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Abstract

Objective—To determine whether the method of lipopolysaccharide (LPS) administration (intermittent vs continuous) affects the magnitude and duration of the systemic inflammatory response in horses and whether prolonged (48 hours) endotoxemia induces laminitis.

Animals—12 healthy adult horses (10 mares and 2 geldings).

Procedures—Horses were randomly assigned to receive LPS (total dose, 80 μg; n = 4) or saline (0.9% NaCl) solution (80 mL/h; 4) via constant rate infusion or 8 bolus IV injections of LPS (10 μg, q 6 h;4) during a 48-hour period. Physical examinations were performed every 4 hours, inflammatory cytokine gene expression was determined for blood samples obtained every 8 hours, and IV glucose tolerance tests were performed.

Results—All LPS-treated horses had signs of depression and mild colic; those signs abated as the study progressed. Administration of LPS increased expression of interleukin-1β, interleukin-6, and interleukin-8, but results were not significantly different between LPS treatment groups. Cytokine expression was significantly higher on the first day versus the second day of LPS treatment. Interleukin-1β expression was positively correlated with rectal temperature and expression of other cytokines. Glucose and insulin dynamics for both LPS groups combined did not differ significantly from those of the saline solution group. Signs of laminitis were not detected in any of the horses.

Conclusions and Clinical Relevance—Horses developed LPS tolerance within approximately 24 hours after administration was started, and the method of LPS administration did not affect the magnitude or duration of systemic inflammation. Laminitis was not induced in horses.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To assess antiulcerogenic properties of 3 dietary oils.

Animals—8 healthy adult mares.

Procedure—A protocol to induce gastric ulcers was used and included 240 mL of water plus corn oil, refined rice bran oil, or crude rice bran oil administered each day for 6 weeks according to a 4 × 4 Latin square randomized crossover design with 5-week washout intervals. A 7-day alternating feed deprivation period was included between weeks 5 and 6. Omeprazole was administered daily for the last 14 days of each washout interval. Endoscopic examinations of the stomach were performed at 0, 5, and 6 weeks, and the number (0 to 4 scale) and severity (0 to 5 scale) of ulcers were scored. Gastric fluid was collected at 0 and 5 weeks.

Results—Median body weight significantly increased by 29 kg (range, 10 to 50 kg). Mean ± SE gastric fluid pH significantly decreased from 4.9 ± 0.4 to 3.1 ± 0.3 over 5 weeks, and total volatile fatty acid concentration significantly decreased over time. Mean ± SE severity of nonglandular ulcers significantly increased from 0.4 ± 0.1 to 1.2 ± 0.2 over 5 weeks. Nonglandular ulcers significantly increased in number (mean ± SE, 1.3 ± 0.2 to 3.0 ± 0.2) and severity (mean ± SE, 1.2 ± 0.2 to 2.6 ± 0.2) during the 7-day alternating feed deprivation period. No effects of treatment were detected.

Conclusions and Clinical Relevance—In this model dietary oils did not prevent gastric ulcers from forming in the nonglandular portion of the stomach of horses. (Am J Vet Res 2005;66:2006–2011)

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To assess relationships between horse owners (or lessees) and geriatric or nongeriatric horses and to investigate factors influencing veterinary care decision-making.

DESIGN Descriptive, cross-sectional, survey-based study.

SAMPLE 2,879 people who owned or leased ≥ 1 horse.

PROCEDURES Participants were recruited through social media and online horse forums to participate in an online survey about their horses, including measures of attachment, veterinary care decision-making, and experiences surrounding the death of a horse. Data were collected for primary horses (those respondents interacted with most) and secondary horses. Horses were further categorized as geriatric (≥ 20 years of age) and nongeriatric.

