In racing circles, pinhooking is a term used to describe the practice of buying a horse specifically for resale and profit. Pinhooked yearling Thoroughbreds are purchased at public auctions from July through September for the purpose of selling them the following year (February through April) at what are known as 2-year-olds in training sales. Trainers have approximately 5 months to break, condition, and prepare their horses to work at high speed during training in preparation for the sales. At the sales, the trained 2-year-old horses race 1 or 2 furlongs (one-eighth or one-quarter mile). Among the 2-year-olds in training sales that are in a given year, the earlier sales (eg, sales in February) are considered the most important because the mean sale price is higher, compared with that of later sales. After purchase, the horses start racing as 2 year olds.
Knowledge regarding the relationship between lameness and athletic performance in yearling horses in the United States is limited. A previous study1 conducted at a training center in Florida revealed that lameness was the most important cause of training failure in yearling horses, as measured by the number of days on which training could not be performed. In horses affected with lameness, training failure during high-speed exercise in preparation for 2-year-olds in training sales was considered severe (eg, 13 to 108 days of training lost). Financial returns for horses with severe training failure were significantly lower than returns for horses with mild training failure (eg, 1 to 11 days of training lost). In that study,1 however, the anatomic location, diagnosis, and treatment of lameness were not characterized. The purpose of the study reported here was to characterize lameness during training and compare exercise variables and financial returns among yearling Thoroughbreds that were bought for the purpose of resale for profit (ie, pin-hooked horses). On the basis of the racing completed at 2-year-olds in training sales, the performance speed of the horses in the study population was classified as fast, average, or slow, and variables were compared among these 3 groups.
Materials and Methods
Horses—Forty Thoroughbreds (age range, 14 to 21 months) purchased from July through September 2004 for resale at 2-year-olds in training sales (February through April 2005) were included in the study. All 40 horses were from 1 training center in Ocala, Fla. This center was selected because of the number of horses trained and willingness of the trainer to participate. On arrival, horses were vaccinated by the attending veterinarian against equine herpesvirus types 1 and 4, influenza virus types A1 and A2, West Nile virus, eastern and western equine encephalomyelitis viruses, and Clostridium tetani. In addition, horses were vaccinated against Streptococcus equi 3 separate times (October 2004, February 2005, and April 2005).
Training procedures—All horses were broken to ride and underwent the same training program starting October 2004. Briefly, all horses were trotted to the racetrack, fast galloped (22 s/furlong) for a distance of 1.5 miles, and walked back to their stalls 6 days each week; 1 day each week was a rest day. In December, horses were introduced to high-speed exercise (breezing [ie, running at racing speed during training] for 1 or 2 furlongs, typically at a speed ≤ 14 s/furlong) 1 day each week (Saturday), followed by 1 day of rest (Sunday). Horses galloped (at speeds of approx 18 to 22 s/ furlong) on 5 days each week.
Diagnosis of lameness—During training, horses were examined daily for signs of lameness by the rider or trainer on the racetrack during or immediately after an exercise event (galloping or breezing). Diagnosis of lameness was confirmed by the attending veterinarian by use of a 0 to 5 grade lameness scoring system adopted by the American Association of Equine Practitio-ners.2 In this scoring system, grade 0 = no lameness; 1 = lameness is difficult to observe and not consistently apparent, regardless of circumstances (eg, weight carrying, circling, or traveling on inclines and hard surfaces); 2 = lameness is difficult to observe at a walk or when trotting in a straight line but is consistently apparent under certain circumstances (eg, weight carrying, circling, or traveling on inclines and hard surfaces); 3 = lameness is consistently observable at a trot under all circumstances; 4 = lameness is obvious at a walk; and 5 = lameness results in minimal weight bearing in motion or at rest or complete inability to move. For purposes of this study, horses assigned a grade ≥ 2 were classified as lame.
Anatomic location of lameness—Among horses confirmed as lame by the attending veterinarian, joint inflammation injury was localized by the detection of 1 or more of the following clinical signs: joint heat, joint effusion, or signs of pain elicited during flexion of the joint. Perineural or intra-articular analgesia was used to localize the source of lameness in horses without evidence of joint heat, joint effusion, or signs of pain elicited during flexion of a joint. Radiographic or ultra-sonographic examinations were performed in 10 horses (those with a lameness score ≥ 3 or those for which prescribed treatment failed to eliminate signs of lameness) to confirm the source of lameness.
Treatment of lameness—Injuries to the distal interphalangeal, metacarpophalangeal, middle carpal or antebrachiocarpal, distal intertarsal, tarsometatarsal, femorotibial, and sacroiliac joints were treated in the affected limbs with intra-articular injection of sodium hyaluronatea or methyl prednisolone acetateb and amikacin.c Estradiol cypionated was administered IM to horses in which patellar fixation was diagnosed.
