Effect of age and training status on pharmacokinetics of flunixin meglumine in thoroughbreds

The effect of age and training status on the pharmacokinetics of flunixin meglumine was evaluated in 16 Thoroughbreds. Horses were assigned to 1 of 3 groups on the basis of age and training status: group A (n = 6), horses in active training and less than or equal to 5 years old; group B (n = 5), horses out of training for a minimum of 6 weeks and less than or equal to 5 years old; and group C (n = 5), horses out of training for at least 2 years and greater than or equal to 9 years old. After administration of 500 mg of flunixin meglumine IV, multiple serum and urine samples were obtained over 24 hours and assayed for flunixin by high-performance liquid chromatography. Although the mean distribution rate constant and volume of distribution were similar for the 3 groups, mean total body clearance and elimination rate constant were significantly (P less than 0.05) greater and half-life significantly (P less than 0.01) less in groups A and B, compared with group C. Differences in pharmacokinetic values were not observed between the horses in group A and B. In addition, the changes in clearance, elimination rate constant, and half-life of flunixin were found to significantly (P less than 0.05) correlate with age. The results of this investigation indicated that age, but not training status, influences disposition of flunixin meglumine in Thoroughbreds.     

Pharmacokinetics of flunixin meglumine in donkeys, mules, and horses

OBJECTIVE: To compare serum disposition of flunixin meglumine after i.v. administration of a bolus to horses, donkeys, and mules. ANIMALS: 3 clinically normal horses, 5 clinically normal donkeys, and 5 clinically normal mules. PROCEDURE: Blood samples were collected at time zero (before) and 5, 10, 15, 30, and 45 minutes, and at 1, 1.25, 1.5, 1.75, 2, 2.5, 2.75, 3, 3.5, 4, 4.5, 5, 5.5, 6, and 8 hours after i.v. administration of a bolus of flunixin meglumine (1.1 mg/kg of body weight). Serum was analyzed in duplicate by the use of high-performance liquid chromatography for determination of flunixin meglumine concentrations. The serum concentration-time curve for each horse, donkey, and mule were analyzed separately to estimate noncompartmental pharmacokinetic variables RESULTS: Mean (+/-SD) area under the curve for donkeys (646 +/- 148 minute x microg/ml) was significantly less than for horses (976 +/- 168 minute x microg/ml) or for mules (860 +/- 343 minute x microg/ml). Mean residence time for donkeys (54.6 +/- 7 minutes) was significantly less than for horses (110 +/- 24 minutes) or for mules (93 +/- 30 minutes). Mean total body clearance for donkeys (1.78 +/- 0.5 ml/kg/h) was significantly different from that for horses (1.14 +/- 0.18 ml/kg/h) but not from that for mules (1.4 +/- 0.5 ml/kg/h). Significant differences were not found between horses and mules for any pharmacokinetic variable. CONCLUSION AND CLINICAL RELEVANCE: Significant differences exist with regard to serum disposition of flunixin meglumine in donkeys, compared with that for horses and mules. Consequently, flunixin meglumine dosing regimens used in horses may be inappropriate for use in donkeys.     

Disposition of flunixin meglumine injectable preparation administered orally to healthy horses

An injectable preparation of flunixin meglumine was administered orally and intravenously at a dose of 1.1 mg/kg to six healthy adult horses in a cross-over design. Flunixin meglumine was detected in plasma within 15 min of administration and peak plasma concentrations were observed 45-60 min after oral administration. Mean bioavailability of the oral drug was 71.9 +/- 26.0%, with an absorption half-life of 0.76 h. The apparent elimination half-life after oral administration was 2.4 h. The injectable preparation of flunixin meglumine is suitable for oral administration to horses.     

