| ultrasound |
 | 1) Diagnostic ultrasound: a technique that uses ultrasonic waves to image internal structures. 2) Therapeutic ultrasound: a therapy to create heat and stimulate healing. |
| under wraps |
| Horse under stout restraint in a race or workout to keep it from pulling away from the competition by too large a margin. |
| underlay |
| A horse racing at shorter odds than seems warranted by its past performances. |
| untried |
| 1) Not raced or tested for speed. 2) A stallion that has not been bred. |
| unwind |
| Gradually withdrawing a horse from intensive training. |
