Efficacy of an Epidural Combination of Morphine and Detomidine in Alleviating Experimentally Induced Hindlimb Lameness in Horses

Amphotericin B-induced synovitis of the left tarsocrural joint was used to create a grade 3 of 4 lameness in 11 horses. Caudal epidural catheters were placed and advanced to the lumbosacral region. Baseline heart and respiratory rates were recorded and horses were videotaped at a walk and trot. Morphine sulphate (0.2 mg/kg) and detomidine hydrochloride (30 μg/kg) were administered to treated horses (n = 8) through the epidural catheter; an equivalent volume of physiologic saline solution was administered to control horses (n = 3) through the catheter. At hourly intervals after epidural injection for a total of 6 hours, heart and respiratory rates were recorded, and horses were videotaped walking and trotting. At the end of the observation period, video recordings were scrambled onto a master videotape. Lamenesses were scored by three investigators unaware of group assignment or treatment time. Lameness scores, heart rates, and respiratory rates were compared between groups using repeated measures analysis of variance. There was a significant decrease in lameness score after treatment with epidural morphine and detomidine ( P =.0003); average lameness scores of treated horses were less than grade 1 at each hourly observation for 6 hours after drug administration. Early in the observation period, heart rates significantly increased in control horses and decreased in treated horses ( P =.03). A similar trend occurred for respiratory rates ( P =.07). Results of this study demonstrate that epidural administration of a combination of morphine and detomidine is capable of providing profound hindlimb analgesia in horses.     

Cardiovascular Effects of Intravenous Sodium Penicillin, Sodium Cefazolin, and Sodium Citrate in Awake and Anesthetized Horses

Sodium penicillin, sodium cefazolin, and sodium citrate were administered to six adult horses on separate occasions, when awake and during anesthesia. The order of administration was randomized and studies were separated by a minimum of 7 days. Arterial blood pressure decreased significantly (less than 0.05) from control 5 minutes after intravenous (IV) sodium penicillin in awake and anesthetized horses. Systolic arterial blood pressure remained significantly (less than 0.05) decreased 10 minutes after IV sodium penicillin in anesthetized horses. Sodium cefazolin and sodium citrate did not significantly affect any of the measured cardiovascular variables. Although the changes in arterial blood pressure were small (8-15 mm Hg), monitoring of arterial blood pressure is advised when sodium penicillin is administered IV to anesthetized horses.     

Plasma Concentration of Glucosamine and Chondroitin Sulfate in Horses after an Oral Dose

This study was conducted to study absorption of glucosamine (GlucN) and chondroitin sulfate (CS) in horses immediately after feeding. Six mature mares were used in a replicated 3 × 3 Latin-square-designed experiment. The experiment consisted of three 15-day periods, which included 10 days of diet adaptation followed by a 5-day sampling period. Blood was drawn after feeding on one day during each sampling period. Horses were fed a control diet (40% hay, 60% concentrate) balanced to meet NRC requirements for maintenance of mature horses (NRC, Nutrient requirements of horses, 1989). In one experimental diet, 2.0 g CS and 5.5 g GlucN were added to the basal ration at each feeding. In the other experimental diet, 3.5 g CS and 8.5 g GlucN were added to the basal ration at each feeding. After collections, blood was centrifuged and plasma was harvested and stored until analyzed for the presence of each compound. Analyses for plasma GlucN were performed using high-performance liquid chromatography. CS in the plasma was analyzed using a color reagent, dimethylmethylene blue, followed by ultraviolet spectrophotometry. There were no significant differences (P < .05) in the concentration of either CS or GlucN in plasma, when comparing the three different diets. This leads to a conclusion that these compounds were not absorbed intact through the intestinal wall into the bloodstream. This poses a question as to whether oral forms of these compounds are absorbed and are able to migrate to joints through the blood to improve joint function.     

