Chapter 106The North American Thoroughbred
Description of the Sport
The commercial market is a straightforward avenue for owners to buy a high-quality racehorse without maintaining broodmares. The September Keeneland yearling sale offers nearly 5000 yearlings over a 10-day period. Numerous other sales are conducted throughout the year. Presale examination is an important part of veterinary practice at racetracks (see Chapter 99). The auction environment can be an extremely high-pressure setting for the veterinarian because the knockdown price may reach millions of dollars.
Track Surface and Lameness
Track surface is an important factor in the development of lameness and frequently is overlooked or neglected in lameness discussions (PJM, MWC) (see Chapter 105). Track surface dictates frequency and type of lameness. Injuries are often blamed on track surfaces, but musculoskeletal injuries are multifactorial. Shoeing, medication, training patterns, commercial breeding, and many other factors have all been implicated in the high injury rates in race-horses, and as often as not injuries cannot be fairly blamed on track surface (RMA, JAB). The most important factor in fatal racing injuries is not the track surface, but the horse (RMA). Almost all horses that develop fatal musculoskeletal racing and training injuries have evidence of preexisting pathology at the site of the fatal injury. They are repetitive stress injuries. Regardless, track surfaces play an important part in injury development, and the veterinarian needs to appreciate the types of injuries that are likely to develop in the track surfaces in his or her practice area.
Many European horses that previously trained on grass now race in North America. Most race and continue to train on grass, but some make the switch to training and racing on dirt successfully (see Chapter 107). Our impression is that European horses appear to have fewer forelimb and more hindlimb lameness problems than North American TBs. European horses often train on long straightaways, and this, combined with a forgiving surface (grass), is a situation different from training on dirt in North America. Horses bred to race on the turf appear to have an inherent conformational difference that allows superior performance on grass. Synthetic racing surfaces fall somewhere between dirt and turf relative to horse surface preferences. Turf horses are much more likely to be competitive on synthetic surface, even if they do not handle dirt tracks. Just as there are horses that do well or poorly on dirt or turf, there are horses that handle synthetic surfaces well and horses that do not.
Lameness Examination
Palpation
The hands should be run lightly over the back to assess for sore or tense muscles. The lumbar and sacroiliac regions, gluteal muscles, and greater trochanter of the femur should be palpated from each side. Although the process appears hazardous, the gluteal muscles and greater trochanter also should be palpated from behind. If necessary a forelimb can be elevated. Firm pressure should be used to detect gluteal myositis or trochanteric bursitis. Standing behind the horse is the best way to compare effusion of the femoropatellar joints. Each hindlimb should be examined in the standing and flexed positions. The Churchill test should be performed bilaterally (see Chapter 6). A positive response suggests distal hock joint pain. Negative findings on palpation and manipulation do not eliminate a joint from consideration, but positive findings often point to the source of pain causing lameness.
Movement
The usefulness of flexion or other manipulative tests is debatable. Lameness may be exacerbated, but disagreement exists over what a positive response means. For instance, when performing fetlock flexion, a positive response is common even in horses with lameness unrelated to the fetlock joint (RMA). One of us (PJM) finds fetlock and lower limb flexion tests worthwhile, but not carpal flexion, and finds hindlimb flexion tests nonspecific. One of us (MWC) finds forelimb flexion tests useful but finds all but the lower limb flexion test in the hindlimbs questionable. Finally, one of us finds the carpal flexion test the most specific and accurate flexion test; horses with a positive response generally have carpal region pain, and there are few false-positive results (MWR; see Chapter 8). Hindlimb flexion tests lack specificity (MWR). Each clinician needs to develop a protocol and be consistent.