Effects of oral administration of levothyroxine sodium on serum concentrations of thyroid gland hormones and responses to injections of thyrotropin-releasing hormone in healthy adult mares

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 i.v., and serum concentrations of thyroid gland hormones were measured 2 and 4 hours after injection. Serum reverseT3 (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 toTRH injection in healthy euthyroid horses.     

Clinical and pathologic findings in donkeys with hypothermia: 10 cases (1988-1998)

OBJECTIVE: To describe clinical signs and clinicopathologic findings in donkeys with hypothermia. DESIGN: Retrospective study. ANIMALS: 10 hypothermic donkeys. PROCEDURE: Information on signalment, history, physical examination findings, results of diagnostic tests, treatments, and necropsy findings was extracted from medical records of all donkeys with hypothermia between 1988 and 1998 and compared with information from medical records of all normothermic donkeys and hypothermic horses admitted to the hospital during the same period. RESULTS: Donkeys were more likely to be hypothermic than horses. The mean age of hypothermic donkeys was 6 years (range, 7 months to 11 years), compared with 4.2 years (range, < 1 month to 15 years) for normothermic donkeys; this difference was not significant. Ten of 12 horses with hypothermia were neonates; there were no hypothermic neonatal donkeys. At admission, 7 of 8 hypothermic donkeys were in good body condition and all hypothermic donkeys were weak. Six hypothermic donkeys were able to maintain sternal recumbency, 1 remained in lateral recumbency, and 3 were able to stand. Of the 10 hypothermic donkeys, 2 survived, 1 died, and 7 were euthanatized. Histologically, the thyroid glands from 4 of 5 hypothermic donkeys appeared abnormal and were similar to those of foals with hypothyroidism. During the months that hypothermic donkeys were admitted, there was not a significant difference in environmental temperatures on days of admission between hypothermic and normothermic donkeys. CONCLUSIONS AND CLINICAL RELEVANCE: Hypothermia is a problem in donkeys during cold winter months, and may not be secondary to other disease or related to diet or management.     

Thyroid testing in Sloughis

Background: Thyroid hormone concentrations were found to be different in Greyhounds and Whippets compared with nonsight hound dogs.
Hypothesis: In Sloughis, thyroid hormone concentration is lower than in nonsight hounds and comparable to Greyhounds.
Animals: Fifty-one Sloughis with no evidence of disease and a mean age of 4 years (range, 1–12 years).
Methods: Thyroid profiles consisting of total thyroxine (tT4), free thyroxine (fT4), free thyroxine after equilibrium dialysis (fT4 after ED), canine thyroid stimulation hormone (cTSH), and thyroglobulin antibodies as well as CBC and serum biochemistry results of Sloughis were compared with those of normal dogs. In 8 Sloughis, TSH stimulation tests were performed.
Results: In Sloughis, tT4 concentrations and fT4 concentrations measured by chemiluminescence were lower than those of controls (1.13 ± 0.65 μg/dL compared with 2.9 ± 0.8 μg/dL, P < .0001 and 11 ± 4.3 pmol/L compared with 16.7 ± 5.2 pmol/L, P < .0001, respectively). Concentrations of fT4 after ED and TSH were increased in Sloughis, when compared with controls (41.3 ± 26.9 pmol/L compared with 20.98 ± 10.29 pmol/L, P < .0001 and 0.22 ± 0.15 pmol/L compared with 0.15 ± 0.13 pmol/L, P = .0138, respectively). T4 concentration after TSH stimulation increased from 1.5 μg/dL (range, 0.2–2.7 μg/dL) to 2.7 μg/dL (range, 1.2–4.7 μg/dL); the recommended post-TSH T4 concentration was achieved by only 3 of 8 Sloughis. Hemoconcentration was found in 84.3% and hypoglobulinemia in 80.3%.
Conclusions and Clinical Importance: When evaluating Sloughis for hypothyroidism, veterinarians should be aware that these dogs have different thyroid hormone concentrations than nonsight hound dogs.     

Short-term influence of prednisone and phenobarbital on thyroid function in euthyroid dogs.