RESULTS Geriatric primary horses were considered companion animals, retired, or used as part of a business significantly more frequently, and described as competition horses significantly less frequently, than nongeriatric horses. Geriatric horses were owned or leased significantly longer than nongeriatric horses, but the degree of respondents' attachment did not differ for geriatric versus nongeriatric horses. When respondents reported the death of a horse in the previous year, euthanasia was associated with higher levels of bereavement than death by other means. Death of geriatric horses most commonly followed a chronic illness and was associated with significantly higher levels of bereavement than death of nongeriatric horses. Among factors influencing decisions regarding expensive or long-term medical care, the horse's ability to lead a comfortable life was ranked highest. Respondents with geriatric horses made numerous accommodations for their care.

CONCLUSIONS AND CLINICAL RELEVANCE Results provided important initial information about the relationships people have with geriatric horses. Understanding how individuals perceive their horses and how they make decisions regarding complex veterinary care is critical in informing effective client communication.

Restricted access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To compare blood lipid concentrations and lipoprotein patterns for captive and wild American black bears (Ursus americanus).

Animals—7 captive and 9 wild adult (≥ 4 years old) black bears.

Procedure—Blood was collected from 2 groups of captive black bears (groups A and B) and 1 group of wild black bears (group C). Blood triglyceride (TG) and cholesterol concentrations were compared among groups. Plasma lipoproteins were isolated by use of a self-generating gradient of iodixanol, and lipoprotein patterns were compared between groups A and B.

Results—Captive bears (mean ± SD, 187.8 ± 44.4 kg) weighed significantly more than wild bears (mean, 104.8 ± 41.4 kg), but mean body weight did not differ between groups A and B. Mean blood TG concentrations for groups B (216.8 ± 16.0 mg/dL) and C (190.7 ± 34.0 mg/dL) were significantly higher than that of group A (103.9 ± 25.3 mg/dL). Mean blood cholesterol concentration was also significantly higher for group B (227.8 ± 8.2 mg/dL) than for groups A (171.7 ± 35.5 mg/dL) or C (190.8 ± 26.8 mg/dL). Mean very-low-density lipoprotein TG and low-density lipoprotein cholesterol concentrations were 2- and 3-fold higher, respectively, for group B, compared with concentrations for group A.

Conclusions and Clinical Relevance—Blood lipid concentrations vary significantly among populations of black bears. Plasma lipoprotein patterns of captive bears differed significantly between colonies and may have reflected differences in diet or management practices.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To determine whether plasma ACTH concentrations vary following administration of a thyrotropin-releasing hormone (TRH) solution prepared for research purposes and stored at −20°C (rTRH) or prepared by a compounding pharmacy and stored at room temperature (approx 22°C; cTRH).

ANIMALS 34 adult horses.

PROCEDURES The study consisted of 2 experiments. In experiment 1, each horse underwent 2 TRH stimulation tests separated by 24 hours; 10 horses were administered cTRH for the first test and rTRH for the second test (group 1), 10 horses were administered rTRH for the first test and cTRH for the second test (group 2), and 10 horses were administered rTRH for both tests (group 3). Plasma ACTH concentrations were measured at 0 (baseline) and 30 minutes after TRH administration and the delta ACTH responses (change in ACTH concentration after TRH administration) were calculated. In experiment 2, the design was the same as that for experiment 1 except there were 14 days between tests, ACTH was measured at 0 and 10 minutes after TRH administration, and 11, 9, and 10 horses were assigned to groups 1, 2, and 3, respectively.

RESULTS Adverse effects associated with TRH administration included transient coughing and yawning. In experiment 1, the median delta ACTH response for the second test was significantly lower than that for the first test for all groups. In experiment 2, the median delta ACTH response did not differ significantly between the first and second tests for any group, ACTH concentrations after rTRH administration were positively correlated (r s = 0.95) with those after cTRH administration, and the mean ± SD bias in post-TRH ACTH concentration between rTRH and cTRH was 2.9 ± 12.4 pg/mL.

CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that the TRH stimulation test should not be repeated within 24 hours, and cTRH solution stored at room temperature could be used to effectively perform TRH stimulation testing in horses.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To test the hypothesis that inflammatory responses to endotoxemia differ between healthy horses and horses with equine metabolic syndrome (EMS).

Animals—6 healthy horses and 6 horses with EMS.

Procedures—Each horse randomly received an IV infusion of lipopolysaccharide (20 ng/kg [in 60 mL of sterile saline {0.9% NaCl} solution]) or saline solution, followed by the other treatment after a 7-day washout period. Baseline data were obtained 30 minutes before each infusion. After infusion, a physical examination was performed hourly for 9 hours and at 15 and 21 hours; a whole blood sample was collected at 30, 60, 90, 120, 180, and 240 minutes for assessment of inflammatory cytokine gene expression. Liver biopsy was performed between 240 and 360 minutes after infusion.

Results—Following lipopolysaccharide infusion in healthy horses and horses with EMS, mean rectal temperature, heart rate, and respiratory rate increased, compared with baseline findings, as did whole blood gene expression of interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor-α. The magnitude of blood cytokine responses did not differ between groups, but increased expression of IL-6, IL-8, IL-10, and tumor necrosis factor-α persisted for longer periods in EMS-affected horses. Lipopolysaccharide infusion increased liver tissue gene expressions of IL-6 in healthy horses and IL-8 in both healthy and EMS-affected horses, but these gene expressions did not differ between groups.

Conclusions and Clinical Relevance—Results supported the hypothesis that EMS affects horses’ inflammatory responses to endotoxin by prolonging cytokine expression in circulating leukocytes. These findings are relevant to the association between obesity and laminitis in horses with EMS.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To ascertain whether laminitis can be induced via administration of oligofructose (OF) at doses of 5.0 and 7.5 g/kg in horses and to assess glucose and insulin dynamics before and after treatment.

Animals—19 adult horses.

Procedures—Horses were fed OF (1.0 g/kg) mixed with oats for 6 days. Oligofructose at doses of 5.0 and 7.5 g/kg was then mixed with 4 L of water and administered (0 hours) to 8 (group A) and 4 (group B) horses, respectively, via nasogastric intubation; 8 horses received water alone. One horse in group A that did not develop laminitis was subsequently treated again and included in group B. Before and at intervals after treatment, resting plasma glucose and serum insulin concentrations were measured and frequently sampled IV glucose tolerance tests were performed. Area under the glucose curve (AUCg) and area under the insulin curve (AUCi) were calculated, and minimal model analyses were performed.

Results—3 of 8 horses in group A and all 4 horses in group B developed laminitis. Significant treatment-time effects were detected for resting plasma glucose concentrations and AUCg. Among horses in group A, mean AUCg values at 24 and 48 hours were 34% and 32% higher, respectively, than the mean value at 24 hours. Treatment groups did not differ significantly with respect to resting serum insulin concentration, AUCi, or minimal model analysis results.

Conclusions and Clinical Relevance—In horses, laminitis can be induced and glucose dynamics altered via nasogastric administration of 5.0 g of OF/kg. An alteration in insulin dynamics was not detected following treatment with OF.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of long-term oral levothyroxine sodium (L-T4) administration on serum thyroid hormone concentrations, thyroid gland function, clinicopathologic variables, and echocardiographic examination measurements in adult euthyroid horses.

Animals—6 healthy adult mares.

Procedures—Horses received L-T4 (48 mg/d) orally for 48 weeks. Every 4 weeks, physical examinations were performed; blood samples were collected for CBC, plasma biochemical analyses, and assessments of serum total triiodothyronine (tT3) and thyroxine (tT4) concentrations. Plasma creatine kinase MB activity and cardiac troponin I concentration were also measured. Echocardiographic examinations were performed before and at 16, 32, and 48 weeks during the treatment period.