Modulation of arachidonic acid metabolism in endotoxic horses: comparison of flunixin meglumine, phenylbutazone, and a selective thromboxane synthetase inhibitor

Two cyclooxygenase inhibitors (flunixin meglumine and phenylbutazone) and a selective thromboxane synthetase inhibitor were assessed in the management of experimental equine endotoxemia. Drugs or saline solution were administered to 16 horses 15 minutes before administration of a sublethal dose of endotoxin (Escherichia coli 055:B5). Plasma concentrations of thromboxane B2 (TxB2), prostacyclin (6-keto PGF1 alpha), plasma lactate, and hematologic values and clinical appearance were monitored for 3 hours after endotoxin administration. Pretreatment with flunixin meglumine (1 mg/kg of body weight) prevented most of the endotoxin-induced changes and correlated with a significant decrease in plasma TxB2 and 6-keto PGF1 alpha concentrations, compared with concentrations in nontreated horses (ie, pretreated with saline solution). Pretreatment with phenylbutazone (2 mg/kg) attenuated the effects of endotoxin and was associated with a brief, early, significant increase in plasma TxB2 concentrations, but not in plasma 6-keto PGF1 alpha concentrations. Pretreatment with the thromboxane synthetase inhibitor did not appear to clinically benefit the horses involved; however, arachidonic acid metabolism was redirected to prostacyclin production.     

Correlation of performance with endoscopic and radiographic assessment of epiglottic hypoplasia in racehorses with epiglottic entrapment corrected by use of contact neodymium:yttrium aluminum garnet laser

Epiglottic entrapment in 35 Thoroughbred and 44 Standardbred horses was corrected transendoscopically by use of a neodymium:yttrium aluminum garnet laser. Before surgery, the entrapped epiglottis was classified as hypoplastic or normal in each horse on the basis of endoscopic appearance alone. Using a digitizer, thyroepiglottic length was determined from lateral-view laryngeal radiographs. For 78 racehorses, earnings (less than $5,000 or greater than $5,000) were compared before and after surgery. Earnings category and racing performance after surgery were tested for association with endoscopically determined epiglottic hypoplasia and radiographically determined thyroepiglottic length. Endoscopy and radiography were useful methods of evaluating the epiglottis in horses with epiglottic entrapment. Mean (+/- SD) thyroepiglottic length for both breeds of horses with epiglottic entrapment was significantly (P = 0.0001) smaller (Thoroughbreds, 7.28 +/- 0.67 cm; Standardbreds, 7.21 +/- 0.62 cm), compared with thyroepiglottic length measured from control groups composed of clinically normal Thoroughbred (8.56 +/- 0.29 cm) and Standardbred (8.74 +/- 0.38 cm) racehorses. Both breeds of horses with epiglottic entrapment that had endoscopically apparent hypoplastic epiglottis had significantly (P less than 0.0001) smaller thyroepiglottic length (Thoroughbreds, 6.64 +/- 0.60 cm; Standardbred, 6.93 +/- 0.72 cm) than did horses with epiglottic entrapment that had endoscopically normal epiglottis (Throughbreds, 7.57 +/- 0.47 cm, Standardbreds, 7.36 +/- 0.50 cm). Significant difference was not detected in endoscopic appearance of the epiglottis among age, gender, or breed distributions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of flunixin meglumine or etodolac treatment on mucosal recovery of equine jejunum after ischemia

OBJECTIVE: To examine the effects of flunixin meglumine and etodolac treatment on recovery of ischemic-injured equine jejunal mucosa after 18 hours of reperfusion. ANIMALS: 24 horses. PROCEDURE: Jejunum was exposed to 2 hours of ischemia during anesthesia. Horses received saline (0.9% NaCl) solution (12 mL, i.v., q 12 h), flunixin meglumine (1.1 mg/kg, i.v., q 12 h), or etodolac (23 mg/kg, i.v., q 12 h). Tissue specimens were obtained from ischemic-injured and nonischemic jejunum immediately after ischemia and 18 hours after recovery from ischemia. Transepithelial electric resistance (TER) and transepithelial flux of tritium-labeled mannitol measured mucosal permeability. Denuded villous surface area and mean epithelial neutrophil count per mm2 were calculated. Western blot analysis for cyclooxygenase (COX)-1 and -2 was performed. Pharmacokinetics of flunixin and etodolac and eicosanoid concentrations were determined. RESULTS: Ischemic-injured tissue from horses treated with flunixin and etodolac had significantly lower TER and increased permeability to mannitol, compared with that from horses treated with saline solution. Epithelial denudation after ischemia and 18 hours after recovery was not significantly different among treatments. Both COX-1 and -2 were expressed in ischemic-injured and nonischemic tissues. Ischemia caused significant upregulation of both COX isoforms. Eicosanoid concentrations were significantly lower in tissues from flunixin and etodolac-treated horses, compared with that from horses treated with saline solution. CONCLUSIONS AND CLINICAL RELEVANCE: Flunixin and etodolac treatment retarded recovery of intestinal barrier function in jejunal mucosa after 18 hours of reperfusion, whereas tissues from horses treated with saline solution recovered baseline values of TER and permeability to mannitol.     