The short-term effects of prednisone and phenobarbital on serum total thyroxine (tT4), free thyroxine (fT4), and thyroid stimulating hormone (TSH) were evaluated in euthyroid dogs. Twenty-six beagles were randomly divided into 3 groups receiving, respectively, a placebo, prednisone (1.2 to 2 mg/kg body weight, per os, every 12 hours for 3 weeks), or phenobarbital (1.8 to 3 mg/kg body weight for 1 week, then 2.7 to 4.5 mg/kg body weight, per os, every 12 hours for 2 weeks). Blood samples taken over a 6-week period were assayed for serum tT4, fT4, and TSH. Phenobarbital therapy in our study did not affect serum tT4, fT4, or TSH concentrations. Prednisone therapy, however, significantly decreased serum tT4 and fT4, but did not affect serum TSH concentrations.     

Endotoxn-induced nonthyroidal illness in dogs

OBJECTIVE: To determine the effects of endotoxin administration on thyroid function test results and serum tumor necrosis factor-alpha (TNF-alpha) activity in healthy dogs. ANIMALS: 6 healthy adult male dogs. PROCEDURES: Serum concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3'5'-triiodothyronine (rT3), free T4 (fT4), and endogenous canine thyroid stimulating hormone (TSH), and TNF-alpha activity were measured before (day-1; baseline), during (days 0 to 3), and after (days 4 to 24) IV administration of endotoxin every 12 hours for 84 hours. RESULTS: Compared with baseline values, serum T3 concentration decreased significantly, whereas rT3 concentration increased significantly 8 hours after initial endotoxin administration. Serum T4 concentration decreased significantly at 8 and 12 hours after initiating endotoxin administration. Serum T4 concentration returned to reference range limits, then decreased significantly on days 6 to 12 and 16 to 20. Serum fT4 concentration increased significantly at 12, 24, and 48 hours after cessation of endotoxin treatment, compared with baseline values. Serum rT3 concentration returned to reference range, then decreased significantly days 5 and 7 after stopping endotoxin treatment. Serum TNF-alpha activity was significantly increased only 4 hours after initial endotoxin treatment, compared with baseline activity. CONCLUSIONS AND CLINICAL RELEVANCE: Endotoxin administration modeled alterations in thyroid function test results found in dogs with spontaneous nonthyroidal illness syndrome. A decrease in serum T4 andT3 concentrations and increase in serum rT3 concentration indicate impaired secretion and metabolism of thyroid hormones. The persistent decrease in serum T4 concentration indicates that caution should be used in interpreting serum T4 concentrations after resolution of an illness in dogs.     

Assessment of serum thyroid hormone concentrations in lambs with selenium deficiency myopathy

OBJECTIVE: To assess changes in serum concentrations of thyroid hormones associated with selenium deficiency myopathy in lambs. ANIMALS: 35 lambs with selenium deficiency myopathy and 30 healthy lambs. PROCEDURES: Blood samples were collected via jugular venipuncture from lambs with selenium deficiency myopathy and healthy lambs. Activities of markers of selenium deficiency myopathy (erythrocyte glutathione peroxidase [GSH-Px] and plasma creatine kinase [CK]) and serum thyroid-stimulating hormone (TSH) and total thyroxine (tT(4)) and total triiodothyronine (tT(3)) concentrations were assessed; values in affected lambs were compared with those in healthy lambs. Correlations of erythrocyte GSH-Px and plasma CK activities with serum concentrations of TSH, tT(4), and tT(3) were investigated, and the tT(3):tT(4) concentration ratio was evaluated. RESULTS: Compared with findings in healthy lambs, erythrocyte GSH-Px activity, serum tT(3) concentration, and tT(3):tT(4) concentration ratio were significantly decreased and serum concentrations of tT(4) and TSH and the activity of plasma CK were significantly increased in affected lambs. Analysis revealed a significant negative correlation in the affected group between erythrocyte GSH-Px activity and each of the following: plasma CK activity (r = -0.443), serum TSH concentration (r = -0.599), serum tT(4) concentration (r = -0.577), and serum tT(3) concentration (r = -0.621). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that notable changes in circulating amounts of thyroid hormones develop in association with selenium deficiency in lambs. Such alterations in thyroid hormone metabolism may be involved in the high incidence of disorders, such as stillbirths and neonatal deaths, in selenium-deficient flocks.     