Suspensory ligament injuries were diagnosed by detection of heat in the proximal palmar or plantar region of the distal portion of each limb, signs of pain elicited on palpation of the suspensory ligament origin, lameness (grade ≥ 2) while jogging, findings after perineural analgesia, and results of ultrasonographic examination. Injuries to the proximal suspensory ligaments of the forelimbs and hind limbs were treated with extracorporeal shock wave therapy every 7 days for 3 weeks in conjunction with intraligamentous injection of triamcinolone,e amikacin,c and a distillation of pitcher plants (Sarraceniaceae family).f Other soft tissue injuries such as synovitis of the distal digital tendon sheath were treated with injection to the affected area of triamcinolone, amikacin, and pitcher plant distillate.
Athletic performance at 2-year-olds in training sales—The official time of individual breezes in each horse was monitored by the electric timer operated by the racetrack clocker. At each sale, study horses were assigned into 1 of 3 groups (fast, average, or slow) on the basis of their recorded official speed, compared with the calculated mean speed of all horses at the same sale.3 Fast horses were those for which the race speed was faster than the sale mean speed. Average horses were those for which the race speed was equal to or slower than the sale mean speed by ≤ 0.4 seconds. Slow horses were those for which the race speed was slower than the sale mean speed by > 0.4 seconds.
Financial returns—For each horse, this variable was calculated as the sale price as a 2 year old minus the purchase price as a yearling minus the cost of training ($10,000) minus the cost of treatment of lameness (if any). One horse was not entered into a 2-year-olds in training sale because of a carpal chip fracture that occurred during training; the sale value of this horse was recorded as $0.
Data collection—For each horse, the following additional data were recorded: yearling identification number, foaling date, age (months), sex (colt or filly), purchase price, arrival date, breaking date, interval (days) from arrival to being broken, interval (days) from being broken to first day on the racetrack for training, interval (days) from first day on the racetrack for training to first breeze, furlongs galloped, furlongs breezed, lameness (grade ≥ 2), date of lameness diagnosis, anatomic location and treatment of lameness, days lost during training, athletic performance at the sales (fast, average, or slow performance speed), and sale price. A day lost in training was defined as a day when a yearling did not undertake training because of an injury, disease, rain, or absence of the rider.
Statistical analysis—Survival analysis was used to estimate median time to the first event of lameness during training. Simple linear regression was used to assess the relationship between number of new cases of lameness and days prior to the sale. Horses were assigned into 1 of 3 groups (fast, average, or slow) on the basis of the speed recorded at the 2-year-olds in training sales in relation to the sale mean performance speed. New cases of lameness 30 or 60 days before the sale were compared among groups by use of a χ2 test. Financial returns were compared among groups by use of a Kruskal-Wallis test. Other continuous variables (age, purchase price, interval from arrival to breaking, interval from being broken to first day at the racetrack for training, interval from first day at the racetrack to first breeze, furlongs galloped, days of training lost, and days on which the horse was lame) were compared among groups by use of a Kruskal-Wallis test. Values of P < 0.05 were considered significant.
Results
Thirty-seven of 40 horses were classified as lame during training. Joint injury was the most common cause of lameness (27/37 horses). In contrast, only 4 horses had lameness associated with disease of the dorsal portion of the third metacarpal bones (ie, DMD; Table 1). Eighteen of 37 horses had an injury to hind limbs only; 5 other lame horses had an injury to both forelimbs and hind limbs. Median time to first event of lameness was 137 days (Figure 1). The frequency of new cases of lameness increased as time (days) approached the date of 2-year-olds in training sales (Figure 2). Four of 11 horses classified as lame within 30 days prior to the sales were sold in February; those horses had lameness associated with the sacroiliac joint (n = 2), proximal suspensory ligament of the left forelimb (1), or DMD (1). The remaining 7 lame horses were sold in March. Three of the 7 horses had lameness in the hind limbs. Affected regions included distal tarsal, distal interphalangeal, and sacroiliacjoint in 1 horse; femorotibial joint in 1 horse; and metatarsophalangeal and distal tarsal joints in 1 horse. Four of the 7 horses had lameness in the forelimbs. Affected regions included the metacarpophalangeal and antebrachiocarpal joints in 1 horse; DMD in 1 horse; antebrachiocarpal and intertubercular bursa in 1 horse; and antebrachiocarpal joint in 1 horse. At the sales, 4 horses were classified as fast, 21 as average, and 15 as slow (Table 2). Median financial return was slightly but significantly (P < 0.05) different between horses classified as fast ($14,000) and average ($0) or slow (–$8,000). The median number of days of training lost in horses with an injury in the forelimb (14 horses; 13 days lost), in the hind limb (18 horses; 16 days lost), or in both limbs (5 horses; 15 days lost) was not significantly (P = 0.83) different.
