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Digital Cushion
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Pauline Moore
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 Posted: Sun Apr 11th, 2010 03:15 am
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Charlotte - Not much research has been done on chromium for horses, my supplier consulted a well-respected equine nutritionist here who sent back information that a maximum of 5mg per day for a 550kg horse is regarded as safe.  Chromium is one of those minerals that can be toxic in excess so I'm careful not to exceed this 5mg per day - my horses all weigh more than 550kg so I figure this gives me a bit of a safety margin.  I also feed brewers yeast for the B vitamins but that also contains a small amount of chromium so it's important to account for chromium from all sources until any further research proves that higher amounts are safe.  I use chromium yeast - this is yeast that has been grown in a chromium-rich environment - 5 grams (1 tsp) of chromium yeast contains 5mg of pure chromium.  I change the amount of magnesium depending on grass/weather conditions, always seeking to feed the least amount possible to achieve the desired effect.  Trial and lots of error has taught me I must increase magnesium on the day it starts raining, not wait for the new grass shoots to appear a couple of days later.  When the ground dries out again I drop the amount back down again.  This works for the conditions I have here but may be different in your part of the world - there are no foolproof rules, let your horses tell you what they need.

Leah - this horse has been with me for 13 years, 3 different properties with differing soil types but all within a 2hr drive of each other.  Over those 13 years we have regularly been though cyclical droughts and floods - times of no pasture, times of abundance.  Previously he has always been at his best in drought, the more severe the drought the better he was.  Starting towards the end of last year, we have had more rain than in the past decade, the very conditions when he is usually at his worst.  Knee-deep grass which has been seeding for the last month or so, damp conditions that are ideal for mycotoxin growth.  He is better now than in the worst of the droughts we ever had and has never before changed in digital cushion size and function - this change is dramatic. 

Best wishes - Pauline

DrDeb
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 Posted: Sun Apr 11th, 2010 10:32 pm
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Pauline, I fixed the measurement on Sol in your original post.

To answer the question you asked in your last: yes, there is definitely a higher incidence of ringbone among horses living on the sand. It's interesting that Bowker finds diminished circulatory perfusion in horses living on sand, comparable to horses that are standing too much on the rim, because the sand does nothing but push up into the soles, letting the rims cut in, so I don't understand that result. My interpretation of the ringbone is that it develops not from abnormalities in the more distal part of the foot; the ringbone is above and outside of the capsule anyway. The cause of ringbone is, just as you say, usually to be attributed to trim that is mediolaterally unlevel, so that you get one side of the foot striking early and the other side late. The late side experiences 'jerk' which affects all the collateral ligaments and the extensor process of the suspensory ligament, and this hyperstimulates the osteoblasts living in the periosteum where these ligaments attach, so that they start calcifying the ligament fibers where they root into the periosteum. Sand footing, because it is unstable, creates exactly the same effect, even in feet that if you took the horse out of the sand and stood him up on concrete, would have feet that were trimmed in perfect ML balance. Long and short is that I'm glad I finally moved my horses out of the sand.

I want to say that we are DEFINITELY 'going somewhere' with this discussion, for anyone else reading it. I am interested in Pauline's on-farm experiments and results, and I'm also interested in what Dr. Bowker is saying, for a reason. And this reason is: years ago, I began teaching students that a normal foot is shaped like a section of a tilted cone. This means that the tubules of the heel in a horse's foot should always be at least a little more upright than the tubules of the toe. It also would demand that we regard any flexure in the line of the coronet band as being abnormal; or to put it the other way around, the line of the coronet band should be straight. The coronet band should be described in 3 dimensions as tracing the edge of a single plane passing through the coronet of the toe and bulbs of heel.

Another way to view this is that there should be no 'zone of impingement' of the tubules in the quarters. There should be no flare that has been forced into the quarters by the forward migration or forward collapse of the heels. Ovnicek puts it that the bars should not be 'curly', i.e. warped into an 'S' shape due to the heels pressing forward against them from the rear. This all is discussed in the 2003 "Inner Horseman" back issue disk on orthopedic principles in farriery.

Now, when Pauline says I am 'pedantic' about hoof trim, that's an understatement I think my farrier would say and LOL. But I don't really need to lean on my farrier to do things right; he's taught me a lot, and I think he's a brilliant trimmer. I have seen Bob Anderson take a horse with totally ruined feet -- heels completely crushed under, no depth of sole, no depth to the foot as a whole, angle way too low like a duck's foot, and in about three years of just doing nothing more than "winning a little bit" with each trim, cause the foot to reshape itself to normal again.

