Babetta A. Breuhaus

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 Trimethoprim‐Sulfadiazine on Thyroid Function of Horses

Trimethoprim-sulfadiazine was administered to horses in a randomized, placebo controlled study to determine the effects of potentiated sulfonamides on thyroid function in normal horses. The treatment group included eight horses that received trimethoprim-sulfadiazine mixed with molasses orally at 30 mg/kg once daily for eight weeks. The control group included 8 horses that received an oral placebo (flour mixed with molasses) once daily for the same period. Thyroid function was evaluated prior to initiation of treatment and after 8 weeks of treatment. Serum concentrations of total and free triiodothyronine (T3), total and free thyroxine (T4), and thyroid stimulating hormone (TSH) were determined at rest and after a thyrotropin-releasing hormone (TRH) stimulation test. There was no detectable difference between treatment and control groups.

Thyroid Function in Anhidrotic Horses

BACKGROUND This study was performed to determine whether anhidrotic horses have altered thyroid function compared with horses that sweat normally. HYPOTHESIS Anhidrotic horses have normal thyroid function. ANIMALS Ten client-owned horses with clinical signs of anhidrosis were paired with 10 horses living in the same environment that had normal sweat production. METHODS Horses were diagnosed as having normal sweat production or being anhidrotic based on responses to intradermal injections of terbutaline and physiologic responses to lunging exercise. Control horses were selected from the same environment and matched as closely as possible to anhidrotic horses in terms of age, sex, breed, and athletic condition. Thyrotropin-releasing hormone (TRH) stimulation tests were performed in both horses at the same time, once in the summer or fall, and once again in winter. RESULTS Anhidrotic horses produced less sweat in response to intradermal injections of terbutaline and exercise than did control horses. They also had greater increases in body temperature and respiratory rate in response to exercise. Resting concentrations of thyroid hormones and thyroid-stimulating hormone (TSH) were not different between anhidrotic and control horses. Thyroid hormone responses to TRH also were not different between the 2 groups of horses. However, anhidrotic horses had a significantly different TSH response to TRH compared with control horses, particularly in the winter. CONCLUSIONS AND CLINICAL IMPORTANCE The biologic relevance of the altered TSH response to TRH in anhidrotic horses is uncertain, considering that TSH concentrations remained within previously reported normal ranges and thyroid hormone responses were not different between anhidrotic and control horses.

Effects of quinapril on angiotensin converting enzyme and plasma renin activity as well as pharmacokinetic parameters of quinapril and its active metabolite, quinaprilat, after intravenous and oral administration to mature horses.

REASONS FOR PERFORMING STUDY Angiotensin converting enzyme (ACE) inhibitors improve survival and quality of life in human patients and small animals with cardiovascular and renal disease. There is limited information regarding their effects in horses. OBJECTIVES The purpose of this study was to determine the pharmacokinetics of quinapril and its effects on ACE and renin in horses. STUDY DESIGN Experimental study using healthy mature horses. METHODS Six healthy horses were administered quinapril at 120 mg i.v., 120 mg per os and 240 mg per os in a 3-way crossover design. Blood was collected for measurement of quinapril and quinaprilat concentrations using ultra-high pressure liquid chromatography with mass spectrometry. Angiotensin converting enzyme activity and renin activity were measured using a radioenzymatic assay. Noncompartmental pharmacokinetic modelling and statistical analyses were performed. RESULTS No adverse effects were observed during the study period. Intravenous and oral administration significantly inhibited ACE activity. Renin concentrations increased in all groups, but this increase was not statistically significant. Following i.v. administration of quinapril, mean terminal half-life was 0.694 h and 1.734 h for quinapril and quinaprilat, respectively. The mean volume of distribution and clearance for quinapril were 0.242 l/kg bwt and 11.93 ml/kg bwt/min, respectively. Maximum concentration for quinaprilat was 145 ng/ml at 0.167 h. Bioavailability of quinapril following oral administration was <5%. Quinaprilat was detected in all horses following oral administration of quinapril; however, it was below the limit of quantification of the assay (2.5 ng/ml) for most horses in the 120 mg dosing group. CONCLUSIONS These results suggest that, despite low plasma concentrations, quinapril has sufficient oral absorption to produce inhibition of ACE in healthy horses. Controlled studies in clinically affected horses are indicated. Quinapril provides a potential treatment alternative for horses with cardiovascular and renal disease.

Nonthyroidal Illness Syndrome in Adult Horses

Background This study was performed to determine whether sick horses have thyroid hormone (TH) alterations similar to those observed in nonthyroidal illness syndrome in other species. Hypothesis Horses suffering from systemic diseases have decreased THs and inappropriately low thyroid‐stimulating hormone (TSH). Animals Seventy‐one clinically normal horses; 380 hospitalized horses. Methods Total thyroxine (TT4), free thyroxine by equilibrium dialysis (fT4D), total triiodothyronine (TT3), free triiodothyronine (fT3), and TSH were measured in normal and hospitalized horses. Disease severity was categorized as mild, moderate, or severe by both subjective and objective criteria. Results Negative correlations existed between all THs, except TSH, and objective illness severity scores. These scores also increased with each subjective disease severity category. TT3 and fT3 were decreased with mild disease. TT3 progressively decreased more with moderate and severe disease. TT4 and fT4D remained normal with mild disease, but decreased progressively with disease severity. TSH increased with mild disease, but remained normal with moderate or severe disease. Horses that died or were euthanized had lower concentrations of all THs, except TSH, when compared with those that lived. In horses that received >3 doses of NSAIDs, corticosteroids, or heparin compared to 0–3 doses, TT3 and TT4 were decreased, whereas fT4D and TSH remained normal. There were minimal TH changes in horses that were not eating. Conclusions and Clinical Importance Thyroid hormones decrease in horses with systemic disease. TT3 decreases first, followed by TT4 and fT4D. TSH fails to increase proportionally to the changes in THs, indicating hypothalamic–pituitary axis dysregulation. NSAIDs, corticosteroids, heparin, and fasting have less effect on THs compared with disease severity.