Interval to first event of lameness (median interval indicated by arrow) among 40 yearling Thoroughbreds that were bought for the purpose of resale (after training) for profit.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Interval to first event of lameness (median interval indicated by arrow) among 40 yearling Thoroughbreds that were bought for the purpose of resale (after training) for profit.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Interval to first event of lameness (median interval indicated by arrow) among 40 yearling Thoroughbreds that were bought for the purpose of resale (after training) for profit.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Anatomic location of lameness that developed during training in 37 of 40 yearling Thoroughbreds that were bought for the purpose of resale for profit and were classified as fast, average, or slow at 2-year-old in training sales.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Anatomic location of lameness that developed during training in 37 of 40 yearling Thoroughbreds that were bought for the purpose of resale for profit and were classified as fast, average, or slow at 2-year-old in training sales.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Anatomic location of lameness that developed during training in 37 of 40 yearling Thoroughbreds that were bought for the purpose of resale for profit and were classified as fast, average, or slow at 2-year-old in training sales.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Distribution of new cases of lameness within 1 to 150 days prior to sale in 37 of 40 yearling Thoroughbreds that were bought for the purpose of resale (after training) for profit. The graph includes linear regression line (R = 0.37; R2 = 0.14; P = 0.16). Sales were of 2-year-old horses in training.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Distribution of new cases of lameness within 1 to 150 days prior to sale in 37 of 40 yearling Thoroughbreds that were bought for the purpose of resale (after training) for profit. The graph includes linear regression line (R = 0.37; R2 = 0.14; P = 0.16). Sales were of 2-year-old horses in training.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Distribution of new cases of lameness within 1 to 150 days prior to sale in 37 of 40 yearling Thoroughbreds that were bought for the purpose of resale (after training) for profit. The graph includes linear regression line (R = 0.37; R2 = 0.14; P = 0.16). Sales were of 2-year-old horses in training.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Discussion
The scope of the present study was descriptive. It was limited to 40 horses in 1 training center, the training procedures of which may not be representative of the population of horses trained in Ocala, Fla. The sample size in our study was low, and it may have contributed to the failure to detect significant differences in exercise variables (eg, No. of furlongs galloped 30 and 60 days before the sales) among horses classified as fast, average, or slow. Another limitation was that diagnosis of lameness was conducted by 1 veterinarian, whose accuracy for diagnosis of lameness by use of the 5-grade lameness scoring system was not assessed. Overall, the study results revealed that joint injury was the most common cause of lameness among the horses entered into 2-year-olds in training sales, the incidence of lameness in hind limbs was high, the frequency of new cases of lameness increased as time (days) approached the date of the 2-year-olds in training sales, and median financial return was slightly but significantly different between horses classified as fast ($14,000) or average ($0) and slow (–$8,000) at the sales.
Comparison of sex, age, purchase price, financial returns, and exercise variables in 40 yearling Thoroughbreds that were bought for the purpose of resale for profit and were classified as fast, average, or slow at 2-year-olds in training sales.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Comparison of sex, age, purchase price, financial returns, and exercise variables in 40 yearling Thoroughbreds that were bought for the purpose of resale for profit and were classified as fast, average, or slow at 2-year-olds in training sales.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
Comparison of sex, age, purchase price, financial returns, and exercise variables in 40 yearling Thoroughbreds that were bought for the purpose of resale for profit and were classified as fast, average, or slow at 2-year-olds in training sales.
Citation: Journal of the American Veterinary Medical Association 232, 1; 10.2460/javma.232.1.85
In the present study, incidence of lameness caused by DMD was low and incidence of lameness caused by joint injury was high. The reported low incidence of lameness caused by DMD may be explained by the training program, which included fast galloping (at a rate of 18 to 22 s/furlong). In a previous study,4 incorporation of breezing (at a rate of 13 to 14 s/furlong) during early training of Thoroughbred racehorses was associated with a decreased incidence of DMD. Slow galloping (at a rate of 30 s/furlong) may lead to tension on the dorsal surface of the third metacarpal bone, whereas breezing will result in compression on that surface.4 Horses that train at a slow-speed gallop will acquire bone that is adapted to that training modality and is susceptible to DMD.4 If the training pattern resembles racing, then the acquired bone will become adapted to racing without the horse developing DMD.4 Although daily breezing was not part of the training protocol of horses in the present study, the fast galloping (at a rate of 18 to 22 s/furlong) used at the study training center is considered faster than that used at other training centers in Ocala (typically, a rate of 30 s/furlong).