Endotoxin-induced bovine mastitis: arachidonic acid metabolites in milk and plasma and effect of flunixin meglumine

Arachidonic acid metabolites (AAM) were measured in milk and plasma during the course of acute endotoxin-induced mastitis in 12 lactating cows. Mastitis was induced by intramammary challenge exposure with 10 micrograms of Escherichia coli (026:B6) endotoxin. Endotoxin was injected into the teat cistern via the teat canal of a single randomly selected rear quarter of each cow. Concentrations of prostaglandin (PG) F2 alpha and thromboxane (Tx) B2 in fat-free unextracted milk and of 15-keto-13,14-dihydro-PGF2 alpha in plasma were measured by radioimmunoassay. Total production of AAM in milk was determined by measuring quarter milk production. The AAM were compared in 6 cows administered flunixin meglumine (1.1 mg/kg of body weight) and in 6 cows administered saline solution. Concentrations of TxB2 in milk were significantly (P less than 0.001) increased during the early course of acute mastitis in endotoxin-treated quarters of cows not administered flunixin meglumine. Peak concentrations of TxB2 in milk occurred at 8 hours after endotoxin inoculation. Flunixin meglumine treatment produced significant (P less than 0.05) reductions in milk TxB2 and plasma 15-keto-13,14-dihydro-PGF2 alpha concentrations. Concentrations of PGF2 alpha in milk and total PGF2 alpha and TxB2 production per quarter per milking were not significantly influenced by endotoxin challenge or by flunixin meglumine treatment.     

Pharmacokinetics of flunixin in mature heifers following multiple intravenous administration

The pharmacokinetics of flunixin meglumine was determined after its multiple (altogether 4 doses at 24-hours intervals) intravenous administration at a dose of 2.2 mg/kg body weight in six mature clinically healthy heifers. Plasma flunixin and its metabolite 5-hydroxyflunixin concentrations were analyzed with high-pressure liquid chromatography using an assay with a lower limit detection of 0.03 microg/ml for both substances. Plasma concentrations versus time curves were described by a two compartment open model. Mean plasma flunixin concentrations were similar on day 1 and 4, and than rapidly decreased (within 2 hours) from initial concentrations higher than 10 microg/ml to the concentrations lower than 1 microg/ml. The distribution phase of flunixin was short (t0.5 alpha = 0.29 +/- 0.16 and 0.18 +/- 0.04 on day 1 and 4, respectively) and the elimination phase was more prolonged (t0.5 beta = 3.30 +/- 0.60 and 3.26 +/- 0.22 on day 1 and 4, respectively). The mean residence time of flunixin was similar on day 1 (1.83 +/- 0.83) and 4 (1.88 +/- 0.46), and for 5-hydroxyflunixin this parameter was insignificantly (P > 0.05) higher on day 1 (5.49 +/- 2.22) as compared to that found on day 4 (3.99 +/- 2.17). The clearance of flunixin was similar on both examined days (0.23 +/- 0.12 on day 1 and 0.31 +/- 0.15 on day 4), and for 5-hydroxyflunixin was insignificantly (P > 0.05) lower on day 1 (2.37 +/- 1.21) as compared to that determined on day 4 (3.23 +/- 1.06). Our data indicate that multiple administration of flunixin did not alter significantly the parent drug and its metabolite concentrations in plasma, however may cause some small changes in pharmacokinetic parameters.     

