Measurement of ascorbic acid concentration and glutathione peroxidase activity in biological samples collected from horses with recurrent airway obstruction.

OBJECTIVE: To measure the ascorbic acid (AA) concentration in bronchoalveolar lavage fluid (BALF) and cellular glutathione peroxidase (cGPx) activity in RBCs and WBCs from peripherally obtained blood and in cells from BALF to determine whether differences existed between the 2 major redox systems in recurrent airway obstruction (RAO)-affected and -nonaffected (control) horses and between systemic and local pulmonary responses in the glutathione redox system. ANIMALS: 16 adult horses in pairs: 8 healthy (control) and 8 RAO-affected horses. PROCEDURES: Physical examination data and biological samples were collected from horses before (remission), during, and after (recovery) environmental challenge with dusty straw and hay. At each stage, BALF cell AA concentration and RBC, WBC, and BALF cell cGPx activity were measured. RESULTS: Compared with control horses, RAO-affected horses had significantly higher cGPx activity in RBCs at all points and in WBCs during remission and challenge. The BALF cell cGPx activity was higher in RAO-affected horses during recovery than during remission The BALF cell AA concentration did not differ significantly in control horses at any point, but total and free AA concentrations were significantly lower in RAO-affected horses during the challenge period than during remission and recovery periods. CONCLUSIONS AND CLINICAL RELEVANCE: High cGPx activity suggested this redox system was upregulated during exposure to dusty straw and hay to combat oxidative stress, as AA was depleted in RAO-affected horses. The relative delay and lack of comparative increase in cGPx activity within the local environment (represented by BALF cells), compared with that in RBCs and WBCs, might contribute to disease in RAO-affected horses.

Comparison of serum iohexol clearance and plasma creatinine clearance in clinically normal horses.

Objective-To determine whether a limited sampling time method based on serum iohexol clearance (Cl(iohexol)) would yield estimates of glomerular filtration rate (GFR) in clinically normal horses similar to those for plasma creatinine clearance (Cl(creatinine)). Animals-10 clinically normal adult horses. Procedures-A bolus of iohexol (150 mg/kg) was administered IV, and serum samples were obtained 5, 20, 40, 60, 120, 240, and 360 minutes after injection. Urinary clearance of exogenous creatinine was measured during three 20-minute periods. The GFR determined by use of serum Cl(iohexol) and plasma Cl(creatinine) was compared with limits of agreement plots. Results-Values obtained for plasma Cl(creatinine) ranged from 1.68 to 2.69 mL/min/kg (mean, 2.11 mL/min/kg). Mean serum Cl(iohexol) was 2.38 mL/min/kg (range, 1.95 to 3.33 mL/min/kg). Limits of agreement plots indicated good agreement between the methods. Conclusions and Clinical Relevance-Use of serum Cl(iohexol) yielded estimates of GFR in clinically normal adult horses similar to those for plasma Cl(creatinine). This study was the first step in the evaluation of the use of serum Cl(iohexol) for estimating GFR in adult horses.

Immunodeficiency disorders in horses.

Immunodeficiencies are characterized as primary (genetic) or secondary (acquired). Primary immunodeficiencies are relatively uncommon; however, clinically, they present a significant challenge to the practitioner, especially if the underlying disorder goes unrecognized. Secondary immunodeficiencies may present at any age, but failure of passive transfer in neonatal foals is most commonly encountered. This article provides a general overview of clinical signs and diagnosis of primary and secondary immunodeficiencies currently recognized in horses.

Diagnostic equine serology.

This article is presented with two main goals: (1) to provide equine clinicians with a resource for identifying types of serum tests available and (2) to outline briefly the necessary sample type, assay principle, and relative strengths and weakness of the various methods. Specific etiologies are presented and grouped by clinical diagnosis categories, along with brief comments concerning each disorder and its relevant diagnostic assays. This organization provides an abstracted list of infectious disorders commonly considered for the various clinical presentations and a summary of available serologic tests for narrowing the differential diagnosis list. The reader is also provided with a list of specific laboratories that perform the diagnostic assay for the mentioned disorders.

Blood proteins and inflammation in the horse.

Activation of the host response to infection, the "acute-phase response," is a highly organized physiologic reaction that includes changes in concentrations of plasma acute-phase proteins (APPs). The APPs are increasingly being used as markers for prognosis and monitoring response to therapy along with general determinants of equine health. Use of APPs in veterinary medicine is becoming more widespread as more commercial diagnostic kits are being validated. This article reviews the salient features of APPs and examines their current application and potential utility in equine inflammatory disorders.

