A LOOK AT RACETRACK BREAKDOWNS- 1991

Bill Johnson, DVM, Califomia Veterinary Diagnostic

Laboratory System

The California Veterinary Diagnostic Laboratory System (CVDLS) is a state- wide network of diagnostic laboratories with a central reference laboratory lo- cated on the University of California at Davis campus. There are four branch laboratories located at Turlock, Fresno, Tulare and San Bemardino.

The CVDLS provides a service to the state by necropsying animals and provid- ing blood and tissue analysis for the diag- nosis of disease. The U.C. Davis School of Veterinary Medicine operates the CVDLS through a contract with the Cali- fornia Department of Agriculture.

Because horse racing constitutes such a large portion of the equine industry in California, the California Horse Racing Board established the necropsy program of racehorses with the CVDLS. As of February 1990, all homes which die at California racetracks within the bound- aries established by the California Horse Racing Board are required to be necropsied at CVDLS to set up a data base of racehorse diseases and injuries. The goals of the necropsy program are to define the injuries racehorses suffer on California racetracks and to determine

Author's address: Equine Reseamh Laboratory, School of Veterinary Medicine, University of Cali- fornia, Davis, CA 95616. Acknowledgments: This paper was prepared through the U.C. Davis Equine Research labora- tory which receives fu rids from the Oak Tree Racing Association, the State of California satellite wager- ing fund and contributions by private donors.

e b ~ a p u l a (2) Pel~ is (9)

i (5

Humerus (1 O) - ~ ~ ~ , ~ F e m u r (1)

R ad ius (0) - ~ i '~ Ribs(l) "~ ,~STibm (2)

M etacarp_al(42) ~ Metatarsal (7) / ~ ~ Ruptured (C=,~..,,..) -'-fill)'~.. (c,~--~,,dF'-fff ) !~ Ligaments

P I . P2(9) ._ . . .~"-Sesamoid (64) )Jk / l.k (17)

avicular (1) (co1~ non,) Laminitis (5)

Location and Number of Musculoskeletal Injuries 1991

ways such catastrophic breakdowns can be avoided. After the CVDLS patholo- gists obtain their information, the tissues and samples are passed on to U.C. Davis veterinary orthopedic researchers for fur- ther evaluation and study.

Over the 1991 calendar year, 228 horses were necropsied, providing valuable in- formation on racehorse diseases and in- juries. The majority of the animals exam- ined were Thoroughbreds, followed by Quarter Homes and a few Standardbreds and Appaloosas. There was one case

where the breed was unknown. The breeds submitted for necropsy are as fol- lows: Thoroughbreds - 194; Quarter Horses 29; Standardbreds - 2; Appaloo- sas -2; unknown -1.

The majority of the horses examined were two-, three- and four-year-olds. More injuries occurred in the three-and four-year-olds (127 homes) than all the other ages combined. It is difficult to assess the significance of this number though because it may be due to the fact that three-and four-year-old homes con-

Table 1. Distribution of horses by age and breed.

Age (years

Breed 2 3 4 5 6 7 8 9 11 NG* total

Appaloosa 2 - 2

Quarter Horse 5 7 11 1 4 1 29

Standardbred 1 1 2

Thoroughbred 29 59 48 16 22 6 2 1 1 10 194

unknown 1 1

Total 36 66 61 18 26 6 3 1 1 10 228

Volume 13, Number 3, 1993 129

stitute the major age groups at the tracks and, therefore, the majority of the horses submitted for necropsy. Table 1 shows the age and breed breakdown of horses necropsied.

The horses were grouped according to age and the activity the horse was in- volved in when the injury occurred. Over- all, most injuries occurred while racing (45.1%) or training (36.4%). When bro- ken down by breed, it appears that with Thoroughbreds, injuries occur almost as frequently in training (43.7%) as they do in racing (40.2%). Although the numbers are much smaller, the limited data ob- tained on Quarter Horses suggests that they are more likely to break down dur- ing a race (58.6%) than during training (13.8%). The fact that so many Thor- oughbreds broke down during training, a time when the horse may not be running at peak exertion, may be worthy of addi- tional investigation.

Table 2 lists horses by age and activity prior to fatal injury. Table 3 lists horses by breed and activity prior to fatal injury. The non-exercise group represents those horses that died or were euthanized due to pneumonia, colic, founder, etc. The accident group included horses that jumped the rail prior to a race, collided with another horse, or were involved in what would be considered a "one of a kind" mishap.

As expected, the most common prob- lems affecting racehorses of all breeds are those of the musculoskeletal system (84.6% of all injuries). These injuries include damage to the muscles, ligaments, tendons or bones. Table 4 shows the breakdown of the different major body systems affected according to breed.

A complete breakdown of the muscu- loskeletal injuries of all breeds combined is depicted in Diagram 1. The diagram shows the general location of these inju- ries and in parenthesis, the total number ofinj uries to that particular location. Some of these horses had multiple sites with fractures. In these instances, the horse's injury was categorized according to the site most likely to have fractured first.

Table 2. Age in relation to activity prior to fatal injury.