Pharmacokinetics of sulfamethoxazole and trimethoprim in donkeys, mules, and horses

OBJECTIVE: To compare serum disposition of sulfamethoxazole and trimethoprim after IV administration to donkeys, mules, and horses. ANIMALS: 5 donkeys, 5 mules, and 3 horses. PROCEDURE: Blood samples were collected before (time 0) and 5, 15, 30, and 45 minutes and 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 8, 10, and 24 hours after IV administration of sulfamethoxazole (12.5 mg/kg) and trimethoprim (2.5 mg/kg). Serum was analyzed in triplicate with high-performance liquid chromatography for determination of sulfamethoxazole and trimethoprim concentrations. Serum concentration-time curve for each animal was analyzed separately to estimate noncompartmental pharmacokinetic variables. RESULTS: Clearance of trimethoprim and sulfamethoxazole in donkeys was significantly faster than in mules or horses. In donkeys, mean residence time (MRT) of sulfamethoxazole (2.5 hours) was less than half the MRT in mules (6.2 hours); MRT of trimethoprim in donkeys (0.8 hours) was half that in horses (1.5 hours). Volume of distribution at steady state (Vdss) for sulfamethoxazole did not differ, but Vdss of trimethoprim was significantly greater in horses than mules or donkeys. Area under the curve for sulfamethoxazole and trimethoprim was higher in mules than in horses or donkeys. CONCLUSIONS AND CLINICAL RELEVANCE: Dosing intervals for IV administration of trimethoprim-sulfamethoxazole in horses may not be appropriate for use in donkeys or mules. Donkeys eliminate the drugs rapidly, compared with horses. Ratios of trimethoprim and sulfamethoxazole optimum for antibacterial activity are maintained for only a short duration in horses, donkeys, and mules.     

Cardiovascular changes in horses with atrial fibrillation and high thyroid hormone concentration: a case–control study

IntroductionHyperthyroidism is a predisposing factor for atrial fibrillation (AF) in humans. The relationship between high thyroid hormone (TH) and AF in horses has not been evaluated.ObjectivesThe aim of this study is to identify whether (1) high TH concentrations were present in horses with AF, (2) other cardiovascular effects were observed in horses with high TH and AF, and (3) TH status affected recurrence rate.AnimalsTwenty-three horses presented with naturally occurring AF.MethodsProspective case–control clinical study. Thyroid hormone concentration was measured in horses presenting with AF. Heart rate, electrocardiogram, blood pressure, and an echocardiogram were recorded as part of their clinical workup. Recurrence rate was determined by owner/veterinarian follow-up.ResultsHigh TH concentration was found in 60% of horses with AF. Horses in the high TH group had a higher heart rate (P=0.001), systolic blood pressure (P=0.019), left ventricular free wall thickness (P=0.026), relative wall thickness (P=0.041) and were more likely to have periods of AF with a rapid ventricular response rate (P=0.022). All horses were successfully converted to normal sinus rhythm. The likelihood of recurrence was not different between groups.ConclusionElevated TH concentration can be found in horses with AF. Other cardiovascular effects of high TH concentrations in other species were also present in horses with AF and elevated TH concentrations. This study recommends measuring TH concentrations in horses presenting for AF with a history of thyroid or iodine supplementation. This study also cautions against TH or iodine supplementation in healthy performance horses.     

Measurement of free thyroxine concentration in horses by equilibrium dialysis

The purpose of the study reported here was to validate measurement of free thyroxine (fT4) concentration in equine serum by equilibrium dialysis (fT4D), and to compare values with fT4 concentration measured directly and with total T4 (TT4) concentration. The fT4D, fT4, and TT4 concentrations were measured over a range of values in euthyroid horses and horses made hypothyroid by administration of propylthiouracil (PTU). Concentrations of fT4D (<1.8-83 pmol/L) were consistently higher than those of fT4 (<1-40 pmol/L). There was a significant (P < .001) regression of fT4D on fT4 in 503 samples from normal horses (y = 2.086x - 0.430). In baseline samples from 71 healthy euthyroid horses, fT4 concentration ranged from 6-21 pmol/L (median, 11 pmol/L; 95% confidence interval [CI]10.5-11.8 pmol/L), and fT4D concentration ranged from 7-47 pmol/L (median, 22 pmol/L; 95% CI 20.9-25.1 pmol/L). Free T4D, fT4, and TT4 concentrations were also measured in 34 ill horses. Horses consuming PTU and ill horses had significantly (P < .05) lower serum concentration of TT4, fT4, and fT4D than did clinically normal, healthy horses. If serum samples from ill horses were further subdivided into samples from horses that lived and samples from horses that died, fT4D concentration was not significantly different in ill horses that lived, compared with that in healthy horses, whereas fT4 concentration was still significantly decreased in ill horses that died (P < 0.001). We conclude that measurement of fT4 concentration by equilibrium dialysis is a valid technique in the horse, and its use may provide improved ability to distinguish nonthyroidal illness syndrome from hypothyroidism in that species.     

