Association of high-speed exercise with racing injury in thoroughbreds

OBJECTIVE

To determine the association between high-speed exercise and risk of injury while racing among Thoroughbreds in Kentucky.

DESIGN

Matched case-control study.

ANIMALS

206 Thoroughbreds that sustained a musculoskeletal injury while racing and 412 Thoroughbreds that were not injured during the same races.

PROCEDURE

Data regarding official timed workouts and races and the Beyer's numbers for the 3 races before the race during which injury occurred were extracted from past performance charts and compared between injured horses and control horses.

RESULTS

For injured horses, cumulative distance of high-speed exercise during the 1- and 2-month periods prior to the race in which injury occurred was significantly less than that of control horses; for either period, a difference of 10 furlongs was associated with approximately 2-fold greater risk of injury. Beyer's numbers were significantly higher for injured horses than for control horses. These effects remained significant after adjusting for age and results of prerace physical inspection.

CONCLUSIONS AND CLINICAL RELEVANCE

In Kentucky, injured horses had significantly less cumulative high-speed exercise than did control horses during the 1- and 2-month periods prior to the race in which injury occurred. These results differ from those observed in California. The association of injury with cumulative high-speed exercise appears to vary among regions in the United States.

Results of physical inspection before races and race-related characteristics and their association with musculoskeletal injuries in Thoroughbreds during races

OBJECTIVE

To estimate the relative risk of injury among horses deemed to be at increased risk of injury on the basis of prerace physical inspection findings and to examine the association of injury during races with race-related characteristics.

DESIGN

Cohort study.

ANIMALS

2,187 Thoroughbred horses that started 3,227 races in Kentucky.

PROCEDURE

All race starts for which a horse was deemed to be at increased risk of injury on the basis of prerace physical inspection findings and a random sample of race starts for which horses were not deemed at increased risk of injury were included in the study. Findings of prerace physical inspection, race-related characteristics, and outcome of the race (race results and whether the horse incurred an injury) were recorded for each race start. Race starts in which a horse incurred an injury during a race were compared with race starts in which injuries were not incurred to identify factors associated with injury during races.

RESULTS

Abnormality of the suspensory ligament of the forelimbs detected during prerace physical inspection, racetrack, class of race (claiming race < or = $25,000 vs other classes), and distance of race (< 7 furlongs vs other distances) were significantly associated with increased risk of injury.

CONCLUSIONS AND CLINICAL RELEVANCE

Prerace physical inspection findings, particularly abnormalities of the suspensory ligament, may be used to identify horses at increased risk of injury during races. Rate of injury differed among racetracks, and horses in certain types of races (lower-priced claiming races and races of shorter distance) may be at increased risk of injury during races.

Frequency of musculoskeletal injuries and risk factors associated with injuries incurred in Quarter Horses during races

OBJECTIVE

To determine the frequency and anatomic location of musculoskeletal injuries incurred by Quarter Horses during races and to compare data from injured horses and matched control horses.

DESIGN

Matched case-control study.

ANIMALS

97 Quarter Horses that sustained a musculoskeletal injury during races and 291 horses from the same races that were not injured.

PROCEDURE

Data examined included racing history, race-entrant characteristics, racing events determined by analysis of videotapes of races, and, when performed, results of prerace physical inspections. Data for injured horses were compared with data for control horses, using conditional logistic regression.

RESULTS

Incidence of a catastrophic injury among Quarter Horses during races was approximately 0.8/1,000 race starts, whereas incidence of musculoskeletal injury during racing was approximately 2.2/1,000 race starts. Odds of musculoskeletal injury were approximately 8 times greater among horses assessed to be at increased risk of injury on the basis of results of prerace physical inspection than for horses not considered to be at increased risk of injury. Evidence was lacking that 2-year-old horses were at increased risk of injury or that sex influenced the risk of injury among Quarter Horses during races.