Age Race Training Non-exercise Accident 2 7 17 11 1 3 28 29 5 4

4 36 16 6 3

5 12 5 1

6 14 5 5 2

7 3 3 -

8 1 2

9 1 -

11 1 - Not given 2 4 2 2

Total 103 83 29 13

Table 3. Type of injury by breed

Breed Race Training Non-exercise Accident

Appaloosa 2 Quarter Horse 17 4 6 2 Standardbred 1 1 Thoroughbred 83 78 22 11 not given 1 Total 103 83 29 13

Table 4. Primary organ system affected (listed by breed).

Breed Organ system affected Number Total

Appaloosa Musculoskeletal 2 2

Quarter Horse Cardiovascular 2 29

Digestive 3

Musculoskeletal 24

Standardbred Nervous 1 2

*Multiple System 1

Thoroughbred Cardiovascular 1 194

Digestive 8

Integumentary 2

Musculoskeletal 166

Nervous 1

Repiratory 6

Urogenital 1

*Multiple System 9

Not given Non made 1 1 Total 228

130 JOURNAL OF EQUINE VETERINARY SCIENCE

Table 5. Distribution of musculoskeletal injuries (listed by breed).

Breed Injury Number Total

Appaloosa Fracture, Carpal 1 2 Fracture, Sesamoid-Biaxial 1

Quarter Horse Fracture, Carpal 5 24 Fracture, Humerus 1

Fracture, Metacarpal 2 Fracture, Metatarsal 1

Fracture, Pelvis 1 Fracture, Sesamoid 2

Fracture, Sesamoid-Biaxial 5 Fracture, Skull 1 Hemorrhage 1

Laminitis 1 Ligament rupture 4

Thoroughbred Fracture, Carpal 6 166 Fracture, Humerus 9

Fracture, Metacarpal 40 Fracture, Metatarsal 6

Fracture, Pelvis 8 Fracture, Sesamoid 12

Fracture, Sesamoid-Biaxial 44 Fracture, Skull 4

Fracture, Femur 1 Fracture, Navicular 1

Fracture, P1 8 Fracture, P2 1

Fracture, Ribs 1 Fracture, Scapula 2

Fracture, Tibia 2 Fracture, Vetebrae 3

Laminitis 4 Ugament rupture 13

Myositis 1 Total 192

Table 5 has a breakdown by breed of the musculoskeletal injuries.

Ligament ruptures occurred most fre- quently in the front suspensory ligaments in the three- and four-year-olds. An analy- sis of affected limbs revealed that the front legs were more commonly injured than the hind legs. Previously, it was found that the right and left front legs were equally affected, but the current analysis revealed that the front left leg was affected slightly more than the right front leg.

The following explains the remaining

injuries and the body systems affected of all breeds. There were six horses with injuries to the respiratory system. Three had pneumonia caused by different in- fectious organisms. Two had bleeding in the lungs and one had pleuritis.

There were 11 horses with injuries to the digestive system. Six horses had coli- tis, two of which were caused by bacterial agents. The other four appeared to be "colitis x," a condition unique to horses; the cause is unknown. Two horses had colic. Two horses had ruptured stomach, one of which was due to a perforating

gastric ulcer and the other was associated with colic. One horse had a ruptured esophagus which was caused by a lodged foreign body.

There were three horses with injuries to the cardiovascular system. One horse had wide spread vascular thrombosis in several major blood vessels but the cause was undetermined. One horse had a rup- tured aorta. One horse had massive inter- nal bleeding similar to two horses necropsied in 1990. The cause of this condition, also reported in other states, is unknown.

There were two horses with injuries to the nervous system. Both horses had en- cephalitis. One of the horses was suffer- ing from a viral infection and the other developed a degenerative brain condi- tion caused by previous ingestion of a poisonous plant - yellow star thistle.

There were 13 horse with injuries to other body systems. Two horses had inju- ries to the skin (severe bacterial infection from an accidental puncture wound), one had nephrosis, two had septicemia and eight were listed as suffering from sud- den death syndrome and the cause was undetermined. The most significant cat- egory of this group was sudden death. These eight horses died during training and racing and no previous illnesses were noted.

The horses necropsied in 1990 and 1991 that had sudden death syndrome and massive internal bleeding both sur- prise and interest pathologists because the cause is undetermined. New exami- nation procedures are currently being implemented in an attempt to determine the cause of these unexpected deaths.

One of the more interesting findings of the necropsy program involved fractures of the humerus bone. It was found that most of these fractured bones had evi- dence of a previous incomplete stress fracture, identified by the presence of bony callus that resulted from the healing process. The incomplete fracture under otherwise normal racing or training exer- cise.

Incomplete stress fractures of the hu-

Volume 13, Number3, 1993 131

merus are very difficult for a trainer or veterinarian to detect because the horse may not show a distinct lameness and the mass of muscle coveting the humerus makes it very difficult to x-ray. More research is being conducted to help deter- mine the causes and characteristics of stress fractures.

The California Horse Racing Board has appointed to the racehorse necropsy program an industry-wide board of advi-

sors consisting of owners, trainers, track veterinarians,trackmaintenance officials, farriers and official California Horse Racing Board veterinarians. The board acts as a liaison between the public and the program to help direct further analy- sis of the necropsy program's informa- tion.

As the program continues, enough numbers are being collected and stored in

the data bank to analyze, in depth, the problems affecting racehorses and to look for common denominators of cata- strophic injuries. Further study supported by the Equine Research Laboratory is being conducted by equine specialism from the U.C. Davis School of Veteri- nary Medicine on various aspects of the necropsy findings. (From TheHorse Re- port)

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