Track condition and racing injuries in thoroughbred horses

The incidences of fractures and soft tissue injuries during 68397 starts of thoroughbred horses at New York Racing Association tracks were analyzed concerning track condition, dirt and turf tracks, environmental conditions, length of races, location of fractures on the track, and age of horses. It was concluded that the conditions evaluated are of no importance in the occurrence of racing injuries to thoroughbred horses.     

Heritability of racing performance in thoroughbred horses

The héritabilitý of performance in thoroughbreds was studied using the Timeform Ratings for horses which raced during 1970. Timeform Ratings are based on the relative performance of all horses racing in a given year. 794 Individual three year old records, representing 96 sires which had five or more progeny, were used.The mean ratings for sires, dams and progeny were 128.5, 93.6 and 81.4 respectively; among the progeny the ratings for colts, fillies and geldings were 88.3, 79.1 and 77.1 respectively. Calculations made suggest that while stallion selection is effective in selecting sires with high performance ratings it does not appear that the selection of dams is very closely related to performance. There was no evidence of assortative mating.Paternal half sib and regression of offspring on sire analyses of the data yielded heritability estimates of 0.35 ± 0.11 and 0.74 ± 0.20 respectively. Further regression analyses on a reduced set of data (553 progeny records) of offspring on sire, offspring on dam and offspring on mid parent value gave heritabilities 0.56 ± 0.20, 0.36 ± 0.10 and 0.34 ± 0.08respectively. The possible reason for the substantially higher heritability estimates from the regressions of offspring on sire are discussed. It is concluded that the best measure of heritability of performance is 35%.     

Risk factors associated with injuries in thoroughbred horses.

A case-control study was conducted on Thoroughbred horses to identify factors associated with the risk of breakdown on racetracks. A total of 310 cases (breakdowns) were identified from the Horse Identification Department records kept by the chief examining veterinarian of New York Racing Association. For each case, two control horses were selected randomly from the Daily Racing Form Inc. records. Multiple logistic regression analysis was used to identify and quantify the risk of factors associated with breakdown, while simultaneously controlling for the effect of other putative factors. Factors associated with risk of breakdown were: track (horses raced on Saratoga racetrack were at a lesser risk of breakdown), track composition/condition (turf tracks had a lower risk compared to dirt), number of seasons in race, racing in a later race, number of starts per year, the total number of starts, season (summer had a higher risk than winter or spring) and age of the horse.     

Genetic parameters of racing merit of thoroughbred horses in Poland

The study aimed at estimating variance components of racing ability traits in thoroughbred horses as a contribution to defining the breeding objective for this breed. Data collected were 12 143 placings at finish (square root) and 8641 earnings (log) won by 1414 horses running in 1693 races over the period of 1998–2001. Age of horses ranged from 2 to 5+ years, and the distances were from 1000 to 3200 m. Horses were from 11 state stables, from private breeders (one collective group), and from foreign breeding (another collective group within the factor ‘breeder’). Variance components were estimated by the residual maximal likelihood (REML) method. Statistical analysis accounted for fixed effects of year, age, race, breeder (optional), sex, weight carried and distance, and for the random effects of rider, permanent environment, and animal additive genetics. Pedigrees were at least three generations deep. When breeder effect was excluded from the model, heritability coefficients were 0.12 and 0.18, repeatability 0.23 and 0.34 for earnings and placings at finish, respectively.     

Values of urine specific gravity for thoroughbred horses treated with furosemide prior to racing compared with untreated horses.

The distribution of specific gravity values for 2,599 urine samples collected from racing Thoroughbred horses that were known to have received furosemide prior to racing was compared with that for 1,669 urine samples from racing Thoroughbred horses that reportedly had not received furosemide. Values of specific gravity for furosemide-treated horses were significantly lower (P < 0.001) than those for horses that had not received furosemide, and the proportion of horses with urine specific gravity either <1.010 or <1.012 was significantly greater (P < 0.001) among the furosemide-treated horses. These data indicate that evaluation of urine specific gravity would be a useful component of drug testing programs for regulation of furosemide use.     

Metabolic response to racing and fiber properties of skeletal muscle in standardbred and thoroughbred horses

Muscle biopsies were obtained from 17 Standardbred trotters (S) and 22 Thoroughbred racehorses (T) after races which varied in length from 1200 to 2840 m. Biopsies were taken between 2 and 14 minutes from the conclusion of the race. Histochemical and biochemical analyses were performed on all muscle samples. Standardbred horses possessed fewer Type II fibers, especially Type IIB fibers, and demonstrated a higher oxidative and lower glycolytic capacity in muscle than Thoroughbred horses. Intramuscular glycogen and lac-tate concentrations were lower in Standardbred horses after racing (mean 420 and 82 mmol/kg d.w. respectively) com-pared to Thoroughbred horses (mean 545 and 148 mmol/kg d.w. respectively). Low levels of intramuscular adenosine triphosphate (ATP) (mean S 17, T 15 mmol/kg d.w.) and creatine phosphate (mean S 28, T 42 mmol/kg d.w.) were recorded in both breeds after racing. Differences in muscle enzyme activities and metabolic response to exercise between breeds were related to the different muscle fiber compositions of Standardbred and Thoroughbred horses. Within both breeds, a high percentage of Type IIB fibers was associated with a low oxidative and high glycolytic capacity in muscle and a greater lactate accumulation after racing. In Standardbred horses low intramuscular ATP concentrations post-race were associated with a high percentage of Type IIB fibers and high lactate levels. No relationship was found between placing or speed of racing and intramuscular lactate and ATP concentrations post-race. This may have been due to many other factors which affected the outcome of a race and also due to the fact that it was not known when during a race lactate accumulation and ATP depletion occurred. Since the properties of fiber types appeared to be very different, the metabolic response within individual fiber types may be more closely related to fatigue than the metabolic response measured in whole muscle.     