CONCLUSIONS AND CLINICAL RELEVANCE

Incidence of racing injury among Quarter Horses appears to be lower than that observed among Thoroughbreds. Regulatory veterinarians can identify horses at increased risk of injury on the basis of prerace physical inspection, indicating that these inspections could be used to reduce the risk of injury during races.

Mepivacaine: its pharmacological effects and their relationship to analytical findings in the horse

Mepivacaine is a local anaesthetic drug that is widely used in equine medicine and is classified by the Association of Racing Commissioners International (ARCI) as a Class 2 foreign substance that may cause regulators to impose significant penalties if residues are identified in post-race urine samples. Therefore, an analytical/pharmacological database was developed for this agent and its metabolites. Using an abaxial sesamoid local anaesthetic model, it was determined that the highest no-effect dose (HNED) for its local anaesthetic effect was 2 mg. Using enzyme-linked immunosorbent assay (ELISA) screening, it was determined that subcutaneous (s.c.) administration of the HNED of mepivacaine to eight horses yielded a peak urinary concentration of apparent mepivacaine of 63 ng/mL 2 h after injection. The major identified metabolite recovered from equine urine after dosing with mepivacaine is 3-hydroxymepivacaine. Therefore, 3-hydroxymepivacaine was synthesized, purified and characterized, and a quantitative mass spectrometric method was developed for this metabolite as isolated from horse urine. Following subcutaneous injection of the HNED of mepivacaine, the concentration of 3-hydroxymepivacaine recovered from horse urine reached a peak of about 64.6 ng/mL at 4 h after administration as measured by GC/MS. The concentration of mepivacaine or its metabolites after administration of a HNED dose are detectable by mass spectral techniques. Within the limits of this research, the study suggests that recovery of concentrations less than about 65 ng/mL of 3-hydroxymepivacaine from post-race urine samples may not be associated with a recent LA effect of mepivacaine.

Lidocaine in the horse: its pharmacological effects and their relationship to analytical findings

Lidocaine is a local anaesthetic agent that is widely used in equine medicine. It is also an Association of Racing Commissioners International (ARCI) Class 2 foreign substance that may cause regulators to impose substantial penalties if residues are identified in post race urine samples. Therefore, an analytical/pharmacological database was developed for this drug. Using our abaxial sesamoid local anaesthetic model, the highest no-effect dose (HNED) for the local anaesthetic effect of lidocaine was determined to be 4 mg. Using enzyme-linked immunosorbent assay (ELISA) screening, administration of the HNED of lidocaine to eight horses yielded peak serum and urine concentrations of apparent lidocaine of 0.84 ng/mL at 30 min and 72.8 ng/mL at 60 min after injection, respectively. These concentrations of apparent lidocaine are readily detectable by routine ELISA screening tests (LIDOCAINE ELISA, Neogen, Lexington, KY). ELISA screening does not specifically identify lidocaine or its metabolites, which include 3-hydroxylidocaine, dimethylaniline, 4-hydroxydimethylaniline, monoethylglycinexylidine, 3-hydroxymonoethylglycinexylidine, and glycinexylidine. As 3-hydroxylidocaine is the major metabolite recovered from equine urine, it was synthesized, purified and characterized, and a quantitative mass spectrometric method was developed for 3-hydroxylidocaine as recovered from horse urine. Following subcutaneous (s.c.) injection of the HNED of lidocaine, the concentration of 3-hydroxylidocaine recovered from urine reached a peak of about 315 ng/mL at 1 h after administration. The mean pH of the 1 h post dosing urine samples was 7. 7, and there was no apparent effect of pH on the amount of 3-hydroxylidocaine recovered. Within the context of these experiments, the data suggests that recovery of less than 315 ng/mL of 3-hydroxylidocaine from a post race urine sample is unlikely to be associated with a recent local anaesthetic effect of lidocaine. Therefore these data may be of assistance to industry professionals in evaluating the significance of small concentrations of lidocaine or its metabolites in postrace urine samples. It should be noted that the quantitative data are based on analytical methods developed specifically for this study, and that methods used by other laboratories may yield different recoveries of urine 3-hydroxylidocaine.