Effects of continuous rate intravenous infusion of butorphanol on physiologic and outcome variables in horses after celiotomy

A randomized, controlled, blinded clinical trial was performed to determine whether butorphanol administered by continuous rate infusion (CRI) for 24 hours after abdominal surgery would decrease pain and surgical stress responses and improve recovery in horses. Thirty-one horses undergoing exploratory celiotomy for abdominal pain were randomly assigned to receive butorphanol CRI (13 microg/kg/h for 24 hours after surgery; treatment) or isotonic saline (control). All horses received flunixin meglumine (1.1 mg/kg IV q12h). There were no significant differences between treatment and control horses in preoperative or operative variables. Treatment horses had significantly lower plasma cortisol concentration compared with control horses at 2, 8, 12, 24, 36, and 48 hours after surgery. Mean weight loss while hospitalized was significantly less for treatment horses than control horses, whether expressed as total decrease in body weight (13.9+/-3.4 and 27.9+/-4.5 kg, respectively) or as a percentage decrease in body weight (2.6+/-0.7 and 6.3+/-1.1%, respectively). Treatment horses were significantly delayed in time to first passage of feces (median times of 15 and 4 hours, respectively). Treatment horses had significantly improved behavior scores during the first 24 hours after surgery, consistent with the conclusion that they experienced less pain during that time. Butorphanol CRI during the immediate postoperative period significantly decreased plasma cortisol concentrations and improved recovery characteristics in horses undergoing abdominal surgery.     

Equine thyroid function tests: a preliminary investigation.

A similar and significant (P less than 0.001) increase in plasma thyroxine (T4) concentration was seen in seven clinically normal thoroughbred horses 2 h after the intravenous administration of either 2.5 iu or 5 iu of thyroid stimulating hormone (TSH) with a peak response around 4 h after administration. The intravenous administration of 0.2, 0.5 or 1 mg thyrotrophin releasing hormone (TRH) resulted in a significant (P less than 0.01) increase in T4 concentration in three groups of animals; six thoroughbreds in full work, five thoroughbreds at rest and four ponies at rest. The peak response was recorded at 3 or 4 h after administration. A significant difference between the groups in the degree of response to TRH was only found between the thoroughbreds in work and those at rest with 1 mg TRH (P less than 0.05). When two additional ponies were investigated in a similar way, a reduced response to TRH was observed: a pregnant mare had a similar response to 5 iu TSH as the thoroughbreds; the other pony also showed a lowered response to TSH. In a group of 2- or 3-year-old thoroughbreds in training no difference in the T4 response 4 h after intravenous administration of 0.5 mg TRH could be determined, according to the month, age, sex or work intensity. Although resting T4 concentrations did not differ significantly between animals believed to be suffering from the equine rhabdomyolysis syndrome (ERS) and those suffering from a variety of other conditions, some ERS sufferers may have a lowered response to TRH.     

Effects of training on maximum oxygen consumption of ponies

OBJECTIVES: To establish maximum oxygen consumption VO2max) in ponies of different body weights, characterize the effects of training of short duration on VO2max, and compare these effects to those of similarly trained Thoroughbreds. ANIMALS: 5 small ponies, 4 mid-sized ponies, and 6 Thoroughbreds. PROCEDURE: All horses were trained for 4 weeks. Horses were trained every other day for 10 minutes on a 10% incline at a combination of speeds equated with 40, 60, 80, and 100% of VO2max. At the beginning and end of the training program, each horse performed a standard incremental exercise test in which VO2max was determined. Cardiac output (Q), stroke volume (SV), and arteriovenous oxygen content difference (C [a-v] O2) were measured in the 2 groups of ponies but not in the Thoroughbreds. RESULTS: Prior to training, mean VO2max for each group was 82.6 = 2.9, 97.4 +/- 13.2, and 130.6 +/- 10.4 ml/kg/min, respectively. Following training, mean VO2max increased to 92.3 +/- 6.0, 107.8 +/- 12.8, and 142.9 +/- 10.7 ml/kg/min. Improvement in VO2max was significant in all 3 groups. For the 2 groups of ponies, this improvement was mediated by an increase in Q; this variable was not measured in the Thoroughbreds. Body weight decreased significantly in the Thoroughbreds but not in the ponies. CONCLUSIONS AND CLINICAL RELEVANCE: Ponies have a lower VO2max than Thoroughbreds, and larger ponies have a greater VO2max than smaller ponies. Although mass-specific VO2max changed similarly in all groups, response to training may have differed between Thoroughbreds and ponies, because there were different effects on body weight.     