Effects of propylthiouracil and bromocryptine on serum concentrations of thyrotrophin and thyroid hormones in normal female horses

REASONS FOR PERFORMING STUDY: There exists a need for better diagnostic tests to characterise thyroid disease in horses. Currently available diagnostic tests fail to differentiate between thyroid gland disorders and thyroid abnormalities resulting from pituitary or hypothalamic problems. OBJECTIVES: To evaluate the effects of treatment with propylthiouracil (PTU) and bromocryptine (BROM) on serum concentrations of triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3) and equine thyroid-stimulating hormone (e-TSH, thyrotrophin) in mature horses. METHODS: Healthy mature horses were treated using either PTU or BROM for 28 days. The effect of treatment on the thyroid axis was assessed by measuring T3, T4, rT3 and e-TSH before and at +14 and +28 days. The effect of PTU and BROM on the response of T3, T4, rT3 and e-TSH to thyrotrophin-release hormone (TRH) administration was also assessed before and at +14 and +28 days of treatment. RESULTS: Treatment with PTU led to a significant reduction in serum concentrations of T3, T4 and rT3 on Day 28 and increase of e-TSH on Day 28 (P < 0.05). Treatment with BROM did not cause any measurable effect on serum concentrations of T3, T4, rT3 or e-TSH. The percentage increment by which serum concentration of T4, T3 and e-TSH increased following stimulation with TRH was decreased by treatment with PTU for 28 days (P < 0.05) but were not affected by treatment with BROM for 28 days. CONCLUSIONS: These results suggest that 1) treatment with PTU may be used in horses as a model of primary hypothyroidism; 2) the use of BROM as a model of secondary hypothyroidism in horses is not supported; and 3) e-TSH assay deserves further investigation for the clinical diagnosis of thyroid axis dysfunction in horses. POTENTIAL RELEVANCE: Propylthiouracil effectively causes primary hypothyroidism. There is substantial variability between horses with respect to their sensitivity to this substance when administered orally. Further studies pertaining to the characterisation of equine thyroid disorders are warranted and the use of both PTU for the experimental induction of primary hypothyroidism and e-TSH for the diagnostic characterisation of thyroid disorders in horses should be considered.     

Effects of long-term oral administration of levothyroxine sodium on serum thyroid hormone concentrations, clinicopathologic variables, and echocardiographic measurements in healthy adult horses

OBJECTIVE: To determine the effects of long-term oral levothyroxine sodium (L-T(4)) 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-T(4) (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 (tT(3)) and thyroxine (tT(4)) 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 tT(4) 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-T(4)/d significantly increased serum tT(4) concentrations and did not appear to adversely affect health.     

Evaluation of the effects of clomipramine on canine thyroid function tests

To evaluate the effect of long-term clomipramine administration on the hypothalamic-pituitary-thyroid axis in healthy dogs, 14 healthy adult dogs were enrolled in a prospective study. Clomipramine (3 mg/kg PO q12h) was administered to all dogs beginning on day 0, and continued for 112 days. Serum total thyroxine (T4), free thyroxine (fT4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3; rT3), and thyroid-stimulating hormone (TSH) were measured on days 0, 7, 28, 42, 56, and 112. Thyrotropin-releasing hormone (TRH) response tests were performed concurrently. Significant decreases were noted in serum T4, f4, and rT3 concentrations beginning on day 28 through the end of the study period. The lowest mean (+/-SEM) concentrations of T4 (26 +/- 1.2 to 17 +/- 0.5 nmol/L) and rT3 (1.21 +/- 0.13 to 0.83 +/- 0.08 nmol/L) occurred at day 112, whereas the lowest mean fT4 (29 +/- 2.4 to 18 +/- 1.7 pmol/L) was found on day 56 of clomipramine treatment. The effect of treatment over time on serum T3 concentration also was significant, but the deviation in T3 from baseline was variable. No significant effect of clomipramine treatment was noted on either pre- or post-TRH TSH concentrations. The 35 and 38% decreases in serum T4 and fT4 concentrations, respectively, during clomipramine administration may lead to a misdiagnosis of hypothyroidism. Although no evidence of hypothyroidism was noted in this study population, subclinical hypothyroidism may have occurred. A longer duration of treatment might further suppress thyroid function, and concurrent illness or other drug administration might exacerbate clomipramine's effects.     