Absence of detectable pharmacological effects after oral administration of isoxsuprine

Isoxsuprine is reported to be a peripheral vasodilator used in human and veterinary medicine to treat ischaemic vascular disease. In horses, it is generally administered orally to treat navicular disease and other lower limb problems. To define the scope and duration of its pharmacological responses after oral administration, 6 horses were dosed with isoxsuprine HCl (1.2 mg/kg bwt) q. 12 h for 8 days and then tested to assess the duration and extent of pharmacological actions. There was no significant difference between isoxsuprine and control treatment values for heart rate, spontaneous activity, sweat production, anal muscle tone, core and skin temperatures, and cutaneous blood flow. The lack of pharmacological effect following oral administration was in sharp contrast to the marked response following i.v. dosing reported in earlier experiments.

Development and characterization of an equine behaviour chamber and the effects of amitraz and detomidine on spontaneous locomotor activity

This report describes the development of a behaviour chamber and the validation of the chamber of measure locomotor activity of a horse. Locomotor activity was detected by four Mini-beam sensors and recorded on a data logger every 5 min for 22 h. Horses were more active during daytime than in the evening, which was at least partially related to human activity in their surroundings. To validate the ability of the chambers to detect changes in activity, fentanyl citrate and xylazine HCl, agents well-characterized as a stimulant and a depressant, respectively, were administered to five horses. Fentanyl citrate (0.016 mg/kg) significantly increased locomotor activity which persisted for 30 min. Xylazine HCl (1 mg/kg) significantly reduced locomotor activity for 90 min. Amitraz produced a dose-dependent decrease in locomotor activity, lasting 75 min for the 0.05 mg/kg dose, 120 min for the 0.10 mg/kg dose, and 180 min for the 0.15 mg/kg dose. In a separate experiment, yohimbine administration immediately reversed the sedative effect of amitraz. This suggests there is a similarity in the mode of action of amitraz, xylazine and detomidine, as yohimbine acts primarily by blocking central alpha 2 -adrenoceptors that are stimulated by agents like xylazine. There was also a significant decrease in locomotor activity following injection of detomidine (0.02, 0.04 and 0.08 mg/kg) for 1.5, 3.5 and 5.0 h, respectively. The locomotor chamber is a useful, sensitive and highly reproducible tool for measuring spontaneous locomotor activity in the horse, which allows investigators to determine an agent's average time of onset, duration and intensity of effect on movement.

Racing-related factors and results of prerace physical inspection and their association with musculoskeletal injuries incurred in thoroughbreds during races

OBJECTIVE

To describe and compare data from Thoroughbreds that sustained musculoskeletal injuries while racing with data from matched control horses.

DESIGN

Matched case-control study.

ANIMALS

216 Thoroughbreds that sustained a musculoskeletal injury while racing and 532 horses from the same races that were not injured.

PROCEDURE

Data regarding racing history, race-entrant characteristics, racing events determined by analysis of videotapes of races, and results of prerace physical inspections were determined for all horses. Injured horses were compared with control horses by using conditional logistic regression.

RESULTS

Results of prerace inspection by regulatory veterinarians were significantly associated with injury. Odds of musculoskeletal injury, injury of the suspensory apparatus of the forelimb, and injury of the tendon of the superficial digital flexor muscle of the forelimb were 5.5 to 13.5 times greater among horses assessed to be at increased risk of injury by regulatory veterinarians on the basis of results of prerace inspection than for horses not considered to be at increased risk of injury. Odds of an abnormal finding in the suspensory ligament during prerace inspection were 3.4 times greater among horses that injured the suspensory apparatus than among control horses, and odds of an abnormal finding in the tendon of the superficial digital flexor muscle during prerace inspection were 15 times greater among horses that injured the tendon than among control horses.