Effect of age and training on murmurs of atrioventricular valvular regurgitation in young thoroughbreds

Cardiac auscultation was carried out on 111 Thoroughbred horses age 2-5 years to test the hypothesis that athletic training might influence the development of atrioventricular (AV) valve regurgitation in young Thoroughbreds. Murmurs of valvular regurgitation were identified and graded on a 1-6 scale. There were 2 sources of auscultation data: 1) 55 2-year-old horses that were examined by auscultation before training commenced and 9 months later when at race fitness; 2) 56 horses age 2-5 years that were examined on one occasion only (25 2-year-olds, 23 3-year-olds, five 4-year-olds and five 5-year olds). All horses in the second data set were in full training and racing regularly at the time of the examination. To conclude the study, 35 horses were selected randomly from both groups of horses and examined with colour-flow Doppler echocardiography. The aim of the final part of the study was to check specificity and sensitivity of auscultation for detection of AV valve murmurs and therefore validate the auscultation findings. Prior to training, the prevalence in 2-year-old racehorses of murmurs of mitral regurgitation and tricuspid regurgitation was 7.3% (4/55) and 12.7% (7/55), respectively. After training, the prevalence proportions increased to 21.8% (12/55) and 25.5% (14/55). After training, one horse developed a murmur characteristic of aortic regurgitation. The differences in murmur prevalence were statistically significant for mitral and tricuspid regurgitation (paired t test results: mitral regurgitation, P = 0.019; tricuspid regurgitation, P = 0.007), as were the differences in mean murmur grade (P = 0.018 and P = 0.0006, respectively). There were no significant effects of age on the prevalence of valvular regurgitation in 56 horses examined at race fitness. Auscultation was a specific (specificity 100%) and reasonably sensitive method for detection of murmurs of mitral and tricuspid regurgitation (mitral regurgitation: positive predictive value 100%, negative predictive value 84%, tricuspid regurgitation: positive predictive value 100%, negative predictive value 65%). These data suggest that the prevalence and grade of murmurs of mitral and tricuspid valvular regurgitation increase in 2-year-old Thoroughbreds after 9 months of athletic training. Whereas the effects of age and growth on the prevalence of murmurs cannot be ruled out from these data, this study suggests that there is an influence of athletic training on the development of atrioventricular valvular regurgitation in flat-racing Thoroughbreds.     