Thyroid Function and Dysfunction in Term and Premature Equine Neonates

Background This study was performed to compare thyroid function of premature foals to term foals. Hypothesis Premature foals are more markedly hypothyroxinemic than expected for their severity of illness alone. Animals Twenty clinically normal term foals; 28 sick, hospitalized term foals; 24 sick, hospitalized premature foals. Methods Thyroid hormones (TH) and thyrotropin (TSH) were measured, both at rest and in response to thyrotropin‐releasing hormone (TRH), in the 3 groups of foals. Clinical and clinicopathologic data were recorded. Results Normal foals had high TH at birth, which decreased over the first month into the normal reference range for adult horses. TSH was within the normal adult reference range soon after birth, and did not change over time. At 24–36 hours of age, triiodothyronine (T3) was significantly lower in both premature and term hospitalized foals compared to normal foals; premature foals were not different from term hospitalized foals. Thyroxine (T4) was not different between normal and term hospitalized foals, but was significantly lower than in premature foals of both of these groups. TSH was not different among the 3 groups. TRH stimulation tests identified significant differences in T4 among all 3 groups of foals, whereas T3 was similar in premature and term hospitalized foals and different from normal foals. TSH response to TRH was significantly higher in premature foals compared to normal foals. Conclusions and Clinical Importance The hypothalamic‐pituitary‐thyroid axis is different in foals compared to adult horses. Sick foals exhibit nonthyroidal illness syndrome. Premature foals are more markedly hypothyroxinemic than can be accounted for by their severity of illness alone.

Outbreak of Lawsonia intracellularis on a Standardbred breeding farm in North Carolina

Summary Lawsonia intracellularis is a cause of protein-losing enteropathy in weanling foals commonly causing signs including diarrhoea, oedema and unthrifty appearance. It has previously been reported as sporadic cases throughout the USA, Canada and Europe. Only recently have outbreaks on a single farm location been reported. The cases reported here are an example of multiple foals on a single farm testing serologically positive for L. intracellularis. These foals ranged in severity from asymptomatic to severely hypoproteinaemic and septic; however, none of the foals ever displayed diarrhoea, which is the most common presenting sign of this disease process.

Extreme lymphocytosis with myelomonocytic morphology in a horse with diffuse large B-cell lymphoma.

An 11-year-old, 443-kg Haflinger mare was presented to the North Carolina State University Veterinary Teaching Hospital with a 2-week history of lethargy and a 3-day duration of anorexia, pyrexia, tachycardia, and ventral edema. Severe pitting edema, peripheral lymphadenopathy, and a caudal abdominal mass were noted on physical examination. An extreme leukocytosis (154.3 × 103 /μL) and microscopic hematologic findings suggestive of myelomonocytic leukemia were observed. Serum protein electrophoresis revealed a monoclonal gammopathy and urine protein electrophoresis revealed a monoclonal light chain proteinuria. Necropsy and histopathology confirmed widespread neoplastic infiltration in many organs with a heterogenous population of cells; there was no apparent evidence of bone marrow involvement. Immunohistochemistry confirmed presence of a majority of B cells with a limited antigen expression, admixed with a lower number of T cells. Molecular clonality analysis of IgH2, IgH3, and kappa-deleting element (KDE, B cell) on whole blood and KDE on infiltrated tissues revealed clonal rearrangements, and the KDE intron clones that amplified in blood and in infiltrated tissue were identical. In contrast, the clonality analysis of T-cell receptor γ revealed no clonality on blood cells and infiltrated tissues. In conjunction with the histopathologic changes, the lesion was interpreted to be composed of neoplastic B cells with a reactive T-cell population. Polymerase chain reaction testing for equine herpes virus 5 was negative. The final diagnosis was diffuse large B-cell lymphoma with a marked hematogenous component.

A mutation in the canine gene encoding folliculin-interacting protein 2 (FNIP2) associated with a unique disruption in spinal cord myelination.

Novel mutations in myelin and myelin‐associated genes have provided important information on oligodendrocytes and myelin and the effects of their disruption on the normal developmental process of myelination of the central nervous system (CNS). We report here a mutation in the folliculin‐interacting protein 2 (FNIP2) gene in the Weimaraner dog that results in hypomyelination of the brain and a tract‐specific myelin defect in the spinal cord. This myelination disruption results in a notable tremor syndrome from which affected dogs recover with time. In the peripheral tracts of the lateral and ventral columns of the spinal cord, there is a lack of mature oligodendrocytes. A genome‐wide association study of DNA from three groups of dogs mapped the gene to canine chromosome 15. Sequencing of all the genes in the candidate region identified a frameshift mutation in the FNIP2 gene that segregated with the phenotype. While the functional role of FNIP2 is not known, our data would suggest that production of truncated protein results in a delay or failure of maturation of a subpopulation of oligodendrocytes. GLIA 2014;62:39–51

Polyomavirus-Associated Nephritis in 2 Horses

Polyomaviruses produce latent and asymptomatic infections in many species, but productive and lytic infections are rare. In immunocompromised humans, polyomaviruses can cause tubulointerstitial nephritis, demyelination, or meningoencephalitis in the central nervous system and interstitial pneumonia. This report describes 2 Standardbred horses with tubular necrosis and tubulointerstitial nephritis associated with productive equine polyomavirus infection that resembles BK polyomavirus nephropathy in immunocompromised humans.