Mycoplasma haemolamae infection in a 4-day-old cria: support for in utero transmission by use of a polymerase chain reaction assay.

Blood smear examination in a 4-day-old alpaca revealed massive erythrocyte parasitism by Mycoplasma haemolamae. Blood collected from both the nonparasitemic dam and the cria were positive for M. haemolamae by polymerase chain reaction (PCR) analysis. These findings suggest in utero transmission of M. haemolamae in camelids, even when the dam is not parasitemic.

Effects of feeding large amounts of grain on colonic contents and feces in horses.

OBJECTIVE: To assess changes in systemic hydration, concentrations of plasma electrolytes, hydration and physical properties of colonic contents and feces, and gastrointestinal transit in horses with access to large amounts of grain. ANIMALS: 6 horses with right dorsal colon (RDC) fistulas. PROCEDURE: In a crossover design, horses were alternately fed 1 of 3 diets: orchard grass hay ad libitum after being adapted to this diet for at least 5 days, orchard grass hay ad libitum and 4.55 kg of grain offered every 12 hours after being adapted to orchard grass hay ad libitum for at least 5 days, or orchard grass hay ad libitum and 4.55 kg of grain offered every 12 hours after being adapted to this diet for at least 5 days. Physical examinations were performed and samples of blood, colonic contents, and feces were collected every 6 hours during a 48-hour observation period. RESULTS: Grain ingestion had several effects, including changes in the concentrations of electrolytes in plasma; RDC contents became more homogenous, dehydrated, foamy, and less dense; RDC contents flowed spontaneously when the cannula was opened; RDC contents expanded when heated in an oven; and feces became fetid and less formed. Horses did not have any clinical signs of colic, endotoxemia, or laminitis. CONCLUSIONS AND CLINICAL RELEVANCE: Changes observed in the colonic contents and feces may be explained by the large amounts of hydrolyzable carbohydrates provided by grain. Access to large amounts of grain may increase the risk of tympany and displacement of the large intestine.

Effects of enteral and intravenous fluid therapy, magnesium sulfate, and sodium sulfate on colonic contents and feces in horses.

OBJECTIVE: To assess changes in systemic hydration, concentrations of electrolytes in plasma, hydration of colonic contents and feces, and gastrointestinal transit in horses treated with IV fluid therapy or enteral administration of magnesium sulfate (MgSO4), sodium sulfate (NaSO4), water, or a balanced electrolyte solution. ANIMALS: 7 horses with fistulas in the right dorsal colon (RDC). PROCEDURE: In a crossover design, horses alternately received 1 of 6 treatments: no treatment (control); IV fluid therapy with lactated Ringer's solution; or enteral administration of MgSO4, Na2SO4, water, or a balanced electrolyte solution via nasogastric intubation. Physical examinations were performed and samples of blood, RDC contents, and feces were collected every 6 hours during the 48 hour-observation period. Horses were muzzled for the initial 24 hours but had access to water ad libitum. Horses had access to hay, salt, and water ad libitum for the last 24 hours. RESULTS: Enteral administration of a balanced electrolyte solution and Na2SO4 were the best treatments for promoting hydration of RDC contents, followed by water. Sodium sulfate was the best treatment for promoting fecal hydration, followed by MgSO4 and the balanced electrolyte solution. Sodium sulfate caused hypocalcemia and hypernatremia, and water caused hyponatremia. CONCLUSIONS AND CLINICAL RELEVANCE: Enteral administration of a balanced electrolyte solution promoted hydration of RDC contents and may be useful in horses with large colon impactions. Enteral administration of either Na2SO4 or water may promote hydration of RDC contents but can cause severe electrolyte imbalances.

Evaluation of iohexol clearance used to estimate glomerular filtration rate in clinically normal foals.

OBJECTIVE: To determine whether pharmacokinetic analysis of data derived from a single i.v. dose of iohexol could be used to predict creatinine clearance and evaluate simplified methods for predicting serum clearance of iohexol with data derived from 2 or 3 blood samples in clinically normal foals. ANIMALS: 10 healthy foals. PROCEDURE: Serum disposition of iohexol and exogenous creatinine clearance was determined simultaneously in each foal (5 males and 5 females). A 3-compartment model of iohexol serum disposition was selected via standard methods. Iohexol clearance calculated from the model was compared with creatinine clearance. Separate limited-sample models were created with various combinations of sample times from the terminal slope of the plasma versus time profile for iohexol. Correction factors were determined for the limited-sample models, and iohexol clearance calculated via each method was compared with exogenous creatinine clearance by use of method comparison techniques. RESULTS: Mean exogenous creatinine clearance was 2.17 mL/min/kg. The disposition of iohexol was best described by a 3-compartment open model. Mean clearance value for iohexol was 2.15 mL/min/kg and was not significantly different from mean creatinine clearance. A method for predicting serum iohexol clearance based on a 2-sample protocol (3- and 4-hour samples) was developed. CONCLUSIONS AND CLINICAL RELEVANCE: Iohexol clearance can be used to predict exogenous creatinine clearance and can be determined from 2 blood samples taken after i.v. injection of iohexol. Appropriate correction factors for adult horses and horses with abnormal glomerular filtration rate need to be determined.