CLINICAL IMPLICATIONS

Regulatory veterinarians can identify horses during prerace physical inspection that have an increased risk of injury during races. Prerace physical inspections could be used to reduce the risk of injury to Thoroughbreds during races.

Lack of local anaesthetic efficacy of Sarapin in the abaxial sesamoid block model

Sarapin is a distillate of the pitcher plant that has long been used in human and veterinary medicine for 'regional analgesia'. The mechanism of the reported analgesic response is unknown; however, the agent is purported to provide more effective analgesia for slow, chronic pain than for sharp, acute pain. Reportedly, Sarapin is also widely used as an analgesic agent in the horse, generally in combination with corticosteroids and other agents. To determine its local anaesthetic efficacy in the horse, we tested Sarapin in a unilateral abaxial sesamoid block model at two dose levels, 2 mL and 10 mL per site, respectively. Cutaneous pain was induced with a light/heat lamp, and analgesia was assessed by measuring the hoof-withdrawal reflex latency period. Neither dose of Sarapin altered hoof-withdrawal reflex latency in this experimental model tested over a two-week period. Based on the demonstrated efficacy of this local anaesthetic model, it seems clear that Sarapin has no significant classical local anaesthetic actions in the horse, and probably not in other species either.

Character and duration of pharmacological effects of intravenous isoxsuprine

Isoxsuprine is a therapeutic medication used to treat navicular disease and other lower limb problems in horses and is one of the more frequently detected therapeutic agents in racing horses. In a crossover study, horses were administered isoxsuprine i.v. to determine the character and duration of its pharmacological effects. Isoxsuprine significantly increased heart rate 5-150 min following injection. Unrestrained activity following isoxsuprine treatment was significantly greater than control activity for 105 min after treatment. There was an apparent, although statistically nonsignificant, increased cutaneous blood flow resulting in visible water vapour and sweat production 5-60 min after administration. Initially, there was no difference in skin temperature between control and isoxsuprine treatment values; however, skin temperature decreased below control values 45-120 min after injection. Concurrently, there was a significant decrease in rectal temperature reflecting a decrease in body core temperature. Using infrared thermography, a significant decrease in superficial skin temperature of the front legs occurred 30-240 min after treatment. Isoxsuprine also reduced smooth muscle tone, which was apparent by decreased tone of the internal anal sphincter 10-180 min after treatment. It was concluded that the measurable pharmacological effects of i.v. isoxsuprine are short lived, since none of the above responses were apparent 4 h or more after i.v. administration.

Regulatory significance of procaine residues in plasma and urine samples: preliminary communication

Plasma and urinary concentrations of procaine and the duration of response to procaine after its administration as a local anaesthetic to horses were studied. Following injection of a clinical dose of procaine HCl (80 mg), the concentration of procaine in plasma was less than the lower limit of quantitation and unsuitable for threshold determination. Therefore, the urinary concentration of procaine was determined after injection of a dose of 5 mg procaine HCl, the highest no-effect dose (HNED) of this agent. Free unconjugated procaine in equine urine reached a peak concentration of 23.7 ng/mL, while total (unconjugated plus conjugated) procaine peaked at 37.9 ng/mL (mean urine pH of 8.5). Because a basic drug may concentrate substantially in acidic urine, a threshold concentration of 25 ng/mL of unconjugated procaine is a reasonable and conservative threshold for procaine at this time. Horses were administered abaxial sesamoid blocks containing 2% procaine HCl (40, 80, 160 and 320 mg) and 2% procaine HCl (40 and 320 mg) with epinephrine (1:100,000) in local anaesthetic experiments. There was a significant local anaesthetic (LA) effect for all doses of procaine HCl with the duration of effect ranging from 30 min (40 mg) to 60 min (320 mg). The addition of epinephrine significantly increased the duration of local anaesthesia to 180 min for a 40 mg dose and 420 min for a 320 mg dose. Because epinephrine may extend the duration of local anaesthesia beyond a reasonable period of confinement for horses before the starting time of a race, the increased LA effect following the addition of epinephrine to procaine has regulatory significance.

