Seminar – Research in endurance (Tevis study cont)
|March 25, 2014||Posted by Melinda under Uncategorized|
It’s been a whirl wind week since we chatted. I’m getting a taste of clinics and it’s boring, busy, hectic, frightening, etc. But, we aren’t here to talk about dairy cows and what the industry is or isn’t doing….so let’s get back to the conference.
Brief recap from the previous post: Remember that…
1. …chloride is king when it comes to possibly predicting future failure/success later on in the ride.
2. …with the exception of possibly heart rate, physical exam (PE) parameters during the vet check are not good predictors for success/failure later on in the ride.
The real question is: is chloride a better predictor than HR? If not….then there is no point in continuing to pull blood and explore chloride if the very non-invasive heart rate is as good or better.
That is what the Tevis studies in 2012 and 2013 set out to look at.
2012 was considered a “pilot study”. In general it seemed to confirm everything we already discussed in the previous post – Chloride is “king” and is a better predictor of failure as compared to other parameters. Total protein was a close follow up.
- The conclusion was that horses with increased dehydration, and increased elyte loss had an increase in failure rate.
- None of the PE factors were important.
Even though the 2012 and 2013 studies were essentially the same design, the 2013 study has an important difference – participation wasn’t REQUIRED – it was strictly voluntary whether you wanted blood pulled at Robinson.
This introduces a selection bias into the data of 2013 that was not present in the 2012 study.
Something very interesting occurred (at least I think it’s interesting….) in 2013 based on people being able to opt out.
- In 2013, those people that ended up in the rider option group were very unlikely to have blood drawn at Robinson.
- Those that were pulled over time were also over represented in the “did not have blood drawn” group.
So what’s a good predictor of failure?
The physical exam
Not reported factors (ie – stuff that wasn’t recorded on the vet card) was significantly associated with failure. Remember that the stats are only being evaluated at Robinson Flat (about 1/3 of the way through the 100 mile ride) and then being used to predict failure at later points in the ride. So this isn’t a case of a vet seeing a lame horse and then not bothering to record the rest of the parameters – these are horses that are being cleared to continue on in the ride that are missing “stats” on their cards at this point – such as jug fill, anal tone. There was some discussion on why this might be – perhaps the vets are concerned with something else on the PE that is occupying more of their attention.
The worst predictors (ie, not helpful at ALL) are skin tent, muscle tone, tack galls. The list doesn’t surprise me. If you could have asked me what I thought the worst predictor was in the PE exam of future failure, I would have named skin tenting. SO variable. Muscle tone makes sense to me as well, considering how subjective it is depending on the vet scoring it.
The next worst predictors were back, cap refill, gait, gut sounds, attitude, mucus membranes, overall impression. In a bigger study some of these might result in being significant, especially the ones at the end of the list (they are listed in order of worst to not so worse…). I asked whether a power study had been done (let’s you know how many subjects you need to get significant results at the end) and while he didn’t know, when I asked for a “gut feeling” he said 400-500 horses. (Tevis has about 200 horses).
The best predictors on the PE for predicting later failure were jugular refill, anal tone (but often not recorded, so must interpret whether this is a good predictor with caution), wounds (same caveat as anal tone), heart rate, and heart rate adjusted. The adjusted heart rate is an adjustment that accounts for how long the horse has been in the vet check before the heart rate was taken to compensate for additional recovery time. The heart rate for finishers was 52+/-5 versus 54+/-4 for nonfinishers. When looking at heart rate adjusted (HR + #min waited based on PNR and in-time) the rate for finishers was 57+/-8 versus 61 +/-7 for nonfinishers. As you can see, even though HR (especially adjusted heart rate) is a good predictor, there is significant overlap between the categories of finisher and nonfinisher……It would be difficult to establish a cut off time based on heart rate that captured horses likely to get pulled, while excluding horses likely to finish.