Effects of the insulin sensitizing drug, pioglitazone, and lipopolysaccharide administration on markers of systemic inflammation and clinical parameters in horses.

Equine metabolic syndrome (EMS) is a condition of obese horses characterized by insulin resistance, systemic inflammation, and an increased risk of laminitis. The pathogenesis of EMS is thought, in part, to be due to inflammatory proteins produced by adipose tissue. Reducing inflammation may decrease the incidence of laminitis in horses with EMS. Pioglitazone hydrochloride, a thiazolidinedione, has efficacy to reduce obesity associated inflammation in humans. Eight normal, adult, horses were administered 1mg/kg pioglitazone for 14 days, and eight horses served as controls. Physical examination and hematologic variables, transcript abundance of pro-inflammatory cytokines in skeletal muscle and adipose tissue, and circulating concentrations of the acute phase protein, serum amyloid A and pro-inflammatory cytokine, TNF-α were assessed prior to, and following, an LPS infusion (35 ng/kg). The objective was to determine if pre-treatment with pioglitazone would mitigate the development of inflammation and associated clinical markers of inflammation following LPS administration. Lipopolysaccharide administration induced systemic inflammation, as assessed by clinical and hematological aberrations, increased TNF-α, SAA and adipose tissue IL-6 mRNA abundance, however no mitigating effects of pioglitazone were detected. A longer treatment period or higher dose might be indicated for future experiments.

Effects of acute hyperinsulinemia on inflammatory proteins in horses.

Laminitis is a painful, inflammatory disease of the equine hoof that often results in euthanasia. Elevated plasma insulin concentrations are a predictive factor for laminitis, and in previously healthy horses and ponies, laminitis was induced by infusion of insulin. Thus, we chose to determine if an infusion of insulin would increase plasma concentrations of inflammatory cytokines and cytokine mRNA abundance in subcutaneous adipose tissue, skeletal muscle, and white blood cells. Ten mature Thoroughbred mares received an insulin infusion that elevated plasma insulin concentrations for 6h or an equivalent volume of isotonic saline in a switchback design. Insulin infusion altered plasma concentrations of both TNF (P=0.037) and IL-6 (P=0.044), but did not result in consistent changes to either skeletal muscle or adipose tissue cytokine mRNA. Insulin may be involved in the production of inflammatory cytokines, and this could be a mechanism for insulin increasing the risk of laminitis.

De novo fatty acid synthesis and NADPH generation in equine adipose and liver tissue.

The lipogenic capacities of equine liver and adipose tissue explants were investigated in vitro. Preference for glucose or acetate as the primary carbon source for de novo fatty acid synthesis was determined using (14)C labeled substrates. Additional aims included determining the relative contribution of NADPH generating pathways to reducing equivalent generation and comparing the lipogenic activity of two adipose depots, mesenteric and subcutaneous harvested from the crest region of the neck. Mesenteric adipose tissue had greater lipogenic activity than subcutaneous adipose tissue, and liver tissue showed minimal (14)C incorporation into fatty acids, indicating a low hepatic lipogenic capacity. Acetate was found to be the primary carbon source for fatty acid synthesis due to both the appearance of the (14)C label in the lipid fraction and the low activity of ATP-citrate lyase. Finally, the pentose phosphate and isocitrate dehydrogenase enzymes contributed to NADPH production in equine adipose tissue.

Imaging diagnosis--Dorsal mediastinal T-cell lymphoma in an alpaca.

A 14-year-old male alpaca had refractory pleural effusion. The cause of the effusion was not apparent either radiographically or sonographically, or following a pleural fluid cytologic examination. Using computed tomographic (CT) examination, a dorsal paravertebral mass was identified and similar masses were found in the cranial mediastinum, retroperitoneal space, and adjacent to the hepatic entry of the portal vein. The histopathologic diagnosis was multicentric T-cell lymphoma. CT examination may prove to be a valuable imaging modality in the localization and staging of neoplasia in new world camelids.