Changes in thyroxine, 3,3',5-triiodothyronine and 3,3'5'-triiodothyronine content in the thyroid gland and in serum to thyroid tissue iodothyronine ratios during ontogenesis in the fetal pig

The concentrations of thyroxine (T4), 3,3',5-triiodothyronine (T3) and 3,3',5'-triiodothyronine (reverse T3; rT3) in thyroid gland tissue and serum of the fetal pig (n = 68) from day 39 to 113 of gestation were measured. Tracer quantities of iodothyronines, displaying the onset of thyroid hormone activity, were found in the thyroid tissue on day 39, i.e. before the appearance of a measurable quantity of iodothyronines in the serum. The T4 and T3 thyroidal content showed the first rise between days 56 and 76. Then, T3 was increasing sharply from day 92 till birth, while T4 content was decreasing from about day 76 to a low value between day 92 and 105, and then showing an increase shortly before birth. The rT3 content was the highest on day 39 and then it was steadily decreasing to reach a nadir on about day 76. Measurable amounts of thyroid hormones (TH) in the serum were observed not earlier than on day 46 of gestation. Near birth, the tissues of the pig fetus are in a milieu characterised by the highest blood TH concentrations. The serum to thyroid concentration ratio for rT3 and T4 was generally below 1.0 until the last trimester of gestation, when it was over 5.0 for rT3 and over 4.0 for T4. By contrast, the T3 serum to thyroid ratio was below 0.5 throughout the gestation. The results show that the fetal pig thyroid displays a low rT3 and T4 content, but the marked T3 elevation observed near term supports the view that a high production and secretion of T3 near term may be a critical factor for normal postnatal adaptation to extrauterine cooling in the pig.     

Comparison of serum-free thyroxine concentrations determined by standard equilibrium dialysis, modified equilibrium dialysis, and 5 radioimmunoassays in dogs

Measurement of serum-free thyroxine (fT4) concentration provides a more accurate assessment of thyroid gland function than serum thyroxine (T4) or 3,5,3'-triiodothyronine (T3). Techniques for measuring serum fT4 concentration include standard equilibrium dialysis (SED), radioimmunoassay (RIA), and a combination of both (modified equilibrium dialysis [MED]). This study compared results of serum fT4 measurements by means of SED, MED, and 5 RIAs in 30 healthy dogs, 10 dogs with hypothyroidism, and 31 euthyroid dogs with concurrent illness for which hypothyroidism was a diagnostic consideration. Serum fT4 concentrations were comparable when determined by the SED and MED techniques, and mean serum fT4 concentrations were significantly (P < .01) lower in dogs with hypothyroidism than in healthy dogs and euthyroid dogs with concurrent illness. Significant (P < .05) differences in fT4 concentrations were identified among the 5 RIAs and among the RIAs and MED and SED. Serum fT4 concentrations were consistently lower when fT4 was determined by the RIAs, compared with either equilibrium dialysis technique. Serum fT4 concentrations were significantly lower (P < .01) in dogs with hypothyroidism than in healthy dogs for all RIAs; were significantly lower (P < .05) in dogs with hypothyroidism than in euthyroid dogs with concurrent illness for 4 RIAs; and were significantly lower (P < .01) in euthyroid dogs with concurrent illness than in healthy dogs for 4 RIAs. RIAs had the highest number of low serum fT4 concentrations in euthyroid dogs with concurrent illness. This study documented differences in test results among fT4 assays, emphasizing the importance of maintaining consistency in the assay used to measure serum fT4 concentrations in the clinical or research setting.     