In 2013 (as in 2012) PCV, sodium were poor predictors for reasons already discussed. The next worst are BUN and bicarb (bicarb could possibly be more significant in a larger study).
Chloride and TP, which were found to be good indicators in the 2012 study were also good indicators in 2013. This is very exciting because it means that this finding was repeatable. Remember that low chloride (chloride is lost in the sweat in large quantities in endurance events…) is associated with failure (getting pulled). However, dehydration concentrates the blood….which can make the chloride actually look higher than it really is in an individual horse. So, they came up with a way to adjust the chloride value based on the total protein (TP). TP increases in dehydration because the blood is becoming more concentrated. So, by combining Cl and TP (something they called a “corrected chloride”) they came up with a number that was very well correlated with whether a horse would go on to be pulled later on in the ride.
How good was it in predicting who would go on to be pulled at some later point? If a horse had a corrected Cl value of less than 84…there was a 70% chance of being eliminated from the ride at some point. If the corrected Cl was less than 80, there was a EIGHTY percent chance of being eliminated at some future point.
For comparison….looking at heart rate, which was the most significant PE parameter in predicting success, the best that we can do is predict about 40-45% elimination.
If someone told me at Robinson Flat before I went down into the canyons that there was an 80% chance that I would be pulled from the ride at some point, I probably would elect to ride another day. Considering that with heart rate the best they can do is somewhere in the 40’s….I would probably take my chances in the canyons and beyond.
Lameness versus Metabolic
The lameness and metabolic pulls were all pooled in the statistics above. One thing that was mentioned is that while we code pulls as “lame”, “metabolic”, “rider option” and that these are good from a practical standpoint, when the data is actually analyzed, there are no “hard and fast” rules that a lameness pull couldn’t actually be better classified as a metabolic pull and vice versa. Some other interesting facts:
- In both years, when rider option vet card/blood work were evaluated, these pulls often fit better into the metabolic pull group from a statistical standpoint.
- I *think* he mentioned that overtime pulls also resembled metabolic pulls – but I don’t have it written in my notes so I could be remembering incorrectly.
So what now?
Unlike PE parameters the blood work has been done blinded to the rider up to this point. While we (as the rider) might change how we manage our horses between now and the next check depending on what the vet says at this check (which may be one reason the PE parameters are not as significant as they could be….), since we don’t know what the blood work says, then we can’t respond to it. There was a lot of discussion of how we might use the information. Create statistical cut off values to generate chances of failure and present as FYI to the rider? Actually pull horses based on the numbers (this was specifically cited as something that is NOT being considered right now)?
The biggest danger seems to be using the numbers as a diagnostic for “treatment” – ie the rider supplementing electrolytes based the serum results. I think as riders we have a tendency to want to “do something” when we see numbers or scores – and I think while we are at the point in our knowledge that while perhaps they can say that this is or isn’t that horse’s day – attempting to correct a low chloride or respond in a specific way to manage the chloride/electrolytes based on the numbers during a ride was called “dangerous”. For example, chloride may actually be a flag/marker for something else and NOT something that can be fixed and have everything be OK.
We know dehydrated horses get into trouble. We know that chloride and TP can indicate something is going on. But there’s a lot of mystery in the black box right now.
That’s it for tonight folks. I’m loopy and exhausted so I’ll finish up the rest of the research presented in the next post. That’s it for the Tevis study, so we will move onto some other recent studies next (good news for those of you sick of hearing about Tevis already and are dreading the invariable Tevis buzz in the next 5 months).
Edit: Gail asked the question in the comments that reminded me of 2 really important points I had meant to cover in this post, so please be sure to scroll down and take a look at my response regarding why the statistical tests are only useful at large rides with an increased pull rate, and why the PE exam is still very relevant (may not be as predictive – but it’s an important assessment of where the horse is RIGHT NOW). (on a side note, 8 hours of sleep is magical and I’m feeling SO MUCH BETTER this morning!!!! Yeah!).