Now, by 'normal' here I mean that the tubules of the heel are no less than parallel to the tubules of the toe, that the toe and wall depth are appropriate for the size and weight of horse, that there is no rotation either + or - in the coffin bone, and the horse moves sound without shoes.

HOWEVER this business of the thickness and rearward extent of the digital cushion are factors that I had not considered before. I listened to a Bowker talk myself some years ago, where he talked about sole depth in feral mustangs vs. domestic horses. The sole depth and DC factors appear now to work the same: which is in a nutshell to say, 'the more the better'.

In this series of posts, I therefore put up a couple more examples that ought to provoke us to some more thinking.

The first set is an X-Ray of the right fore and accompanying photos of the external appearance of a feral mustang from Nevada, a horse that never saw a day on soft ground in its life. All the substrate where it lived is glacial outwash rock, or pediments formed by the avulsion of Pleistocene lakes, or 'deflation terrains' created by the wind which is constantly blowing sand-sized particles away; or else outright basalt rock or other outcropping bedrock. There are some 'sand blows' on that range too, but they're the size of swimming pools and the horses roll in them, they don't run on them.

The second is an X-Ray of old Painty that I dug up. This was taken years ago, after he had been in bar shoes for years. The shoes were removed in order to take the XRay. This was right after I'd hired Bob, and he requested XRays before beginning, so he'd have the best chance of forming a good treatment plan for Painty.

Now I would like you-all to look at all of these as I have, and ask where we are going to find a foot that has more than about 35% 'heel extent', i.e. the ratio between length of coffin bone measured parallel to its solar plane : total length from toe of coffin bone to farthest apparent posterior edge of the bulb of heel. I don't see as much difference as my enthusiasm for Bowker's ideas would make me wish! One would expect the mustang to present a paradigmatic example, but it does not -- you can see this with your eyes, plus here are the measurements:

Mustang: 1.483 units heel length/4.412 units total = 34% heel length

Painty: 1.201 units heel length/3.934 units total = 31% heel length

Oliver: 5.661 units heel length/15.108 units total = 37% heel length, i.e. greater than the mustang!

Something must be amiss!! But I still think we're onto something here, and I think Pauline has discovered it. The one thing I definitely DO see in the mustang is an obviously DEEPER digital cushion; look at the external photos, rear view, and compare that to the equivalent views of Oliver and Pauline's horses, even her best 'rock stomper'. And of course, look at the solar view of the mustang....with its amazingly big, wide frog.

So here, I think, is the way to go. I tried to get some kind of estimate of DC depth or its volumetric size by measuring on the XRays, but there is no reliable way to see anything really but the cartilages. You don't see the DC itself. So this needs to be calipered from the outside. Now we'll have to guesstimate for the mustang, but I would be willing to say that at minimum he would have calipered 7 cm, i.e. about twice as thick or deep as Oliver and more than even Pauline's best.

I also think that the most useful thing to compare this thickness against is not any dimension of the foot, but the horse's weight. So, for exmple, if we have:

Oliver -- 1050 lbs. with 4 cm DC (worst forefoot) he would 'score' 3.8 cm DC per 1,000 lbs. weight.

Painty -- 1300 lbs. with 5 cm DC (worst forefoot) = 3.8 cm DC per 1,000 lbs. weight

Mustang -- 900 lbs. with 7 cm DC (estimated) = 7.7 cm DC per 1,000 lbs. weight

....and Pauline, please if you will do this calculation for your four so that we can compare.

What is SO interesting here is that we are liable to wind up concluding that a horse has to have at least (let us say) 3.5 cm DC per1000 lbs. weight. This is in exact parallel to what we previously found we have to have in terms of bone-tendon circumference, i.e. the absolute minimum for very heavy horses is 5.5 in./1,000 lbs. mass, the minimum for racehorses is 7.0 in/1,000 lbs. weight, and the desirable amount for riding horses is 8.0 in/1,000 lbs. weight; while the feral/wild populations continue to show not less than 9, and often as much as 14 in. of "bone" per 1,000 lbs. weight, in other words, from a third-again to twice as much as the domestic population.

Now I want to go about pinching every heel I can get a caliper on! This would be just as easy and no more impractical than the study we did here before on bone-tendon circumference, which any owner can do externally with no need of XRays.

One of the questions that studies of mustang and brumby feet raise is whether it is even possible for domestic horses to present what feral horses present. For as soon as anyone adopts a mustang and starts keeping him in a pen or a stall, or even under normal conditions on a ranch out West, within a couple of years the mustang's feet reduce in size and thickness, sometimes quite a bit. So there is no question that substrate and mileage upon the substrate is a major determining factor.

That in turn raises the further practical question of, 'OK if I'm keeping a domestic horse under domestic conditions, what kind of foot should I demand.' The answer to this is, I think still, 'the more the better': the thicker the DC, the more substantial 'bone', the greater rearward extent of the back of the foot, the better.

