Seminar report: current research in endurance horses
| March 14, 2014 | Posted by Melinda under Uncategorized |
We are going to skip over Dr. Marcella’s muscle injury seminar and do Dr. Langdon Fielding’s research seminar first.
For this and all the posts that contain seminar content summaries, the information presented is my best recollection based on my notes taken during the seminar. I try to be very clear where I am editorializing and deviating from strict reporting of what was said and presented. Any errors/differences from what was actually said are mine alone, with apologies to the presenter.
I walked in 10 minutes late to the lecture, so I missed the first set of slides, and came in hearing that to increase your chances of completing an endurance ride:
- choose the right breed
- incorporate enough rest in your program
- have a decent body condition score (no skinny horses!)
- chose the right distance.
Sounds easy huh?
Notice that he didn’t say you have to ride an arab. It’s just that choosing an arab means that statistically you are more likely to have success if you measure success as “finishing endurance ride”.
I’m not sure what studies he was referencing at the beginning for this information, but apparently (as perhaps we all suspected?) endurance is all about making good decisions that involve choosing a suitable horse, not overriding or under feeding, and choosing the right distance for the day.
Moving on from the obvious and onto less intuitive observations.
The basic questions that we are trying to answer by pulling blood at races like Tevis, and comparing vet check physical exams (referred to as “PE” for the rest of the post) is whether there are certain parameters in either method that can accurately predict whether a horse will be fail (ie be pulled) later on.
After all, if the non invasive PE is just as useful in predicting failure or success, why draw blood?
It terms out that the PE is rather bad at predicting whether a horse will go on to succeed and fail later on in the race.
It’s good for telling us how that horse is doing RIGHT now (is it colicking? is it lame? is it in trouble RIGHT NOW?), but almost completely useless for predicting how well the horse will do later on.
For example. Just because your horse has a “C” on it’s skin tent at this check doesn’t make it any more or less likely to get pulled later on down the trail than your friend whose’ horse has “A” skin tent.
Essentially the only PE parameter that may be useful is heart rate (HR). The HR your horse has at the vet-in pre ride is useless as a predictor….but increases in HR during checks during the race may be associated with a risk of pulls later on. It was also noted that HR is one of the few objective things that are measured during the PE, which may be a reason it’s more statistically useful/relevant. (CRIs, gut sounds were debated as possibly useful – but were not repeatable in various studies).
One reason that PE parameters might be such BAD as predictors is because we as riders are able to see those scores and then “do something” about them. The information caused us to change, which is NOT a good for playing around with the data and getting it to mean something.
Something that was emphasized, that has been pounded into me in school, and that I have tried to emphasize to my readers here – is that it is very difficult to accurately assess hydration on a PE. Unless the horse is at least 5% dehydrated it won’t show any signs of dehydration – which in an 800 pound horse is about 10.5 gallons. When you do start seeing signs of dehydration, deciding how severe it is a bit of a crap shoot. Considering that ALL horses finishing 50-100 mile races will be dehydrated to some point, the only question is HOW MUCH….and THAT my friends, is something we are really really really bad at quantifying on a PE. Which is unfortunate because hydration is absolutely critical to how a horse is performing. By the way……everyone agrees that dehydrated horses get into trouble…..but exactly HOW is unknown. Is it a preride thing? A training thing?
There are 2 parameters in a blood test we can use to access hydration – PCV (packed cell volume) and TP (total protein). PCV is the number of red blood cells suspended in plasma, and TP is the amount of protein in that plasma. As you get dehydrated you lose plasma volume (see my acid base balance posts for more information) – and thus the concentration of red blood cells and protein in your blood will INCREASE.
In horses the PCV can increase for reasons unrelated to dehydration – such as dumping extra red blood cells into their circulation when they are stressed. So, PCV not so a good indicator of hydration in horses.
TP DOES happen to be a decent indicator and is more accurate than PCV. Yeah!
Is there anything else that could be used?
- SAA (serum analog A) is a marker of inflammation. It one study it’s value was 412+/-144 in successful horses (horses that completed) and 5810 +/- 2243 in eliminated horses. Potentially a cut off value of a 1000 could be used? Monitoring levels of SAA may be more useful in training than in competition.
- Preride sodium concentrations higher in finishers in some studies. However, sodium levels in general are problematic when trying to assess them in conjunction with performance/success versus failure. Remember from previous posts that sodium and water are best friends. Where one goes, so does the other. A low sodium test level does NOT necessarily mean you have low sodium and need to supplement electrolytes. A high sodium “test” does NOT mean you need to stop electrolyting. All the sodium results have to be evaluated in conjunction with water, which makes it a poor absolute value.
- Lactate is usually mildly increased, and is NOT predictive. Lactate levels are better used as training and conditioning tools and not particularly helpful at rides (which makes sense to me since Hinchcliff says that central fatigue and electrolyte balance is more likely a limiting factor of performance in endurance horses than lactate levels – again, this was covered in the acid base balance posts so go read those if you want more info!).
- Bicarb – is consistently low in endurance horses, but not consistently low in sick endurance horses. Thus not especially useful for differentiating those horses that will get into trouble and those that will not.
- Glucose – inconsistent
- BUN – often increased
- Creatinine – often increase, may have some value as a predictive value.
- Potassium – is always decreased in endurance horses. Not a good predictor. There was an interesting aside about how there may be a genetic predisposition to developing decreased K at rides? Or perhaps management issues? But as interesting as that might be…..fact remains that K is a poor predictor and so we are moving on!
- Chloride – Dr. Fielding presented chloride as KING of elytes in the endurance horses. “Chloride is where it’s at”.
Let’s do a quick refresher on chloride. Chloride is present in increased concentrations in sweat. While sodium is also lost (remember that horse’s are not as efficient as humans as filtering out sodium, so some sodium is lost in sweat – but so is water – so while total sodium amounts decrease, the concentration of sodium in the blood remains about the same) chloride is lost in large enough amounts in the sweat that it results in both a decrease in total amount of chloride AND a decrease in chloride concentration in the serum. (Here’s a post that details the mechanisms for those of you that need a refresher. Scroll down to the bold section titled “Acid-Base Disorders“. From this point I’m going to assume that you are comfortable with the mechanism behind why endurance horses – which sweat a lot – lose so much chloride.). As a horse rehydrates (drinks water), this dilutes the already low chloride concentration making the concentration even lower. A decrease in chloride is a unique feature of endurance horses and is an unique feature of sick endurance horses (unlike bicarb). Chloride also has huge secondary impacts on acid base balance (again, refer to the previous post that was referenced and linked). Chloride measurements just might be the thing we are looking for…….to be continued.
I budgeted one hour to write a post before I needed to focus on school work again, so we must end here and pick it up in the next post. This post covers most of the preliminary information that he presented before going into the details of the 2012 and 2013 Tevis results. If you aren’t interested in Tevis or electrolytes…..do not fear! Other current research related to endurance was presented after the Tevis results, so stayed tuned and I’ll get there eventually.
