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Abstract

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.

Full access
in American Journal of Veterinary Research

Abstract

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 [4] and chronic [7] naturally acquired laminitis, and horses with black walnut extract-induced [11] or carbohydrate overload-induced [18] 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)

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in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of clenbuterol, at a dosage of up to 3.2 μg/kg for 14 days, PO, on skeletal and cardiac muscle in healthy horses undergoing treadmill exercise.

Animals—12 healthy horses from 3 to 10 years old.

Procedures—Horses were randomly assigned to a control group (n = 6) or clenbuterol group (6) and received either saline (0.9% NaCl) solution or clenbuterol, PO, every 12 hours for 14 days. Horses were subjected to submaximal treadmill exercise daily during treatment. Muscle biopsy specimens were collected before and after treatment for determination of apoptosis. Echocardiographic measurements, serum clenbuterol and cardiac troponin I concentrations, and serum activities of creatine kinase and aspartate aminotransferase were measured before, during, and after treatment. Jugular venous blood samples were collected every 3 days during treatment. Echocardiography was repeated every 7 days after beginning treatment. Response variables were compared between treatment groups and across time periods.

Results—No significant effect of clenbuterol or exercise on response variables was found between treatment and control groups at any time point or within groups over time.

Conclusions and Clinical Relevance—Results did not reveal any adverse effects of treatment with an approved dose of clenbuterol on equine cardiac or skeletal muscle in the small number of horses tested.

Full access
in American Journal of Veterinary Research

Abstract

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 [153]) 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.

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in Journal of the American Veterinary Medical Association