What we have done by just looking at a few feet here is to establish a ballpark parameter for what would be the minimum, i.e. somewhere about 3.5 cm/1,000 lbs. weight for the DC. That's exciting because it is useful and practical!

Everyone's further comments welcome -- Dr. Deb

 

 

 

Attachment: Forum Feral Mustang XRay Rt Fore cprsd.jpg (Downloaded 710 times)

DrDeb
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 Posted: Sun Apr 11th, 2010 10:33 pm
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External views of the same foot (right fore) of the same mustang in the above XRay.

Attachment: Forum Feral Mustang med et post cprsd.jpg (Downloaded 708 times)

DrDeb
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 Posted: Sun Apr 11th, 2010 10:34 pm
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Sole view of the same foot (right fore) of the same mustang in the above XRay.

Attachment: Forum Feral Mustang sole Rt Fore cprsd.jpg (Downloaded 708 times)

DrDeb
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 Posted: Sun Apr 11th, 2010 10:36 pm
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Painty's XRay, left forefoot, lateral view. I've had to extrapolate and draw in the heels, since the XRay did not take in the entire foot. You can clearly see the cartilages because Painty had a moderate case of sidebone so the cartilages have diffuse deposits of calcium and are thus fairly radiopaque -- this allows me to draw in the heels fairly accurately.

Attachment: Forum Painty left fore XRay heels extrap cprsd.jpg (Downloaded 708 times)

Leah
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 Posted: Sun Apr 11th, 2010 10:48 pm
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Dr Deb-I am drooling over those photos and rads.

Do you have any others of wild hooves that you would be willing to share to compare?

Also do you know why the Nevada horse was killed and how long he had been captive before he was killed (if at all)?

Last edited on Sun Apr 11th, 2010 10:51 pm by Leah

Leah
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 Posted: Sun Apr 11th, 2010 10:49 pm
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Also Dr Deb-this may be somewhere and I missed it.

Would you mind sharing the environment, diet, turnout, etc of your horses? Or more accurately what it was at the time the rads were taken.

I also like having the complete picture when viewing rads and hoof photos.

Pauline Moore
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 Posted: Mon Apr 12th, 2010 12:38 pm
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Dr Deb - Been pondering on this all day so have a few more comments.

Made some more phone calls to people I know to have been at Bowkers seminars to see if there is something I've missed regarding coffin bone:DC length ratios.  So far no-one can recall hearing how Bowker came to those recommended figures - whether he has actually seen this in a live or dead horse, or whether it's an idealogical extrapolation of what he believes to be optimal.  IIRC he did spend time in the desert (Nevada? with Gene Ovnicek?) looking at feral horses.  I agree with you that it would be hard to imagine a horse with a larger palmar foot than that on the mustang x-ray you posted.  Do you know the age of that mustang?  Did anyone look at his teeth to assess age when he was killed?  I ask because the only possibility I can think of that would explain the mustang's internal ratios being similar to Ollie's would be if he were a young horse, less than 5 years old.  Bowker stated that until 4 to 5 years old the DCs of 'good footed' horses are not differentiated from those of 'bad footed' horses.  It is only after that age that the DC starts to develop fibrocartilage if given the right conditions.

I definitely agree with you that estimates of depth and a feel for texture is more meaningful, particularly if we can relate that to the weight of the horse - brilliant idea!  This would be a very useful 'rule of thumb' so I hope we can motivate as many people as possible to invest in some calipers and go out looking for horses to 'pinch'.  Horses with contracted heels could perhaps be put into a separate category as a DC that is squashed into a tall, thin shape by the pressure of the ungal cartilages would give a misleading impression of being deep.  It would be good if we could find some way to assess texture also - a reasonably deep DC that feels very soft will be mostly fatty tissue with little fibrocartilage.

Here are the scores for my horses based on the flatter foot of the fores and hinds:

Rory - 19 yr old - 1280 lbs
Fore:  51 mm = 3.9 per 1000 lbs
Hind:  45 mm = 3.5 per 1000 lbs

Sol - 6yr old - 1320 lbs
Fore:  60 mm = 4.5 per 1000 lbs
Hind:  51 mm = 3.8 per 1000 lbs

Gante - 12 yr old - 1200 lbs
Fore:  69 mm = 5.7 per 1000 lbs
Hind:  60 mm = 5.0 per 1000 lbs

I've included scores for the hind feet also as I'm thinking there may be some significance in these measurements independent of the front feet. 