A Reproducible Venous Thrombosis Model in Horses Induced by the Combination of an Endothelial Lesion and Blood Flow Stasis

Because of the high incidence of thromboembolic diseases in humans, experimental models of thrombosis have been widely developed in different animal species. The pathogenesis of thrombosis is associated with three components, first outlined by Virchow in 1856: vessel injury, stasis, and hypercoagulability. Based on this concept, the purpose of the present investigation was to create an innovative model of jugular thrombophlebitis in horses that included components of Virchow's triad and excluded surgical procedures. Eighteen horses were subjected to blood vessel injury through the coadministration of sclerosing agents (glucose and ethanolamine oleate) and transitory occlusion of the jugular flow by manual compression. Thrombus formation was followed by ultrasonography imaging, and all horses developed jugular thrombophlebitis, showing that the proposed model was effective. Once occlusive thrombophlebitis was induced, jugular venous pressure cranial to the lesion was evaluated and yielded increased values, suggesting cephalic hypertension. Biochemical tests were performed to verify hepatotoxicity and nephrotoxicity after the ethanolamine injection, but no abnormalities were observed. Five horses were then euthanized to evaluate the vascular, hepatic, and renal tissues. The jugular vein wall had increased thickness, inflammatory cell influx, endothelial destruction, and thrombus firmly adhered to the vessel intima. Histological evaluation of the hepatic and renal tissues was normal. The present thrombophlebitis model in the jugular vein of the horse is simple and reproducible, providing a useful tool for investigating acute and chronic venous thrombosis because the model allows evaluation of different aspects of the prevention, pathogenesis, and treatment of this disease.     

Effects of Intermittent Positive Pressure Ventilation on Cardiopulmonary Function in Horses Anesthetized with Total Intravenous Anesthesia Using Combination of Medetomidine,Lidocaine, Butorphanol and Propofol (MLBP-TIVA)

Effects of intermittent positive pressure ventilation (IPPV) on cardiopulmonary function were evaluated in horses anesthetized with total intravenous anesthesia using constant rate infusions of medetomidine (3.5 µg/kg/hr), lidocaine (3 mg/kg/hr), butorphanol (24 µg/kg/hr) and propofol (0.1 mg/kg/min) (MLBP-TIVA). Five horses were anesthetized twice using MLBP-TIVA with or without IPPV at 4-week interval (crossover study). In each occasion, the horses breathed 100% oxygen with spontaneous ventilation (SB-group, n=5) or with IPPV (CV-group, n=5), and changes in cardiopulmonary parameters were observed for 120 min. In the SB-group, cardiovascular parameters were maintained within acceptable ranges (heart rate: 33–35 beats/min, cardiac output: 27–30 l/min, mean arterial blood pressure [MABP]: 114–123 mmHg, mean pulmonary arterial pressure [MPAP]: 28–29 mmHg and mean right atrial pressure [MRAP]: 19–21 mmHg), but severe hypercapnea and insufficient oxygenation were observed (arterial CO₂ pressure [PaCO₂]: 84–103 mmHg and arterial O₂ pressure [PaO₂]: 155–172 mmHg). In the CV-group, normocapnea (PaCO₂: 42–50 mmHg) and good oxygenation (PaO₂: 395–419 mmHg) were achieved by the IPPV without apparent cardiovascular depression (heart rate: 29–31 beats/min, cardiac output: 17–21 l /min, MABP: 111–123 mmHg, MPAP: 27–30 mmHg and MRAP: 15–16 mmHg). MLBP-TIVA preserved cardiovascular function even in horses artificially ventilated.     

Systemic,Renal, and Colonic Effects of Intravenous and Enteral Rehydration in Horses

Background

Intravenous (IV) and intragastric (IG) administration of fluid therapy are commonly used in equine practice, but there are limited data on the systemic, renal, and enteric effects.

Hypothesis

IV fluid administration will increase intestinal and fecal hydration in a rate‐dependent manner after hypertonic dehydration, but will be associated with significant urinary water and electrolyte loss. Equivalent volumes of IG plain water will result in comparatively greater intestinal hydration with less renal loss.

Animals

Six Thoroughbred geldings.

Methods

Experimental study. 6 by 6 Latin square design investigating constant rate IV administration at 50, 100, and 150 mL/kg/d over 24 hours in horses dehydrated by water deprivation. Equivalent volumes of IG plain water were administered by 4 bolus doses over 24 hours.

Results

Water deprivation resulted in a significant decrease in the percentage of fecal water, and increases in serum and urine osmolality. IV fluids administered at 100 and 150 mL/kg/d restored fecal hydration, but increasing the rate from 100 to 150 mL/kg/d did not confer any additional intestinal benefit, but did result in significantly greater urine production and sodium loss. Equivalent 24‐hour volumes of plain water resulted in greater intestinal water and less urine output.

Conclusions and Clinical Importance

IV polyionic isotonic fluids can be used to hydrate intestinal contents in situations where enteral fluids are impractical. IV fluids administered at three times maintenance are no more efficacious and might be associated with adverse physiological findings after withdrawal. Bolus dosing of IG water can be used to restore intestinal water with minimal adverse effects.     

