis ) that were evaluated in North America between January 2012 and December 2015 by veterinarian members of the American Association of Equine Practitioners.
PROCEDURES North American members of the American Association of Equine Practitioners were contacted to participate in the study, and participating veterinarians provided historical data on incident cases of PEAL, each matched with a healthy control and a lameness control. Conditional logistic regression analysis was used to compare data on PEAL-affected horses with data on horses from each set of controls.
RESULTS Horses with an obese body condition (ie, body condition score ≥ 7), generalized or regional adiposity (alone or in combination), preexisting endocrinopathy, or recent (within 30 days) glucocorticoid administration had increased odds of developing PEAL, compared with horses that did not have these findings.
CONCLUSIONS AND CLINICAL RELEVANCE The present study identified several risk factors for PEAL that may assist not only in managing and preventing this form of laminitis, but also in guiding future research into its pathogenesis.