I heard from a client that her trainer has all horses competing at Preliminary and above (eventing) tested for blood enzyme levels at the start of show season. I was so impressed to hear that such comprehensive care is being given to the horses at her barn. I think it is a great idea to monitor your horses blood when he is in an intensive conditioning program. Two important muscle enzymes can be tested for. By studying these enzymes, veterinarians are basically trying to assess whether or not the horse has tied up, or if the horse has early signs of tying up.Other factors which can contribute to tying-up include vitamin E and selenium deficiency, and electrolyte imbalance. A horse with any of these imbalances is more prone to injury and cramping, as muscles cannot perform efficiently, thus leading to overloading of the tendons.