In contrast, the high incidence of lameness caused by joint injury in our study can be explained by repetitive loading during exercise. Traumatic synovitis and capsulitis are common joint injuries of athletic horses, presumably resulting from repeated trauma during ex-ercise.5,6 Acute synovitis affects synovial membrane diffusion and synoviocyte metabolism.7 Mechanically damaged synoviocytes release degradative enzymes, prostaglandin E2, and cytokines, which cause inflammation and disruption of joint homeostasis.7 Inflammation results in distention of the synovial membrane and effusion into the synovial cavity; because of increased intra-articular pressure in the affected joint, indirect stimulation of the capsular tissue receptors and subchondral bone receptors causes signs of pain.7
Among the horses of the present study, the incidence of lameness in the hind limbs during high-speed exercise training was considered high, compared with the incidence in adult racehorses, which most often develop lameness in or injure forelimbs.8 We offer 3 possible explanations for the reported high incidence of hind limb lameness in the horses of this report. First, the gait known as the racing gallop is asymmetric—the muscles of each hind limb initiate propulsion and the diagonally opposed forelimb completes deceleration to support the center of body mass.9 A brief period of suspension occurs as the body is propelled forward during each stride.10 Ground reaction forces in the forelimbs account for 60% of the total vertical impulse to support the center of body mass.9 However, the impulse (force × time) of horizontal propulsion for the body mass is greatest in the hind limbs.10 In the horses of our study, an asymmetric racing gallop combined with immature muscle tone may explain a higher incidence of lameness in hind limbs, compared with the incidence in adult racehorses. Second, in yearling horses, it is known that the frequencies of radiographic changes and arthroscopic surgery are higher in hind limbs than in forelimbs.11,12 However, the associations between radiographic changes, history of arthroscopic surgery, and lameness in pin-hooked horses have not been established. Finally, the high frequency of injury in hind limbs may also relate to the racetrack surfaces used in private training centers in Ocala. It is possible a deep sand cushion and limited daily pre-and posttraining maintenance are 2 potential factors that can lead to poor track surface quality. Poor track surface quality could demand greater effort by the hind limbs for horizontal propulsion; however, these associations have not been investigated by use of objective research methods to our knowledge.
Median interval to the first event of lameness during training was 137 days, which coincides with high-speed exercise training 30 days prior to the first sales. Visual assessment of a plot of the incidence of lameness in pinhooked horses revealed a linear increase of new cases during training, with the highest incidence evident within 30 days prior to the sales. Cyclic loading to an immature joint during exercise5 and cumulative rac-ing-speed exercise (breezing and racing) during the last 30 to 60 days prior to injury have been identified as risk factors for musculoskeletal injury in racehorses.13,14
Median financial return was slightly (but significantly) different between horses with performance speeds classified as fast ($14,000) and average ($0) or slow (–$8,000). This association was expected because speed is an important determinant in the selling price of 2-year-old horses in training. Median yearling purchase price was similar among 2-year-old horses classified as fast ($41,000), average ($30,000), and slow ($40,000), which is an indication that the association between speed and financial returns was not confounded by yearling purchase price. In a previous study,1 financial returns in 2-year-old horses were associated with training failure, whereas financial returns were significantly lower in 2 year olds that had a median of 38 days of training lost ($2,000), compared with 2 year olds that had a median of 10 days of training lost ($10,000). In that study,1 lame-ness was the main cause of training failure. In the present study, total number of training days lost during the training period or total days of training lost 30 days prior to the sale among 2-year-old horses classified as fast, average, or slow was not different. Differences in management of injured or sick (eg, ringworm infested) horses between the 2 study populations may explain this discrepancy. For example, type and frequency of medication used in pinhooked yearling horses during training was not reported in the previous study.1 In our study, horses that had mild lameness (grades 1 and 2) were medicated in an attempt to avoid loss of training days. Similarly, in our study, horses affected with ringworm were allowed to train, which resulted in no loss of training because of the parasitic infestation. In contrast, horses affected with ringworm in the previous study1 were not allowed to train to reduce risk of disease transmission.
ABBREVIATIONS
| DMD | Dorsal metacarpal disease |
Hylartin V, 20 to 40 mg (10 mg/mL), Pfizer Inc, New York, NY.
Depo-Medrol, 40 to 240 mg (20 mg/mL), Pharmacia & Upjohn Co, a division of Pfizer Inc, New York, NY.
Amiglyde, 0.5 to 2 mL (250 mg/mL), Fort Dodge Animal Health, a division of Wyeth, Overland Park, Kan.
Depo-Estradial, 5 mg (5 mg/mL), Pharmacia & Upjohn Co, a division of Pfizer Inc, New York, NY.
Vetalog, 3 to 24 mg (6 mg/mL), Fort Dodge Animal Health, a division of Wyeth, Overland Park, Kan.
Sarapin, 2 to 10 mL (0.17 mg/mL distillate), High Chemical Co, Levittown, Pa.
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