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Objective—To determine effects of age and pituitary pars intermedia dysfunction (PPID) on corneal sensitivity in horses.

Animals—20 adult horses allocated into 3 groups (PPID group, old [> 15 years old] horses with PPID [n = 5]; old group, old [> 15 years old] horses without PPID [9]; and young group, young [≤ 10 years old] horses without PPID [6]). All horses with PPID had hirsutism and abnormal fat deposition or laminitis; none of the old or young horses had hirsutism, abnormal fat deposition, or laminitis.

Procedures—A Cochet-Bonnet aesthesiometer was used to measure the corneal touch threshold (CTT) in both eyes of each horse. The nylon monofilament was applied at a maximum length of 60 mm to the central region of the cornea and length was decreased by 5-mm increments until a consistent blink response was elicited. Tear production was assessed in all eyes via the Shirmer tear test (STT).

Results—Mean ± SD CTT was significantly greater for young horses (47.50 ± 4.52 mm) than for horses in the old (28.06 ± 5.72 mm) and PPID (21.5 ± 3.37 mm) groups. Old horses had significantly higher CTT values than did horses with PPID. The STT values were within the reference range for all groups and did not differ significantly among groups.

Conclusions and Clinical Relevance—Corneal sensitivity decreased with both age and PPID. Because decreased corneal sensitivity is associated with impaired wound healing, increasing age and PPID may increase the risk for nonhealing or recurrent corneal ulcers in horses.

Full access
in American Journal of Veterinary Research


Objective—To evaluate risk factors associated with development of catheter-associated jugular thrombophlebitis in hospitalized horses.

Design—Retrospective case-control study.

Animals—50 horses with thrombophlebitis and 100 control horses.

Procedure—Medical records from 1993 through 1998 were searched for horses with thrombophlebitis. Horses that were hospitalized for at least 5 days, had an IV catheter placed in a jugular vein (other than for solely anesthetic purposes), and had no evidence of thrombophlebitis during admission or hospitalization were chosen as controls. Signalment, history, clinicopathologic findings, primary illness, and treatment were obtained from the medical records. Data were analyzed by use of logistic regression to perform univariate and multivariate analyses.

Results—For a horse with endotoxemia, the odds of developing thrombophlebitis were 18 times those for a similar horse without endotoxemia. For a horse with salmonellosis, the odds of developing thrombophlebitis were 68 times those for a similar horse without salmonellosis. For a horse with hypoproteinemia, the odds of developing thrombophlebitis were almost 5 times those for a similar horse without hypoproteinemia. For a horse in the medicine section, the odds of developing thrombophlebitis were 16 times those for a similar horse in the surgery section. For a horse with large intestinal disease, the odds of developing thrombophlebitis were 4 times those for a similar horse without large intestinal disease. For a horse receiving antidiarrheal or antiulcerative medications, the odds of developing thrombophlebitis were 31 times those for a similar horse not receiving these medications.

Conclusions and Clinical Relevance—Results indicated that patient factors, including large intestinal disease, hypoproteinemia, salmonellosis, and endotoxemia, were associated with development of catheter-associated thrombophlebitis in horses. (J Am Vet Med Assoc 2005;227:1134–1141)

Full access
in Journal of the American Veterinary Medical Association


Objective—To compare the effect of thyrotropin-releasing hormone (TRH) administration on endogenous ACTH concentrations in healthy horses and those with pituitary pars inter-media hyperplasia and compare the test with the dexamethasone suppression test (DST).

Design—Prospective case series.

Animals—15 horses with clinical signs of pituitary pars intermedia dysfunction (PPID), 4 horses with equivocal signs of PPID, and 29 horses without signs of PPID.

Procedures—ACTH concentrations prior to and after administration of TRH were measured 61 times in 48 horses. Results of the DST (cortisol response) were compared with those of the TRH test in 29 horses. Thirty-three horses (24 with no clinical signs of PPID, 5 with clinical signs of PPID, and 4 with equivocal clinical signs of PPID) were euthanized and necropsied and their pituitary glands evaluated.

Results—ACTH concentrations increased in all horses, but magnitude and duration of increase were significantly higher in horses with PPID. Endogenous ACTH concentrations were influenced by season. The ACTH baseline concentrations and response to TRH were not correlated with results of the DST. Results of DST were abnormal only in clinically abnormal horses or those with pars intermedia hyperplasia, but were within reference range in 17 of 26 tests in these horses.

Conclusions and Clinical Relevance—The ACTH response to TRH is a useful test for diagnosis of pituitary gland hyperplasia, particularly in horses in which baseline ACTH concentrations are within reference range. The DST was specific but not sensitive and was inconsistent for individuals, and results often did not agree with the TRH test response.

Full access
in Journal of the American Veterinary Medical Association


Case Description—A 12-year-old Thoroughbred was examined because of signs of depression, neck stiffness, and poor performance.

