What is tie-up? Read this short article by Dr. Stephanie Valberg
Here is a description of what happens to the muscle cells from Dr. Sue Garlinghouse:
"The ion pumps (ie, sodium/potassium, calcium/magnesium and calcium/ATPase) in the membrane surrounding the muscle cell which move substrates in and out of the cell are disrupted, and so the interior environment of the muscle cells either cannot get rid of waste products of metabolism, OR has too much of a metabolic substrate to be able to function, OR can`t get enough of a metabolic substrate to be able to function. And so the muscle cell simply shuts down. When muscle cells shut down, they don`t do so in the relaxed position, they freeze up in the contracted position, which is why you get those rock-hard muscles. Biochemically, it`s not all that different from rigor mortis."
It is important to administer fluids because you need to help the kidney flush the waste products from damaged muscle cells. More from Dr. Sue (same reference: Exertional rhyabdomyolysis):
"The effect on kidneys comes in when the connective tissue (the sarcolemma) surrounding and enclosing the muscle cell is disrupted, releasing the contents of the muscle cell into the bloodstream. There are lots of different proteins and substrates and whatnot in a muscle cell, but the important one for this particular discussion is myoglobin. Myoglobin is a protein pigment which is responsible for oxygen transport in the muscle cell. Hemoglobin transports oxygen in the bloodstream, myoglobin transports oxygen in the muscle cell. When myoglobin is released from a disrupted muscle cell into the bloodstream, it travels to the kidneys and is filtered out. In being filtered out of the bloodstream (and keep in mind, there`s probably a lot of it from the kidney`s point of view), it causes (or CAN cause) kidney damage or even total renal failure by overwhelming and clogging up the kidney tubules and restricting the blood (and therefore oxygen) supply to the kidney tissue. This effect will be worsened if the animal is hypovolemic, meaning he`s dehydrated and therefore has a decreased total plasma volume. A decreased plasma volume means that in turn the blood is thicker and that the heart must work harder to circulate. And this in turn means that less oxygen to delivered to the muscles and organs, fewer substrates, less waste product removed, and so on. A vicious cycle sort of thing. So while myoglobin does not directly damage the kidneys, in great enough concentration it will cause damage indirectly by clogging them up and creating what is called myoglobinuric nephrosis and possibly renal failure. It`s also the myoglobin being filtered out that shows up as very dark urine."
Here is advice that my vet, Dr. Hubbard, got from Dr. Erica McKenzie, a vet who does research on equine muscle disorders and is especially interested in rhabdomyolysis in Arabians.
1) The absolute most important factor known to date to be associated with tie-ups in Arabian horses (in contrast to other breeds) is too much rest between and after workouts/events. She recommends having no more than one consecutive day of rest between workouts. This isn't to say that the horse should be worked strenuously two days after a 100 mile ride, but they should be exercised for even 20 minutes on the longe line (can't rely on turnout alone) to keep the muscles working and loose. From the work she has done she has determined that most horses tie up after a few days of rest following an event or following training when they were not worked out consistently for the days leading up to it. My own addendum to this would be in acknowledgement that this isn't always possible... so at least really focusing on getting her an easy longe 2 days after an event/training and consistently for a few days leading up to one at the very least.
2) She believes that diet plays less of a role in Arabians although she still suggests a high fat, low starch diet. I know you've added rice bran in the past and she is also a fan of supplemental oil in the diet for non-sugar calories.
Note: Other advice I have been given includes dramatically restricting grass intake (dry lot your horse) the week prior to a competition. Cool nights and warm days make the sugar levels really high defeating the purpose of the low starch diet.
From a diet perspective, I also use Equine Choice probiotic and Acid FX to help keep Luba's tummy happy and full of good bugs.
3) She recommends a supplement called Topline Extreme or as a back up SuperSport from Purina. Note: these products are only available in the US. The basic idea is a structural issue in the intracellular structural proteins within the muscle cell, so it contains some amino acids of a type that might be specially incorporated into those proteins. Scientific evidence based in human studies and currently limited (we know feeding protein supplements before and after exercise will upregulate intracellular synthesis, but do we know specifically this supplement will do that and in a horse, no, not at all, needs to be determined)."
4) She does believe dantrolene can help horses recover from tie-ups quicker, that it can prevent some muscle necrosis, and that it can be used as a preventative at the lower dose, always giving 60-90 minutes before exercise. She warns that overuse and high doses can lead to high potassium levels among the other known side effects.
We gave Luba 2 mg/kg of dantrolene twice a day after she tied up on Sunday. By Tuesday, her muscles were nice and soft.
A protocol from the University of Minnesota protocol says that once your horse's CK falls below 3000 U/L, you can safely start them back to work using dantrolene. By Thursday, Luba's CK had fallen to 2,000.
Here is the protocol that we are using now to return to work using dantrolene given 60 minutes pre-exercise daily:
2 mg/kg for 5 days (800 mg for 400 kg horse)
1 mg/kg for 5 days (400 mg)
0.5 mg/kg for 5 days (200 mg)
Once Luba has exercised successfully for 5 days at the lowest dose, we will stop the drug and check her CK 4-6 hours after the next exercise session. Dantrolene must be withdrawn well in advance of competition (60 hours for a 5 day regimen of 1 g per day according to CPMA Schedule of Drugs)
5) Interestingly she has learned from her research that even some of the most fit, and successful Arabian endurance horses have abnormally high CK (up to 10,000) following events despite looking and acting clinically normal! She suspects a genetic link somewhere there, so the research goes on!