Atrial and Ventricular Electrical and Contractile Remodeling and Reverse Remodeling Owing to Short‐Term Pacing‐Induced Atrial Fibrillation in Horses

Background: In humans, atrial fibrillation (AF) induces electrical, contractile, and structural remodeling leading to AF stabilization. Little is known about AF‐induced atrial remodeling in horses. Hypothesis: Induced AF produces rapid atrial electrical and contractile remodeling in horses. Animals: Six horses, 5 animals completed the study. Methods: Each horse was instrumented with a pulse generator and pacemaker to maintain AF by burst pacing and to study atrial and ventricular electrophysiology (AF cycle length [AFCL], AF duration, and atrial/ventricular effective refractory period [AERP/VERP] at different pacing cycle lengths [PCL]). Left atrial and ventricular contractile remodeling were assessed echocardiographically by calculation of fractional changes in atrial and ventricular dimensions, respectively, during the cardiac cycle. Measurements were performed at baseline, a 7‐day AF period and a 2‐day recovery period. Results: Atrial electrical and contractile remodeling could be demonstrated after 4 and 12 hours of AF, respectively. A progressive shortening of the AERP (261 ± 39–171 ± 18 ms at a PCL of 1,000 ms, P < .0001), an attenuation of the AERP rate adaptation, a decrease in AFCL (239 ± 39–194 ± 7 ms, P < .0001), and a decrease in atrial FS (12 ± 3% to 0 ± 2%, P < .05) occurred. AF duration increased progressively and became persistent in 2 animals. VERP did not change significantly. Upon restoration of sinus rhythm, values returned to baseline within 48 hours. Conclusions and Clinical Importance: Atrial electrical and contractile remodeling appears rapidly. After 7 days of AF, reverse remodeling occurred within 2 days. These observations suggest that early conversion of AF might be beneficial for success rate and early return to training.     

Outbreak of Lice in Horses: Epidemiology,Diagnosis, and Treatment

The aim of this study is to report an outbreak of lice (Bovicola equi) in horses in southern Brazil, focusing on epidemiology, diagnosis, and treatment. Twenty-three horses in a stud farm presented with intense itching, crusted lesions, focal alopecia, and scaly skin. The outbreak occurred during the winter and probably due to the absence of sanitary barriers on the property. The diagnosis was carried out based on clinical signs associated with macroscopic and microscopic visualization of lice identified as B. equi. The treatment was performed with a single dose of Fipronil (Topline® Merial Brasil, Campinas, São Paulo, Brazil) spray (0.5%), eliminating immature and adult stages of lice. The clinical signs caused by the lice in horses disappeared few days after treatment.     

Molecular Investigation of the Viral Kinetics of Equine Herpesvirus‐1 in Blood and Nasal Secretions of Horses after Corticosteroid‐Induced Recrudescence of Latent Infection

Background: Recrudescence of latent equine herpesvirus 1 (EHV‐1) with subsequent viral shedding via nasal secretions is a potential source of infection for susceptible horses and has been implicated in outbreaks occurring in closed populations. Objectives: To describe the viral kinetics of reactivated EHV‐1 in blood and nasal secretions from latently infected horses after administration of corticosteroids, and to study the infectious nature of reactivated EHV‐1 to sentinel horses. Animals: Eight healthy horses. Methods: Four horses infected 4 months previously with EHV‐1 received dexamethasone on 5 consecutive days. Four seronegative horses served as sentinels and had direct contact with the latently infected horses. All horses were monitored daily for development of clinical signs. Whole blood and nasal secretions were collected daily for molecular detection and cell culture of EHV‐1. Serum was collected weekly for the detection of antibodies against EHV‐1. Results: All horses in the latently infected group showed transient molecular detection of EHV‐1 in blood and nasal secretions, but only 1 horse developed fever. Three latently infected horses developed an increase in antibody concentrations against EHV‐l. Viral cultures remained negative for all latently infected horses after corticosteroid administration. None of the sentinel horses developed clinical signs, viremia, viral shedding, or seroconversion. Conclusions and Clinical Importance: EHV‐1 was successfully reactivated after corticosteroid administration in latently infected horses. However, transmission of reactivated virus to sentinel horses was unsuccessful. Failure to effectively transmit EHV‐1 to susceptible horses may have resulted from the low level and short period of viral shedding in latently infected horses.