The role of procaine in adverse reactions to procaine penicillin in horses

Procaine penicillin is a commonly used antibiotic in equine medicine but its use is associated with a substantial incidence of adverse reactions. Soluble procaine concentrations were determined by HPLC in several commercially available procaine penicillin preparations, including some that were involved in adverse reactions. The mean (+/- SEM) soluble procaine concentrations in the veterinary preparations was 20.18 +/- 5.07 mg/ml, which was higher than the concentration in the only procaine penicillin preparation for use in humans in Australia of 7.3 mg/ml. Heating the veterinary procaine penicillin preparations to 50 degrees C for 1 day led to a significant (P less than 0.01) increase in the amount of soluble procaine. Heating to 50 degrees C for 7 days also produced a significant (P less than 0.02) increase. Soluble procaine tended to return to baseline concentrations when veterinary procaine penicillin preparations were heated to 50 degrees C for 2 days then stored for 7 days at room temperature. Administration of procaine HCl intravenously (IV) at 2, 5, and 10 mg/kg produced behavioural, locomotor and vascular reactions, which were clinically similar to those reported in adverse reactions to procaine penicillin. The more severe reactions occurred at higher doses, although different horses responded variably at the same dose. Some adverse reactions lead to recumbency but none were fatal. The blood procaine concentrations 1 min after IV administration averaged 19.0 +/- 12.6 and 25.3 +/- 16 micrograms/ml at 2.5 mg/kg and 5 mg/kg, respectively. Ten min after administration, blood procaine concentrations were significantly higher (P less than 0.001) in the 5 mg/kg group than in the 2.5 mg/kg group. Intramuscular (IM) procaine HCl at 5 mg/kg produced significantly lower (P less than 0.001) blood concentrations than similar IV doses, and, in contrast to the IV doses, the amount of procaine in the blood was significantly higher 5 and 10 min after administration than it was after 1 min. Mild excitatory reactions in 4/5 horses were noted 5 to 10 min after IM administration. Administration of diazepam 20 s before procaine HCl prevented the excitatory adverse reaction in 2/2 horses, but administration after the procaine did not influence the outcome.     

Pharmacokinetics of flunixin meglumine in lactating cattle after single and multiple intramuscular and intravenous administrations

The pharmacokinetics of flunixin were studied in 6 adult lactating cattle after administration of single IV and IM doses at 1.1 mg/kg of body weight. A crossover design was used, with route of first administration in each cow determined randomly. Plasma and milk concentrations of total flunixin were determined by use of high-pressure liquid chromatography, using an assay with a lower limit of detection of 50 ng of flunixin/ml. The pharmacokinetics of flunixin were best described by a 2-compartment, open model. After IV administration, mean plasma flunixin concentrations rapidly decreased from initial concentrations of greater than 10 micrograms/ml to nondetectable concentrations at 12 hours after administration. The distribution phase was short (t1/2 alpha, harmonic mean = 0.16 hours) and the elimination phase was more prolonged (t1/2 beta, harmonic mean = 3.14 hours). Mean +/- SD clearance after IV administration was 2.51 +/- 0.96 ml/kg/min. After IM administration, the harmonic mean for the elimination phase (t1/2 beta) was prolonged at 5.20 hours. Bioavailability after IM dosing gave a mean +/- SD (n = 5) of 76.0 +/- 28.0%. Adult, lactating cows (n = 6) were challenge inoculated with endotoxin as a model of acute coliform mastitis. After multiple administration (total of 7 doses; first IV, remainder IM) of 1.1 mg/kg doses of flunixin at 8-hour intervals, plasma flunixin concentrations were approximately 1 microgram/ml at 2 hours after each dosing and 0.5 micrograms/ml just prior to each dosing. Flunixin was not detected in milk at any sampling during the study.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glutathione peroxidase activity in whole blood and plasma of horses of different ages, sexes and different use]

GSH-Px activity in blood and plasma of 269 horses was determined and interrelated to age, sex, and type of use or breed. Furthermore values in blood were related to hematocrit and hemoglobin contents. Trotters and riding horses had higher GSH-Px activities in plasma as well as in blood (0.83 +/- 0.22 and 0.79 +/- 0.23 U/ml plasma or 27.2 +/- 4.3 and 24.0 +/- 7.0 U/ml blood) than Thoroughbreds in training and yearlings (0.61 +/- 0.,14 and 0.56 +/- 0.16 U/ml plasma or 20.6 2 +/- 6.9 and 24.6 +/- 4.3 U/ml blood). 3 to 6 years old Thoroughbreds had higher GSH-Px-activities than 1 to 2 years old ones. Colts and fillies did not have differing values.     