Comparison of colloid,thyroid follicular epithelium,and thyroid hormone concentrations in healthy and severely sick dogs

OBJECTIVES: To compare serum concentrations of total thyroxine (TT4), free thyroxine (fT4), and thyroid-stimulating hormone (TSH), as well as measures of thyroid follicular colloid and epithelium, between groups of healthy dogs and severely sick dogs. DESIGN: Cross-sectional study. ANIMALS: 61 healthy dogs and 66 severely sick dogs. PROCEDURE: Serum samples were obtained before euthanasia, and both thyroid lobes were removed immediately after euthanasia. Morphometric analyses were performed on each lobe, and serum TT4, fT4, and TSH concentrations were measured. RESULTS: In the sick group, serum TT4 and fT4 concentrations were less than reference range values in 39 (59%) and 21 (32%) dogs, respectively; only 5 (8%) dogs had high TSH concentrations. Mean serum TT4 and fT4 concentrations were significantly lower in the sick group, compared with the healthy group. In the healthy group, a significant negative correlation was found between volume percentage of colloid and TT4 or fT4 concentrations, and a significant positive correlation was found between volume percentage of follicular epithelium and TT4 or fT4 concentrations. A significant negative correlation was observed between volume percentages of colloid and follicular epithelium in both groups. CONCLUSIONS AND CLINICAL RELEVANCE: TT4 and fT4 concentrations are frequently less than reference range values in severely sick dogs. Therefore, thyroid status should not be evaluated during severe illness. The absence of any significant differences in mean volume percentages of follicular epithelium between healthy and severely sick dogs suggests that these 2 groups had similar potential for synthesizing and secreting thyroid hormones.     

Seroepidemiological survey of Rhodococcus equi infection in asymptomatic horses and donkeys from southeast Turkey

In order to assess the level of Rhodococcus equi infection in southeast Turkey, 679 sera from healthy foals and adult horses and 78 sera from donkeys were tested by indirect ELISA using a R. equi reference strain (ATCC 33701) as antigen. Eighty (11.7%) sera from horses and 9 (11.5%) sera from donkeys with titres >0.85 were positive. The prevalence of seropositive horses in Sanliurfa Province was higher than in Diyarbakir Province; 56 (13.9%) horses in Sanliurfa Province and 24 (8.7%) horses in Diyarbakir Province were defined as seropositive. In Sanliurfa Province 14.5% of female (n=343) and 10.1% of male (n = 59) horses tested were defined as seropositive, while in Diyarbakir Province more males (11.4%, n=114) were seropositive than females (6.7%, n=163). Horses 1 to 5 years of age were found to have the highest seropositivity rate in both provinces. A total of 78 sera from donkeys were investigated in Sanliurfa Province, of which 9 (11.5%) were positive by ELISA. Among the 9 positive sera, 6 (12.8%) were from donkeys 1-5 years old and 3 (13.6%) were from donkeys >5 years of age. No positive sera were found in donkeys less than 1 year old. Five (12.5%) sera of females and 4 (10.5%) sera of males tested were positive. These results indicate the existence of R. equi in the horse populations in Sanliurfa and Diyarbakir Provinces. Similar infection rates were found for donkeys in Sanliurfa. This suggests the importance of serological surveys to diagnose R. equi infection in the region and to prevent the zoonotic risk.     

Alterations in thyroid hormone concentrations in healthy sled dogs before and after athletic conditioning

OBJECTIVE: To determine effects of athletic conditioning on thyroid hormone concentrations in a population of healthy sled dogs. ANIMALS: 19 healthy adult sled dogs. PROCEDURE: Serum concentrations of thyroxine (T4), triiodothyronine (T3), thyroid-stimulating hormone (TSH), free T4 (fT4), free T3 (fT3), and autoantibodies directed against T3, T4, and thyroglobulin were measured in sled dogs that were not in training (ie, nonracing season) and again after dogs had been training at maximum athletic potential for 4 months. RESULTS: Analysis revealed significant decreases in T4 and fT4 concentrations and a significant increase in TSH concentration for dogs in the peak training state, compared with concentrations for dogs in the untrained state. Serum concentrations of T4 and fT4 were less than established reference ranges during the peak training state for 11 of 19 and 8 of 19 dogs, respectively; fT4 concentration was greater than the established reference range in 9 of 19 dogs in the untrained state. CONCLUSIONS AND CLINICAL RELEVANCE: Decreased total T4 and fT4 concentrations and increased serum concentrations of TSH were consistently measured during the peak training state in healthy sled dogs, compared with concentrations determined during the untrained state. Although thyroid hormone concentrations remained within the established reference ranges in many of the dogs, values that were outside the reference range in some dogs could potentially lead to an incorrect assessment of thyroid status. Endurance training has a profound impact on the thyroid hormone concentrations of competitive sled dogs.     

