Nonsteroidal anti-inflammatory agents and musculoskeletal injuries in Thoroughbred racehorses in Kentucky

Catastrophic musculoskeletal injuries in Thoroughbred racehorses in Uruguay, 2011-2017

Catastrophic musculoskeletal injuries (CMI) pose a major welfare concern to horses and their riders, yet limited data is available describing their occurrence in South America. Using a retrospective cohort and case-control design, the objective of the study was to determine the incidence of CMI for Thoroughbreds in training and racing, and associated horse-level risk factors in Uruguay. Seventy-seven Thoroughbreds sustained a CMI; 37 of which were age- and sex-matched to 111 control horses in the same race. Training and racing data from 2011-2017 were collected. Incidence of race day CMI per 1000 race starts and training CMI incidence per 100 horse months were calculated using Poisson regression. Univariable logistic regression was used to assess relationships between race history and occurrence of CMI by fracture location, and multivariably for all fracture locations. Overall race day incidence of CMI was 0.42 per 1000 race starts (95% CI 0.29, 0.60). The incidence of CMI in training was 0.059 per 100 horse months. Most fractures were of the forelimbs (80.3%). There were 32 (41.5%) distal and 39 (50.6%) proximal limb fractures. The risk of CMI was greater for horses with fewer places (P = 0.001), and greater time between the previous race and the race in which CMI occurred (P = 0.020). The rate of race day CMI was low, despite Uruguay being a racing jurisdiction with policies and risk factors associated with higher CMI rates compared to other jurisdictions. Lightly raced horses with long periods since their previous race start should be monitored closely.

Pharmacokinetic Profiles of Metamizole Metabolites after Intramuscular and Intravenous Administration in Healthy Arabian Horses

Metamizole sodium (MT) is an analgesic and antipyretic drug molecule used in humans, horses, cattle, swine, and dogs. Metamizole rapidly hydrolyzes and turns into methylamino antipyrine (MAA), an active primary metabolite of MT. The present study aims to determine the pharmacokinetic (PK) profiles of MT metabolites after intravenous (IV) and intramuscular (IM) administration into sex of Arabian horses (Equus ferus caballus) using a cross-over study design. The plasma samples were extracted by solid-phase extraction (SPE) method, and plasma concentrations of MT metabolites were analyzed by high-performance liquid chromatography (HPLC). After administrations of MT, plasma concentrations of methylamino antipyrine (MAA), amino antipyrone (AA), and acetylamino antipyrone (AAA) were determined within range of 15 min-12 h. Plasma concentrations of AA and AAA were lower than the plasma concentrations of major metabolite MAA at each sampling point. The PK parameters were statistically evaluated for MT's metabolites between male and female horses and also between IM and IV administrations of PK parameters such as C_max , t_max , t_1/2λz , AUC_0-t , AUC_0-∞ , λz, Cl and V_ss (p < .05). The AUC_IM /AUC_IV ratio in female and male horses for MAA was 1.19 and 1.13, respectively. The AUC_IM /AUC_IV ratio for AA was lower than those found for MAA. AUC_IM /AUC_IV ratio was statistically significantly different between male and female horses for AA (p < .05). According to these results, some PK parameters such as Cmax, AUC, and MRT, MAA and AA concentrations have shown statistically significant differences by MT administrations.

Association between the administration of phenylbutazone prior to racing and musculoskeletal and fatal injuries in Thoroughbred racehorses in Argentina

OBJECTIVE

To examine the association between prerace administration of phenylbutazone and the risk of musculoskeletal injury (MSI) and fatal injury in Thoroughbred racehorses that raced between 2006 and 2015 at 2 of the 4 official racetracks in Argentina.

SAMPLE

Data from racetrack databases and veterinary reports on 283,193 race starts.

PROCEDURES

Data were collected relating to race performance and injury outcomes for starts at these tracks. The incidence of MSI and fatal injury was calculated for each year, stratified by the declared prerace administration of phenylbutazone. Univariable logistic regression, followed by multivariable logistic regression, was used to identify significant risk factors for both MSI and fatal injury.

