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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 compare obese horses with insulin resistance (IR) with nonobese horses and determine whether blood resting glucose, insulin, leptin, and lipid concentrations differed between groups and were correlated with combined glucose-insulin test (CGIT) results.

Animals—7 obese adult horses with IR (OB-IR group) and 5 nonobese mares.

Procedures—Physical measurements were taken, and blood samples were collected after horses had acclimated to the hospital for 3 days. Response to insulin was assessed by use of the CGIT, and maintenance of plasma glucose concentrations greater than the preinjection value for ≥ 45 minutes was used to define IR. Area under the curve values for glucose (AUCg) and insulin (AUCi) concentrations were calculated.

Results—Morgan, Paso Fino, Quarter Horse, and Tennessee Walking Horse breeds were represented in the OB-IR group. Mean neck circumference and BCS differed significantly between groups and were positively correlated with AUC values. Resting insulin and leptin concentrations were 6 and 14 times as high, respectively, in the OB-IR group, compared with the nonobese group, and were significantly correlated with AUCg and AUCi. Plasma nonesterified fatty acid, very low-density lipoprotein, and high-density lipoprotein-cholesterol (HDL-C) concentrations were significantly higher (86%, 104%, and 29%, respectively) in OB-IR horses, and HDL-C concentrations were positively correlated with AUC values.

Conclusions and Clinical Relevance—Measurements of neck circumference and resting insulin and leptin concentrations can be used to screen obese horses for IR. Dyslipidemia is associated with IR in obese horses.

Restricted access
in Journal of the American Veterinary Medical Association

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 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 evaluate the effects of endotoxin administered IV on glucose and insulin dynamics in horses.

Animals—16 healthy adult mares.

Procedures—Each week of a 2-week randomized crossover study, each horse received an IV injection (duration, 30 minutes) of Escherichia coli O55:B5 lipopolysaccharide (LPS) in 60 mL of sterile saline (0.9% NaCl) solution (20 ng/kg) or sterile saline solution alone (control treatment). Frequently sampled IV glucose tolerance test procedures were performed at 24 hours before (baseline) and 24 and 48 hours after injection; glucose and insulin dynamics were assessed via minimal model analysis.

Results—13 of 16 horses had a clinical response to LPS, which was characterized by mild colic and leukopenia. Before treatment, mean ± SD insulin sensitivity was 2.9 ± 1.9 × 10−4 L·min−1·mU−1; this significantly decreased to 0.9 ± 0.9 × 10−4 L·min−1·mU−1 24 hours after treatment (69% reduction) and was 1.5 ± 0.9 × 10−4 L·min−1·mU−1 48 hours after treatment. At baseline, mean ± SD acute insulin response to glucose was 520 ± 196 mU·min·L−1; this significantly increased to 938 ± 620 mU·min·L−1 (80% increase) and 755 ± 400 mU·min·L−1 (45% increase) at 24 and 48 hours after LPS treatment, respectively.

Conclusions and Clinical Relevance—Compared with baseline values, insulin sensitivity was decreased for 24 hours after IV injection of LPS, and affected horses had a compensatory pancreatic response. These disturbances in glucose and insulin dynamics may contribute to development of laminitis in horses.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To compare the effects of hydrochloric acid (HCl) and various concentrations of volatile fatty acids (VFAs) on tissue bioelectric properties of equine stomach nonglandular (NG) mucosa.

Sample Population—Gastric tissues obtained from 48 adult horses.

Procedures—NG gastric mucosa was studied by use of Ussing chambers. Short-circuit current (Isc) and potential difference (PD) were measured and electrical resistance (R) and conductance calculated for tissues after addition of HCl and VFAs (5, 10, 20, and 40mM) in normal Ringer's solution (NRS).

