Pharmacokinetics and clinical effects of a subanesthetic continuous rate infusion of ketamine in awake horses

OBJECTIVE: To determine the pharmacokinetics and clinical effects of a subanesthetic, continuous rate infusion of ketamine administered to healthy awake horses. ANIMALS: 8 adult horses. PROCEDURES: Ketamine hydrochloride was administered to 2 horses, in a pilot study, at rates ranging from 0.4 to 1.6 mg/kg/h for 6 hours to determine an appropriate dose that did not cause adverse effects. Ketamine was then administered to 6 horses for a total of 12 hours (3 horses at 0.4 mg/kg/h for 6 hours followed by 0.8 mg/kg/h for 6 hours and 3 horses at 0.8 mg/kg/h for 6 hours followed by 0.4 mg/kg/h for 6 hours). Concentration of ketamine in plasma, heart rate, respiratory rate, blood pressure, physical activity, and analgesia were measured prior to, during, and following infusion. Analgesic testing was performed with a modified hoof tester applied at a measured force to the withers and radius. RESULTS: No signs of excitement and no significant changes in the measured physiologic variables during infusion rates of 0.4 and 0.8 mg of ketamine/kg/h were found. At 6 hours following infusions, heart rate and mean arterial pressure were decreased, compared with preinfusion measurements. An analgesic effect could not be demonstrated during or after infusion. Pharmacokinetic variables for 0.4 and 0.8 mg/kg/h infusions were not significantly different. CONCLUSIONS AND CLINICAL RELEVANCE: Ketamine can be administered to awake horses at 0.4 or 0.8 mg/kg/h without adverse behavioral effects. The observed pharmacokinetic values are different than those reported for single-dose IV bolus administration of this drug.     

Comparison of radioimmunoassay and enzyme-linked immunoassay for the measurement of progestogen in equine plasma and milk

Milk and plasma samples were obtained every 48 hours from eight pony mares for 40 days after foaling. Progestogen concentrations in milk and plasma were measured using an enzyme-linked immunoassay (ELISA) and compared with radioimmunoassay of the plasma. In general the three assays showed similar trends in progestogen concentration changes but absolute values varied considerably. Difficulty could occur in interpreting the results from single samples taken at times when progestogen concentrations were either rising (ie, after ovulation) or falling. ELISA could be used on plasma obtained by allowing the erythrocytes to settle for 30 minutes at room temperature or for two days at 4 degrees C.     

A preliminary investigation on the use of thermodilution and echocardiography as an assessment of cardiac function in the cat.

A technique for the determination of cardiac output in the cat by the thermal dilution method is described. The values of cardiac output assessed by thermal dilution and the values of left ventricular function assessed echocardiographically are compared. Values of cardiac output obtained by thermal dilution compare favourably with values obtained by other investigators by indicator dye dilution, the Fick method and electromagnetic flowmeter technique. The technique of thermal dilution in the cat was consistent and simple to perform. The calculation of ventricular volumes and cardiac output echocardiographically using formulae suggested in man was unsuccessful. Such formulae based on assumptions of cardiac shape and contractility do not appear valid in the cat. Statistical analysis demonstrated a positive correlation between the cardiac output determined by thermodilution and the left ventricular diastolic and systolic dimensions determined echocardiographically. A positive correlation was also shown between the cardiac output and the cardiac index, the left ventricular diastolic dimension and the left ventricular systolic dimension and the percent change in minor diameter and the velocity of circumferential fibre shortening. A negative correlation existed between the left ventricular systolic dimension and the velocity of circumferential fibre shortening and the ejection time and the velocity of circumferential fibre shortening.     

Echocardiographic assessment of cats anesthetized with xylazine-sodium pentobarbital.

Left ventricular echocardiographic parameters in cats were recorded, measured and analyzed to study the effects of a combination of xylazine and sodium pentobarbital on left ventricular function. The depressant effects of a combination of xylazine and sodium pentobarbital on the left ventricular dimension at end diastole, the percent change in minor diameter and the velocity of circumferential fibre shortening were compared to echocardiographic values of unanesthetized cats. No change in heart rate was noted. Stroke volume and cardiac output were depressed.     