Determination of highest no effect dose (HNED) for local anaesthetic responses to procaine, cocaine, bupivacaine and benzocaine

The highest no effect doses (HNEDs) for the local anaesthetic (LA) effects of procaine, cocaine, bupivacaine and benzocaine were determined using the heat lamp/hoof withdrawal model of Kamerling et al. (1985b) and the abaxial sesamoid block model of local anaesthesia. The heat lamp rapidly (4 or 5 s) increased the temperature of the superficial skin layers of the pastern to about 90 degrees C, at which point the animal sharply withdrew its hoof. Effective LA blockade precluded this response and superficial skin temperatures exceeded 120 degrees C. Thermal stimulus experiments were routinely terminated after 10 s of exposure to prevent undue tissue damage. Following abaxial sesamoid block with bupivacaine, the HNED for that drug was about 0.25 mg/site. Increasing the dose to 2 mg/site apparently produced complete and prolonged LA blockade. Analogous work showed that the HNED for procaine was about 2.5 mg/site. Similarly, the dose response curve for procaine was parallel with that of bupivacaine but was shifted 10-fold to the right. The duration of the LA response following procaine injection was less than for bupivacaine with the statistically significant response following 40 mg/site injection lasting less than 45 min. Cocaine was less potent than procaine, showing a shallower dose response curve. The HNED for cocaine was less than 5 mg/site, although at this dose the duration of action was extremely short (< 7.5 min). Benzocaine had no significant LA action when a dose of 800 mg was applied topically as a 5% preparation. These results show that the HNEDs for bupivacaine and procaine are remarkably low, that cocaine is somewhat less potent as a LA than might be expected, and that 5% topical benzocaine has no significant pharmacology. The small doses of bupivacaine and procaine producing effective local anaesthesia suggests that developing plasma thresholds for these agents is likely to be very challenging.

Disability syndrome: the effects of early vs delayed rehabilitation intervention

1. Disability syndrome occurs when an individual with a work related injury or other disability chooses not to work when it has been medically determined that they are capable of doing so. 2. A possible contributor to the development of disability syndrome includes systems reinforcers or rules that discourage return to work. For example, many attorneys discourage early return to work or modified duty. 3. Early intervention by rehabilitation counselors at the time of injury can facilitate a positive attitude and empower the worker to resist the negative effect of systems reinforcers that discourage early return to work.

Prevalence of, and factors associated with, musculoskeletal racing injuries of thoroughbreds

All horses diagnosed by a commission veterinarian of the Kentucky Racing Commission as having sustained a musculoskeletal injury, defined as an obvious change in soundness immediately before, during, or after a race held between Jan 1, 1992 and May 31, 1993 were included in a study to determine the prevalence of and factors associated with racing injuries involving the musculoskeletal system of horses competing at 4 Thoroughbred racetracks in Kentucky. During the 17-month study, there were 35,484 racing starts among 7,649 horses in 3,824 official Kentucky Racing Commission races. During this period, 132 musculoskeletal racing injuries were diagnosed among 117 horses. Twenty-eight injured horses were male, 46 were geldings, and 43 were female. The prevalence of horses with racing injuries per racing start was 0.33% (117/35,484). The injuries of 51 horses were classified as catastrophic, and 66 as noncatastrophic. The prevalence of horses with catastrophic injuries per racing start was 0.14% (51/35,484). The proportion of horses with injuries of the left forelimb, sesamoid, and third metacarpal bone in the catastrophic group was significantly (P < or = 0.05) greater than those of horses in the noncatastrophic group. The proportion of horses with injuries of the superficial digital flexor tendon among those in the catastrophic group was significantly less than that of horses in the noncatastrophic group. The distance of the race was significantly shorter and the number of turns less among horses with catastrophic injuries than among horses with noncatastrophic injuries.(ABSTRACT TRUNCATED AT 250 WORDS)