Coagulation profiles of healthy Andalusian donkeys are different than those of healthy horses

Background: Coagulation disorders are frequently diagnosed, especially in hospitalized equidae, and result in increased morbidity and mortality. However, hemostatic reference intervals have not been established for donkeys yet. Objectives: To determine whether the most common coagulation parameters used in equine practice are different between healthy donkeys and horses. Animals: Thirty‐eight healthy donkeys and 29 healthy horses. Methods: Blood samples were collected to assess both coagulation and fibrinolytic systems by determination of platelet count, fibrinogen concentration, clotting times (prothrombin time [PT] and activated partial thromboplastin time [aPTT]), fibrin degradation products (FDP) and D‐Dimer concentrations. Results: PT and aPTT in donkeys were significantly (P < .05) shorter than those of horses. In contrast, FDP and D‐Dimer concentrations were significantly (P < .05) higher in donkeys than in horses. Conclusions and Clinical Importance: The coagulation parameters most commonly determined in equine practice are different in donkeys compared with horses. Thus, the use of normal reference ranges reported previously for healthy horses in donkeys might lead to a misdiagnosis of coagulopathy in healthy donkeys, and unnecessary treatments in sick donkeys. This is the first report of normal coagulation profile results in donkeys, and further studies are warranted to elucidate the physiological mechanisms of the differences observed between donkeys and horses.     

Comparative endocrinological responses to short transportation of Equidae (Equus asinus and Equus caballus)

In order to evaluate the effects of short transportation on β‐endorphin, adrenocorticotropic hormone (ACTH) and cortisol changes, 12 healthy stallions of Equidae (Equus asinus and Equus caballus) were studied before and after transportation of 50 km. Blood samples were collected 1 week before transportation in basal conditions, immediately before loading and after transportation and unloading, on their arrival at the breeding station. Compared to basal and before values, donkeys showed an increase in circulating ACTH (P < 0.001) and cortisol (P < 0.0005) levels after transportation and higher ACTH (P < 0.01) levels than horses after transportation. A positive and significant correlation (r = 0.885; P < 0.01) between ACTH and cortisol levels after transportation was found. No significant differences were observed for β‐endorphin levels. Compared to basal and before values, horses showed higher cortisol (P < 0.005) levels after transportation and no significant differences were observed for ACTH and β‐endorphin levels in donkeys. Horses facing forward (direction of travel) showed higher (P < 0.01) β‐endorphin levels after transportation than donkeys; horses facing backward (the opposite direction of travel) showed lower (P < 0.05) ACTH levels after transportation. The results indicate that short transportation induces a preferential activation of the hypothalamus‐pituitary‐axis (HPA), with significant release of ACTH and cortisol in donkeys and only of cortisol in horses, suggesting that transportation for donkeys may be more stressful than horses.     

Evaluation of microchip migration in horses, donkeys, and mules

OBJECTIVE: To determine whether microchips used for identification migrate after implantation in horses, donkeys, and mules. DESIGN: Prospective study. ANIMALS: 53 horses, donkeys, and mules. PROCEDURE: Twenty horses that had had microchips implanted in the nuchal ligament at a veterinary teaching hospital from 1996 through early 2000 were included (group 1), and the poll-to-withers distance and location of the microchip were determined, measured, and recorded. Additionally, the poll-to-withers distance was measured in 16 horses, 12 donkeys, and 5 mules (group 2), and microchips were implanted in the nuchal ligament on the left side of the neck. Forty-two to 67 days after implantation, the location of the microchip was determined, measured, and recorded. RESULTS: Microchips implanted in the nuchal ligament < or = 4 years previously did not migrate. All microchips were detected with a multimode identification tag reader from the left side of the neck in the midcervical region, and microchips were located at the midpoint between the poll and withers for all 53 horses, donkeys, and mules. CONCLUSIONS AND CLINICAL RELEVANCE: Microchips implanted in the nuchal ligament < or = 4 years earlier did not migrate in horses. Microchips may be useful for identification in horses.