Glycogen depletion patterns in horses performing maximal exercise

Muscle biopsy samples were collected from the left middle gluteal muscle of horses participating in competitive barrier trials. Twelve horses were biopsied the day before and within 30 minutes of completion of an 800 m barrier trial. A further six horses were sampled the day before, and within 30 minutes of, completion of a 1200 m barrier trial. Serial muscle sections were examined histochemically for myosin adenosine triphosphatase activity after acid preincubation, to demonstrate type I, IIA and IIB fibres. The glycogen content in the individual fibres was assessed using the periodic acid Schiff (PAS) reaction. Total glycogen in muscle was measured fluorimetrically after hydrolysis to glucose. Significant decreases in total muscle glycogen levels of 167.1 +/- 22.2 and 158.1 +/- 23.2 mmoles glucose units kg-1 (dry weight) (mean +/- standard error) occurred from pre- to post trial samples for horses in both 800 and 1200 m trials respectively. There were no significant differences between the decreases in total muscle glycogen from horses in either 800 m or 1200 m trials. In both 800 m and 1200 m trials there was a significant decrease in the percentage of type IIA and IIB fibres classified as having high PAS staining intensity, and a significant increase in the percentage of fibres classified as having medium staining intensity when samples taken after the trial were compared to those taken before the trial.     

EVALUATION OF A HARDJO-POMONA VACCINE TO PREVENT LEPTOSPIRURIA IN CATTLE EXPOSED TO A NATURAL CHALLENGE WITH LEPTOSPIRA INTERROGANS SEROVAR HARDJO

SUMMARY The efficacy of a vaccine against Leptospira interrogans serovar pomona and Leptospira interrogans serovar hardjo was evaluated in a group of dairy heifers that were serologically negative at the time of vaccination and later subjected to natural challenge with L. interogans serovar hardjo. Thirty-nine heifers were vaccinated twice, at a one-month interval, with a commercially prepared bivalent vaccine, while 43 unvaccinated heifers were used as controls. After vaccination, microscopic agglutination (MA) titres of serums to L. interrogans serovar hardjo ranged from 32 to 512, and those to L. interrogans serovar pomona ranged from 32 to 2048. Titres resulting from vaccination were short-lived and after the first vaccination the serums of 95% of vaccinated heifers did not react in the MA test by 24 weeks. The first indication of infection in the heifers was noted at week 6, and by week 16, elevated MA titres (≥128) to L. interrogans serovar hardjo had occurred in 62% of unvaccinated heifers and had increased to 85% by week 24. At week 18, 18% of the vaccinated heifers and 56% of the unvaccinated heifers had leptospiruria (p<0.01); after 22 weeks, 13% of the vaccinated heifers and 58% of the unvaccinated heifers showed evidence of leptospiruria (p<0.01).     

Changes in liver glycogen of broilers during coccidiosis

Liver glycogen levels of broilers infected with Eimeria acervulina, E. brunetti, or E. tenella fell during the acute phase of the infection with the maximum effect at 5–6 days post-inoculation (DPI). During the early recovery phase (6–8 DPI), liver glycogen levels in the E. acervulina-infected birds increased to levels up to 3 times greater than those found in uninoculated control birds. A lesser increase was occasionally seen in E. tenella-infected birds. Pair feeding studies showed that the decrease in liver glycogen was not related to the amount of feed consumed. The magnitude of the glycogen overshoot at 7 DPI was not related to the depression of weight gain at 5 and 6 DPI. When feed was withheld from birds, liver glycogen levels of uninoculated control birds fell rapidly within 1 h after feed withdrawal. In birds infected with E. acervulina, liver glycogen levels remained high even after 3 h starvation. Injection of glucagon indicated that glycogen could be mobilized in both infected and uninfected birds.