RESULTS

Analyses identified associations between the declared prerace administration of phenylbutazone and the risk of MSI and fatal injury during racing. Horses with declared prerace phenylbutazone administration had greater odds of MSI (OR, 1.45 [95% CI, 1.03 to 2.04]) and fatal injury (OR, 1.59 [95% CI, 1.1 to 2.27]) than did horses racing without prerace phenylbutazone administration. These associations remained significant when other risk factors were accounted for in both multivariable models.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested an association between the prerace administration of phenylbutazone and the risk of MSI and fatal injury in Thoroughbred racehorses during racing. Although these results did not imply a direct causal relationship between prerace phenylbutazone administration and injury, they may be considered in the development of more conservative medication policies to optimize racehorse welfare in North and Latin America.

Characteristics of complete tibial fractures in California racehorses

BACKGROUND

Tibial fractures cause ~3% of racehorse deaths. Pre-existing stress fractures have been associated with multiple racing and training fractures, but not complete tibial fractures.

OBJECTIVES

To describe racehorse tibial fractures and compare signalment and exercise histories of affected and control racehorses.

STUDY DESIGN

Retrospective analysis of necropsy reports.

METHODS

Racehorses that had a complete tibial fracture (1990-2018) were retrospectively reviewed. Signalment and exercise histories of affected horses were compared to 1) racehorses that died because of non-tibial musculoskeletal injuries or 2) non-musculoskeletal cause and 3) age, sex, event-matched control racehorses. Tibial fracture prevalence was described relative to California racehorses that had at least one official work or race. Age, sex and limb distributions were compared between affected and control horses (Chi-square, Fisher's Exact test). Exercise history data were reduced to counts and rates of official high speed works, races and layups (periods without an official high speed work or race >60 days). Variables were compared among groups using matched logistic regression (P ≤ .05).

RESULTS

Tibial fractures in 115 horses (97% unilateral; 50% left, 47% right) occurred most commonly during training (68%) and in 2- to 3-year-old horses (73%). Fractures were predominantly comminuted (93%), diaphyseal (44%) and oblique (40%). Of 61 cases examined for callus, 64% had periosteal callus associated with fracture, most commonly in proximal (65%) and distal diaphyseal (27%) locations. Of 28 racehorses with known exercise history, 57% never raced and 36% had a layup. Affected horses had fewer official-timed works and events (official high speed works and races), number of active days and accumulated less distance in events and works (P < .05) than control horses.

MAIN LIMITATIONS

Retrospective review of necropsy reports by multiple pathologists over 28 years.

CONCLUSIONS

Tibial fractures were associated with pre-existing stress fracture early in career. Most fractures were associated with proximolateral stress fractures.

Meta-analysis of risk factors for racehorse catastrophic musculoskeletal injury in flat racing

Studies of racehorse injury or fatality in various countries have identified common, and in some cases conflicting, risk factors. We conducted a systematic search of the relevant literature published from 1990 to 2017. Peer-reviewed articles were included if they reported the incidence of fatal or catastrophic musculoskeletal injury (CMI) in Thoroughbred flat races (n=21) or risk factors for CMI (n=65). Pooled effect sizes were estimated using the random-effects DerSimonian-Laird model. The pooled incidence of CMI was 1.17 (95% confidence interval 0.90, 1.44) per 1000 race starts. Almost 300 factors have been investigated in epidemiological studies for potential associations with CMI. Factors found to have consistent evidence of increasing risk of CMI are: (1) Horse-level factors such as older horse age and age at first start, male sex, and higher race class or lower claiming price; (2) Race-level factors such as firmer track conditions on turf and wetter conditions on dirt, longer race distance, and a greater number of starters; and (3) Management-related factors including more time since previous start, greater number of starts, longer career length, issues identified at pre-race examination, previous injury, and recent administration of medication or injections. Studies investigating recent cumulative distance of high-speed exercise were conflicting and suggestive of at least two mechanisms of injury related to the accumulation of bone damage: (1) In well adapted bone following a period of intense training; and (2) In poorly adapted bone at relatively low levels of training intensity. Future studies should evaluate success of interventions and mechanisms for injury.

Relationship Between Historical Lameness, Medication Usage, Surgery, and Exercise With Catastrophic Musculoskeletal Injury in Racehorses

Background: The rate of catastrophic musculoskeletal injuries (CMI) in racehorses is high in the United States compared to other countries. Few modifiable risk factors related to lameness, medication, and surgery history have been identified.