Pharmacokinetics of procaterol in thoroughbred horses

Procaterol (PCR) is a beta‐2‐adrenergic bronchodilator widely used in Japanese racehorses for treating lower respiratory disease. The pharmacokinetics of PCR following single intravenous (0.5 μg/kg) and oral (2.0 μg/kg) administrations were investigated in six thoroughbred horses. Plasma and urine concentrations of PCR were measured using liquid chromatography–mass spectrometry. Plasma PCR concentration following intravenous administration showed a biphasic elimination pattern. The systemic clearance was 0.47 ± 0.16 L/h/kg, the steady‐state volume of the distribution was 1.21 ± 0.23 L/kg, and the elimination half‐life was 2.85 ± 1.35 h. Heart rate rapidly increased after intravenous administration and gradually decreased thereafter. A strong correlation between heart rate and plasma concentration of PCR was observed. Plasma concentrations of PCR after oral administration were not quantifiable in all horses. Urine concentrations of PCR following intravenous and oral administrations were quantified in all horses until 32 h after administration. Urine PCR concentrations were not significantly different on and after 24 h between intravenous and oral administrations. These results suggest that the bioavailability of orally administrated PCR in horses is very poor, and the drug was eliminated from the body slowly based on urinary concentrations. This report is the first study to demonstrate the pharmacokinetic character of PCR in thoroughbred horses.     

Gastric ulceration in mature thoroughbred horses

Routine post mortem examination of 195 Thoroughbreds in Hong Kong revealed that 66 per cent suffered from gastric ulceration. Racehorses killed straight out of training suffered a significantly greater incidence of ulceration (80 per cent) than those having been retired for a month or more (52 per cent). The macroscopic findings post mortem enabled a classification of equine gastric ulceration to be suggested (Types 1, 2, 3), according to severity. Severe lesions (Types 2 and 3) were present in 45 per cent of horses put down from training and 5 per cent of retired horses. This difference was significant. Lesions appeared to be chronically progressive during training, but to regress during retirement. The observed difference of gastric ulceration between the two groups of horses was similar for different age groups.     

Japanese encephalitis in a racing thoroughbred gelding in Hong Kong

A horse in Hong Kong that had been vaccinated against Japanese encephalitis suffered a pyrexic episode that culminated in a hyperexcitable state and self-inflicted trauma. Japanese encephalitis was diagnosed on the basis of clinical, pathological and serological observations, and confirmed by the detection of genomic sequences of the virus in spinal cord tissue. Phylogenetic analyses of E gene and NS5-3'UTR sequences revealed divergent clustering of these segments with previously described genotypes, suggesting the possibility that the horse might have been infected with a recombinant between genotype I and genotype II viruses. Horses are considered to be dead-end hosts for the disease, but the occurrence of an infected horse in a population may have implications for the health status of the national herd. The effect that this case had on the horse industry in Hong Kong is discussed with specific reference to the movement of horses and the vaccination programme for Japanese encephalitis.     

Surgical colic in racing endurance horses

A retrospective study was performed of horses that developed colic during endurance racing, and subsequently required surgery. Fifteen horses met the inclusion criteria, of which 13 (87%) had small intestinal volvulus. Nine of the 15 horses (60%) had a small intestinal resection and anastomosis performed. Post operative ileus, particularly in those horses that had a resection performed, was a common complication. Eleven of the 15 (73%) survived, and 4 (27%) have since raced.     

Pulmonary haemorrhage in standardbred horses after racing

SUMMARY Endoscopic examinations of the upper respiratory tract were done on 92 of 314 Standardbred horses that raced one or more times at 4 consecutive, weekly race meetings. Although participation was voluntary, the characteristics of the population of horses examined were not statistically different from those of all horses that raced. No horse showed epistaxis, but 34 (32.4%) examinations of the trachea revealed blood that ranged from a trace in the tracheal mucus to large amounts scattered over the tracheal walls. Forty-four horses exhibited minor degrees of pharyngeal lymphoid hyperplasia, 2 had asynchronous movement of the left arytenoid cartilage and 15 had grains of sand in the respiratory tract. There was no association between bleeding and age, sex, distance of race, place in race or date of race. Mucus and mucopurulent material occurred less often after longer races and more often on the last 3 race nights.