Clinical Findings—Physical examination revealed that the horse was dull, appeared depressed, was reluctant to raise its neck and head above a horizontal plane, and had a temperature of 38.5°C (101.3°F). No radiographic or scintigraphic abnormalities of the neck were found; however, high plasma fibrinogen concentration and relative lymphopenia were identified and the horse was seropositive for antibodies against Borrelia burgdorferi. Analysis of CSF revealed neutrophilic inflammation, and results of a PCR assay of CSF for B burgdorferi DNA were positive. Immunologic testing revealed severe B-cell lymphopenia and a low serum IgM concentration consistent with common variable immunodeficiency.

Treatment and Outcome—The horse responded well to do×ycycline treatment (10 mg/kg [4.5 mg/lb], PO, q 12 h for 60 days) and returned to normal exercise. However, 60 days after treatment was discontinued, the horse again developed a stiff neck and rapidly progressive neurologic deficits, including severe ataxia and vestibular deficits. The horse's condition deteriorated rapidly despite IV oxytetracycline treatment, and the horse was euthanatized. Postmortem examination revealed leptomeningitis, lymphohistiocytic leptomeningeal vasculitis, cranial neuritis, and peripheral radiculoneuritis with Wallerian degeneration; findings were consistent with a diagnosis of neuroborreliosis.

Clinical Relevance—Nervous system infection with B burgdorferi should be considered in horses with evidence of meningitis and high or equivocal serum anti-B burgdorferi antibody titers. Evaluation of immune function is recommended in adult horses evaluated because of primary bacterial meningitis.

Full access
in Journal of the American Veterinary Medical Association


To evaluate results of cytologic examination of specimens obtained by means of tracheal washes (TW) in 42 horses with a history of poor performance.


Cross-sectional case series.


42 horses with a history of poor performance.


A TW was performed via endoscopy before and after horses exercised on a high-speed treadmill, and specimens were evaluated microscopically and graded.


Ten (24%) horses were considered to be clinically normal before and after exercise. Pulmonary hemorrhage was diagnosed in 8 (19%) horses. One horse had evidence of exercise-induced pulmonary hemorrhage (EIPH) before exercise and pulmonary hemorrhage and allergic or inflammatory airway disease (IAD) after exercise. Five (12%) horses had IAD, and 1 had IAD and pulmonary hemorrhage after exercise. Seven (17%) horses had evidence of EIPH and IAD in both specimens. Four (10%) horses with EIPH had an increase in the proportion of hemosiderophages in the specimen obtained after exercise. Specimens obtained before exercise in 6 (14%) horses were not representative of the respiratory tract and could not be compared with specimens obtained after exercise.

Clinical Implications

Interpretation of TW specimens obtained before and after exercise differed for only 5 of 36 (14%) horses. Specimens obtained after exercise were more likely to reveal airway disease. All specimens obtained after exercise adequately represented the respiratory tract, whereas 6 specimens obtained before exercise did not. Specimens obtained after exercise contained more airway secretions and had less cytologic evidence of pharyngeal contamination. Therefore, we recommend that TW samples be obtained after exercise in horses. (J Am Vet Med Assoc 1999;214:673–677)

Free access
in Journal of the American Veterinary Medical Association


Objective—To determine sensitivity of equine skeletal muscle to tetrodotoxin and compare that with sensitivity of murine and human skeletal muscles.

Sample Population—Semimembranosus, vastus lateralis, triceps brachii, and masseter muscle specimens from 22 euthanatized horses, vastus lateralis muscle biopsy specimens from 25 clinically normal humans, and diaphragmatic muscle specimens from 6 mice.

Procedure—Electrically elicited twitch responses were measured in muscle specimens incubated in medium alone and with tetrodotoxin (100 nM, 400 nM, 1.6 µM for equine specimens and 100 nM, 200 nM, 400 nM, 800 nM, 1.6 µM for murine and human specimens). Percentages of tetrodotoxin-sensitive and -resistant sodium channels were determined and compared among muscles and species.

Results—2 sodium channels with different sensitivities to tetrodotoxin were identified in equine muscle. One was blocked with 100 nM tetrodotoxin and the other was unaffected by tetrodotoxin at concentrations up to 1.6 µM. The only difference detected among the 4 equine muscles was that masseter muscle specimens had a higher percentage of tetrodotoxin- sensitive channels than triceps brachii muscle specimens. Tetrodotoxin-resistant sodium channels constituted 31 to 66% of the equine muscle twitch response, which was greater than that determined for normal human and murine muscle (< 5%).

Conclusion and Clinical Relevance—Equine skeletal muscle contains a high percentage of tetrodotoxin-resistant sodium channels. The 4 equine muscles evaluated were more similar to each other than to murine and human muscles. Shifts in expression of sodium channel subtypes may play a role in the manifestation of certain myopathies. (Am J Vet Res 2000;61:133–138)

Full access
in American Journal of Veterinary Research


Objective—To evaluate the correlation between plasma α-melanocyte-stimulating hormone (α-MSH) concentration and body mass index (BMI) in healthy horses.