Objective: To detect management factors that increase risk of CMI by comparing medical histories between horses that sustained, and horses that did not sustain, a CMI.

Study design: Case-control.

Methods: Racehorse necropsy data (May 2012-June 2013) were obtained through the California Horse Racing Board Postmortem Program. Attending veterinarians of Thoroughbreds (TB) and Quarter Horses (QH) that experienced CMI, and of three matched control horses, were invited to complete an online veterinary medical history survey. We investigated associations between CMI and lameness, medication, surgery, and exercise history using multivariable logistic regression.

Results: There were 146 TB (45 cases, 101 controls) and 17 QH (11 cases, 6 controls) surveys completed. TB cases were more likely to show signs of lameness within the 3 months prior to death compared to controls. A high proportion of both cases (64.3%) and controls (76.8%) were administered medications, but unraced TB case horses were more likely to have been administered systemic medications compared to those that previously raced. TB cases were more likely to have raced with greater intensity during their career, but had eased off in the month preceding CMI. For QHs, there was insufficient power to detect significant differences between cases and controls that showed signs of lameness, or that were administered medications. Surgery history was not associated with CMI.

Main limitation: Insufficient power to detect small effect sizes.

Conclusions: The study provides information that can be used to aid in identification of horses at high risk for catastrophic injury, and management factors that can be modified to reduce the risk for all horses.

A review of objective assessments of orthopaedic analgesic efficacy of non-steroidal anti-inflammatory drugs in horses

There are a limited number of published objective assessments of the orthopaedic efficacy of various non-steroidal anti-inflammatory drugs (NSAIDs) in horses. Several different models of pain in horses have been used, but the least invasive orthopaedic model is the reversible foot lameness model using a shoe with either a mechanical heart bar or an eccentrically-placed threaded nut accommodating a bolt, with both models allowing variable levels of lameness after tightening of the bar or bolt against the solar surface of the foot. These and other models have yielded objective data, reviewed here, on NSAID efficacy in orthopaedic conditions. Phenylbutazone and flunixin are of comparable efficacy, and each is superior to ketoprofen, in the reversible model of foot pain, evidenced at rest, during treadmill exercise, and during recovery after exercise. The selective cyclooxygenase (COX)-2 inhibitor firocoxib, given either orally or intravenously, appears to be an effective alternative to traditional pan-COX-inhibiting NSAIDs, but an initial three-fold loading dose is necessary with intravenous firocoxib to achieve steady state and full efficacy faster than the label dose allows. Meloxicam has also been shown to be effective in two published orthopaedic studies. Acetaminophen/paracetamol has shown some initial promise in preliminary studies using the reversible model of foot pain. Combination therapy should involve appropriately-dosed NSAIDs with differing onsets and durations, whereas drugs with similar onsets and durations may not be synergistic. Sanctioning bodies and local or federal laws may restrict or prohibit the use of NSAIDs before or during equestrian competition.

Epidemiology of Musculoskeletal Injury during Racing on New Zealand Racetracks 2005-2011

The objective of the study was to determine the incidence of veterinary events that resulted in a horse failing to finish a race and identify risk factors for musculoskeletal injury (MSI) during a race. Data were obtained on Thoroughbred flat race starts in New Zealand between 1 August 2005 and 31 July 2011 (six racing seasons). Stipendiary Steward's reports were key-word searched to identify veterinary events that prevented a horse from finishing a race. Race data were used calculate the incidence of veterinary events per 1000 horse starts and Poisson regression was used to investigate risk factors for MSI. There were 188,616 race starts and 177 reported veterinary events. The incidence of MSI on race day was 0.72 per 1000 starts, whilst the incidence of respiratory events was 0.21 per 1000 starts. The rate of MSI was significantly lower on 'dead' and 'slow' tracks compared with 'good' tracks and significantly greater in longer races (≥1671 m) compared with races of ≤1200 m. The rate of MSI during flat races in New Zealand appears lower than that reported worldwide, which may be due to the management and training of horses in New Zealand or differences in case definitions used in comparable studies.