Flunixin pharmacokinetics and serum thromboxane inhibition in the dog

Flunixin meglumine administered orally to beagle dogs at doses of 0.55, 1.10 or 1.65 mg/kg bodyweight was rapidly absorbed to produce maximum mean plasma concentrations of 2.40 +/- 0.70, 4.57 +/- 1.12 and 7.42 +/- 2.07 micrograms/ml, respectively. Thereafter, the plasma concentrations of flunixin fell rapidly to values less than 0.10 micrograms/ml from 24 hours after drug administration at all dosage levels. The maximum mean inhibition of serum thromboxane B2 was 91.5 per cent after the lowest dose of flunixin and 98.8 per cent for both the intermediate and high dose rates. At plasma concentrations of flunixin above 2 micrograms/ml there was more than 90 per cent inhibition of thromboxane.     

The ratio of cardiopulmonary blood volume to stroke volume as an index of cardiac function in horses

A method was developed for determining the ratio of cardiopulmonary blood volume to stroke volume, in horses. The radioisotope 99 Tc (technetium 99m pertechnetate) was injected into the jugular vein as a bolus, which was then detected in the right and left ventricles consecutively by a scanning device consisting of a Na I crystal, a collimator, an amplifier and a discriminator. The radiocardiogram (RCG) and the ECG were recorded simultaneously by a two-channel writing device. The ratio of cardiopulmonary blood volume to stroke volume (cardiopulmonary flow index = CPFI) was then determined from the RCG and ECG tracings. Five categories of horses were examined, viz. Thoroughbreds in training, showjumpers in training, horses not in training, horses with cardiovascular disease and horses with chronic lung disease. The mean CPFI of the above categories were respectively 7.0 +/- 0.39, 7.3 +/- 0.45, 6.7 +/- 0.61, 9.8 +/- 1.30 and 6.2 +/- 0.47. The mean CPFI of the subjects with heart disease was significantly greater than the mean values of the other four categories (P less than 0.001). It was concluded that the CPFI was a reproducible physiological parameter in horses and that the value was significantly increased in our series of subjects with heart disease.     

Comparison of yearling, two-year-old and adult Thoroughbreds using a standardised exercise test

The purpose of this study was to compare exercise measurements in yearling, two-year-old and adult Thoroughbreds using a standardised treadmill incremental exercise test. Peak oxygen consumption (VO2 peak: 128.0 +/- 2.1, 140.0 +/- 2.1, 163.7 +/- 3.4; ml/kg/min +/- se, P less than 0.05), peak packed cell volume (PCV peak: 0.50 +/- 0.01, 0.58 +/- 0.01, 0.64 +/- 0.01 litres/litre +/- se, P less than 0.05) and the maximum number of steps completed in the exercise test (STEPmax: 7.7 +/- 0.1, 8.1 +/- 0.1, 8.6 +/- 0.1; steps +/- se, P less than 0.05) increased with age and degree of physical activity. Peak venous lactate concentration (LACpeak: 21.3 +/- 1.5, 19.5 +/- 1.7, 14.4 +/- 1.7; mmol/litre +/- se, P less than 0.05) and peak respiratory exchange ratio (Rpeak) were significantly higher in both groups of younger horses compared to the adult racehorses. Peak heart rate (HRpeak: 230 +/- 2, 231 +/- 3, 229 +/- 3; beats/min +/- se) did not change with age or training. The rate of change of VO2 between steps in the exercise test (VO2trans) was significantly lower in the adult racehorses at the highest exercise intensities. The slopes of the linear approximation between R (LinR bx), the natural log transformation of venous lactate concentration (LogLAC bx), and heart rate (HR bx) with velocity were significantly lower in the trained adult racehorses. The slope of venous lactate concentration normalised to per cent VO2peak (LogLAC per cent bx) was significantly lower and R breakpoint (R brkpt) normalised to per cent VO2peak was significantly higher in the trained adult racehorses. There was a more rapid decrease in venous lactate and a more rapid return to initial R values in the adult horses relative to the younger, untrained horses. No significant age or training effects were found in the remainder of the post exercise measurements. These results indicate that aerobic power and exercise capacity increased with age and training. Anaerobic power was already well developed even at a young age.