Animals—82 healthy horses.

Procedure—Plasma α-MSH concentration was determined by radioimmunoassay. At the time blood samples were collected, body condition scores (BCS) were determined and measurements of girth circumference, body length, and height were obtained. Weight was estimated by use of the following formula: estimated weight (kg) = [girth (cm)2 × length (cm)]/11,877. Body mass index was calculated as estimated weight (kg)/height (m)2.

Results—A correlation was found between BMI and BCS (r s = 0.60 [95% confidence interval (CI), 0.44 to 0.73]). A weak correlation was found between plasma α-MSH concentration and BMI (r s = 0.25 [95% CI, 0.03 to 0.45]) and BCS (rs = 0.26 [95% CI, 0.04 to 0.46]). A correlation was found between plasma α-MSH concentration and BMI in horses ≥ 10 years old (r s = 0.49 [95% CI, 0.20 to 0.69]) but not in horses < 10 years old (r s = –0.04). Horses in the upper quartile of BMI had significantly greater plasma α-MSH concentration (median, 9.1 pmol/L; range, 2.0 to 95.3 pmol/L) than horses in the lowest quartile of BMI (median, 7.0 pmol/L; range, 3.6 to 15.7 pmol/L).

Conclusions and Clinical Relevance—A correlation exists between plasma α-MSH concentration and BMI in horses. Further study is required to determine whether melanocortin receptor defects underlie this correlation or, alternately, whether plasma α-MSH concentration is simply a correlate of adiposity. (Am J Vet Res 2004;65:1469–1473)

Full access
in American Journal of Veterinary Research


Objective—To determine prevalence and clinical features of pituitary pars intermedia dysfunction (PPID) in horses with laminitis.

Design—Case series.

Animals—40 horses with laminitis.

Procedures—Horses with laminitis that survived an initial episode of pain and were not receiving medications known to alter the hypothalamic-pituitary-adrenal axis were tested for PPID by evaluation of endogenous plasma ACTH concentration. Signalment, suspected cause, month of onset and duration of laminitis, Obel grade of lameness, pedal bone rotation, physical examination findings, results of endocrine function tests, treatment, outcome, and postmortem examination findings were recorded.

Results—Prevalence of PPID as defined by a single high plasma ACTH concentration was 70%. Median age of horses suspected of having PPID (n = 28) was 15.5 years, and median age of horses without PPID (12) was 14.5 years. Laminitis occurred most frequently in horses with and without suspected PPID during September and May, respectively. Chronic laminitis was significantly more common in horses suspected of having PPID. In horses suspected of having PPID, the most common physical examination findings included abnormal body fat distribution, bulging supraorbital fossae, and hirsutism. Five horses suspected of having PPID had no clinical abnormalities other than laminitis. Seventeen horses suspected of having PPID that were treated with pergolide survived, and 3 horses that were not treated survived.

Conclusions and Clinical Relevance—Evidence of PPID is common among horses with laminitis in a primary-care ambulatory setting. Horses with laminitis may have PPID without other clinical signs commonly associated with the disease. (J Am Vet Med Assoc 2004;224:1123–1127)

Full access
in Journal of the American Veterinary Medical Association


Objective—To measure plasma ACTH, D-melanocyte–stimulating hormone (D-MSH), and insulin concentrations during various photoperiods between February and October in horses and ponies with and without pituitary pars intermedia dysfunction (PPID).

Design—Cohort study.

Animals—13 clinically normal (control) ponies, 14 clinically normal (control) horses, 7 ponies with PPID, and 8 horses with PPID.

Procedures—Blood samples were collected from February through October during 8 photoperiods: 1, February 13 through March 2; 2, April 4 through 6; 3, June 19 through 22; 4, August 6 through 7; 5, August 14 through 17; 6, September 4 through 6; 7, September 26 through 28; and 8, October 16 through 18. Plasma ACTH, D-MSH, and insulin concentrations at each photoperiod were compared among groups.

Results—Log ACTH concentration was increased during photoperiod 4 through 8, compared with photoperiod 1 through 3, in all groups. In photoperiod 3 through 7, log ACTH concentrations were higher in horses and ponies with PPID, compared with values for control horses and ponies. D-Melanocyte–stimulating hormone (log and raw value) concentration was higher in photoperiod 2 through 8, compared with photoperiod 1, in control horses and ponies. In horses and ponies with PPID, log D-MSH concentration was higher in photoperiod 3 through 8, and D-MSH concentration was higher in photoperiod 4 through 8, compared with photoperiod 1. In control horses and ponies, plasma insulin concentration was lower in photoperiod 3 than in photoperiod 1.

Conclusions and Clinical Relevance—Plasma D-MSH and ACTH concentrations increased as daylight decreased from summer solstice (maximum daylight hours) to 12 hours of daylight.

Full access
in Journal of the American Veterinary Medical Association