Results—During the treatment period, mean body weight decreased significantly; heart rate varied significantly, but the pattern of variation was not consistent. Significant time effects were detected for certain clinicopathologic variables, but mean values remained within reference ranges. Cardiac troponin I was only detectable in 8 of 24 plasma samples (concentration range, 0.01 to 0.03 ng/mL). Serum creatine kinase MB activity did not change significantly over time. Compared with the pretreatment value, 5.4-, 4.0-, and 3.7-fold increases in mean serum tT4 concentrations were detected at 16, 32, and 48 weeks, respectively. Some cardiac measurements changed significantly over time, but mean values remained within published reference ranges. Mean fractional shortening was lower than the pretreatment mean value at 16 and 32 weeks.

Conclusions and Clinical Relevance—In horses, long-term oral administration of 48 mg of L-T4/d significantly increased serum tT4 concentrations and did not appear to adversely affect health.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of long-term oral administration of levothyroxine sodium (L-T4) on glucose dynamics in adult euthyroid horses.

Animals—6 healthy adult mares.

Procedures—Horses received L-T4 (48 mg/d) orally for 48 weeks. Frequently sampled IV glucose tolerance test procedures were performed on 3 occasions (24-hour intervals) before and at 16, 32, and 48 weeks during the treatment period. Data were assessed via minimal model analysis. The repeatability of measurements was evaluated.

Results—During treatment, body weight decreased significantly from the pretreatment value; mean ± SD weight was 49 ± 14 kg, 43 ± 7 kg, and 25 ± 18 kg less than the pretreatment value at weeks 16, 32, and 48, respectively. Compared with pretreatment findings, 1.8-, 2.4-, and 1.9-fold increases in mean insulin sensitivity (SI) were detected at weeks 16, 32, and 48, respectively; SI was negatively correlated with body weight (r = −0.42; P < 0.001). During treatment, glucose effectiveness increased and the acute insulin response to glucose decreased. Overall mean within-horse coefficients of variation were 5% and 29% for plasma glucose and serum insulin concentrations, respectively, and 33%, 26%, and 23% for SI, glucose effectiveness, and the acute insulin response to glucose, respectively.

Conclusions and Clinical Relevance—Long-term administration of L-T4 was associated with weight loss and increased SI in adult euthyroid horses, although other factors may have confounded results. Levothyroxine sodium may be useful for the treatment of obesity and insulin resistance in horses, but further studies are required.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To assess effects of withholding feed on thyrotropin-releasing hormone (TRH) stimulation test results used in diagnosis of pituitary pars intermedia dysfunction in horses and determine effects of combined testing on results of the TRH stimulation test and the oral sugar test (OST) used in diagnosis of equine metabolic syndrome.

ANIMALS 30 adult horses.

PROCEDURES All horses underwent TRH stimulation tests under fed and nonfed conditions, an OST alone, and an OST combined with TRH stimulation testing. For TRH stimulation tests, plasma ACTH concentrations were measured before (baseline) and 10 minutes after (poststimulation) IV TRH administration. For the OST, plasma glucose and insulin concentrations were measured before (baseline) and 60 and 90 minutes after oral corn syrup administration. For combined testing, the TRH stimulation test was initiated immediately after 60-minute posttreatment sample collection for the OST. Results were compared among methods by Wilcoxon matched-pairs, signed rank tests, paired t tests, and Bland-Altman analysis.

RESULTS Feeding conditions did not affect median ACTH concentrations when TRH stimulation tests were performed alone. Median baseline ACTH concentration did not differ between TRH stimulation tests performed alone (under fed or nonfed conditions) and those combined with OSTs. Median poststimulation ACTH concentration was significantly lower for combined tests than for solitary TRH stimulation tests. Mean 60-minute plasma glucose concentration was significantly lower for solitary OSTs than for combined tests, but this difference could not be attributed to TRH administration.

CONCLUSIONS AND CLINICAL RELEVANCE Combined testing in the manner described impacted ACTH concentrations during TRH stimulation tests and is not recommended at this time.

Full access
in American Journal of Veterinary Research