Results—Mucosa exposed to HCl in NRS (pH of 1.5 and, to a lesser extent, 4.0) had a significant decrease in Isc, PD, and R, whereas tissues exposed to acetic acid at a pH of < 4.0, propionic and butyric acids at a pH of ≤ 4.0, and valeric acid at a pH of ≤ 7.0 induced a concentration-dependent effect on reduction in these same values. Values for Isc returned to baseline (recovery of sodium transport) after addition of calcium carbonate in tissues exposed to all concentrations of VFAs except the higher concentrations of valeric acid at a pH of ≤ 4.0. Histologic examination revealed cell swelling in the mucosal layers below and adjacent to the stratum corneum in tissues exposed to HCl and VFAs at a pH of ≤ 4.0.

Conclusions and Clinical Relevance—The VFAs, especially acetic acid, in the presence of HCl at a pH of ≤ 4.0 appear to be important in the pathogenesis of NG mucosal ulcers in horses.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether administration of isoflupredone acetate (ISO) to healthy cows increases the frequency of severe hypokalemia and whether dexamethasone (DEX) has detectable mineralocorticoid properties.

Animals—33 cows at 20 to 25 days of lactation.

Procedures—Cows were randomly allocated to 5 treatment groups and received 2 IM injections (on days 0 and 2) of sterile saline (0.9% NaCl) solution (10 mL each), an injection of ISO (20 mg) or DEX (20 mg) followed by 10 mL of saline solution, or 2 injections of ISO or DEX. Milk production was measured, physical examinations were performed, and blood and urine samples were collected daily on days 0 through 7.

Results—Physical examination parameters did not differ among groups; however, 1 cow developed atrial fibrillation on day 4. Both corticosteroids significantly increased plasma glucose concentrations, and ISO significantly decreased plasma potassium concentrations and increased total carbon dioxide concentrations with time. One dose of ISO decreased mean plasma potassium concentration by 25% on day 2, compared with day 0, and severe hypokalemia (serum potassium concentration < 2.3 mEq/L) developed in 1 of 6 cows. Mean plasma potassium concentration was 46% lower on day 3 than on day 0 in cows receiving 2 doses of ISO, and 5 of 7 cows became severely hypokalemic. Mean urinary fractional excretion of potassium significantly increased from that on day 0 in cows receiving 2 doses of ISO.

Conclusions and Clinical Relevance—Both corticosteroids had glucocorticoid activity; however, only ISO had mineralocorticoid activity. Compared with saline solution, administration of 2 doses of ISO significantly increased the frequency of severe hypokalemia.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of levothyroxine sodium (L-T4) on serum concentrations of thyroid gland hormones and responses to injections of thyrotropin-releasing hormone (TRH) in euthyroid horses.

Animals—12 healthy adult mares.

Procedure—8 horses received an incrementally increasing dosage of L-T4 (24, 48, 72, or 96 mg of L-T4/d) for weeks 1 to 8. Each dose was provided for 2 weeks. Four additional horses remained untreated. Serum concentrations of total triiodothyronine (tT3), total thyroxine (tT4), free T3 (fT3), free T4 (fT4), and thyroid- stimulating hormone (TSH) were measured in samples obtained at weeks 0, 2, 4, 6, and 8; 1.2 mg of TRH was then administered IV, and serum concentrations of thyroid gland hormones were measured 2 and 4 hours after injection. Serum reverse T3 (rT3) concentration was also measured in the samples collected at weeks 0 and 8.

Results—Treated horses lost a significant amount of weight (median, 19 kg). Significant treatment-by-time effects were detected for serum tT3, tT4, fT3, fT4, and TSH concentrations, and serum tT4 concentrations were positively correlated ( r, 0.95) with time (and therefore dosage) in treated horses. Mean ± SD serum rT3 concentration significantly increased in treated horses (3.06 ± 0.51 nmol/L for week 8 vs 0.74 ± 0.22 nmol/L for week 0). Serum tT3, tT4, fT3, and TSH concentrations in response to TRH injections differed significantly between treated and untreated horses.

Conclusions and Clinical Relevance—Administration of levothyroxine sodium increased serum tT4 concentrations and blunted responses to TRH injection in healthy euthyroid horses. (Am J Vet Res 2005;66:1025–1031)

Full access
in American Journal of Veterinary Research