Your comments about Ollie's back feet have prodded me to think about this today.  I see a lot of horses whose problems are emanating from their back feet, usually a very obvious collapsed/underrun heel, but not infrequently back feet that look OK until inspected very closely - the degree of discomfort seems disproportionate to the extent of the foot problem but I have not been looking at DCs in the back feet specifically.  When the back feet have a negative plane orientation to the distal phalanx there is usually a distinct, quite sharp 'V' shape to the spine at the point where the withers should be smoothly blending into the back - the horse is bracing his back in a manner that is quite different from bracing due to front end soreness.  Anytime I see that shape to the withers/spine I'll check out the back feet before anything else.  The horse in the photo below does not have underrun back feet (the 'V' in his spine was from bracing due to a toxicity issue that nevertheless made him sore and stiff in his hindquarters - this was resolved and his back returned to its normal smooth shape within 6 weeks) but this horse does have shallow rear DCs and he does not like to canter - prefers to trot.  His owner phoned through DC measurements tonight:

LF - 60 mm
LH - 40 mm

RF - 57 mm
RH - 40 mm

He would weigh at least 1300 lbs which gives him a score of 4.3 for the front foot and 3.0 for the hinds. 

Ollie appears to have a rear DC score of 2.4 - I'm wondering if it is more than co-incidence that 2 horses with rear DC scores less than 3.5 are also 2 horses who do not want to canter.

This is the reverse of the laminitic horse who often prefers to canter because he can more easily get the weight off his front feet.  Do horses with uncomfortable back feet prefer to trot/pace so they can keep the weight off their back feet?

Best wishes - Pauline







Attachment: Hopper Aug 2009_12140180.JPG (Downloaded 678 times)

AdamTill
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 Posted: Mon Apr 12th, 2010 06:53 pm
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I'll contribute more later, but I thought I'd throw up a few images until I get a chance.

First, rehab on heels for one horse. Note the pinched, v-shaped look to the outline of the heels in the before picture, and the wide rounded u-shape in the after. The third is my current horse, who has always had nice wide heels.



Dr Deb's xrays:


Sam
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 Posted: Tue Apr 13th, 2010 09:02 am
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The image of the mustang foot is most helpful.

I have run around doing the pinch test on my equine collection today.  I have taken no measurements but will do so.  All show a deeper DC in the fore feet than the hinds.  A bit of a jackass question but would I use the same 'formula' for small ponies? Enjoying all this information.

Regards Sam

 

DrDeb
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 Posted: Tue Apr 13th, 2010 10:32 am
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Sam, notice it's not the absolute thickness of the DC that is of interest, but rather the thickness of the DC compared to the weight of the animal that we would be interested in.

This is the same relationship that we focus on when looking at bone-tendon circumference or hoof width (remember the thread from last winter when we had people here participating enthusiastically on that?). It is the ratio between B-T or hoof width (and now DC thickness) vs. weight that is of interest. We want to know how much DC thickness the animal has per thousand pounds of weight or per kilo.

So obviously then it would not matter whether you had a miniature or a Belgian draft. Except in one thing: as with B-T and hoof width, I will predict to you that we are going to find the same thing with DC thickness, i.e. that smaller horses have thicker DC's relative to their weight, and that larger horses have thinner, again relative to their weight.

That's my prediction, based on the fact that that's the way it works for B-T and HW. But! That's the beauty of doing scientific studies: we might find out that I am wrong in this -- that massive weight so greatly stimulates the cells that produce DC tissue that they do, in fact, produce so much of it that it goes up just as the horse's weight goes up. We'll see! -- Dr. Deb

minimitts
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 Posted: Wed Apr 14th, 2010 01:31 pm
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Hi Dr Deb,

I noticed looking at the Nevada hoof that it does not appear that the heel tubules are more upright than the toe tubules.  I recently attended a webinar with Brian Hampson, PhD candidate with Dr Chris Pollitt from the University of Queensland, who have both been studying the brumby hoof for the last 3 years.  Their data presents that the average toe angle of the desert brumby is 55 degrees, the average heel angle is 44 degrees. 

Perhaps I'm a dolt and have overlooked something, but I've been looking for research reflecting a higher heel angle of a "normal" hoof ~  If you have time, could you point me in the direction? 

Thanks for your time ~christina

DrDeb
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 Posted: Wed Apr 14th, 2010 08:28 pm
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No, Christina, you are not a dolt. There is a difference between studying the biomechanical model -- which is what the hoof-cone is -- and the real measured angles of feet.

An average for a population may tell you a number that not one single horse in that population actually presents. An average is computed from a range of actual measurements. Some of the Brumbies, and some Mustangs, do have heel tubule angles as steep or slightly steeper than the toe angle. Some have heels that are as run-under as you might find in any domestic barn. What are we to make of this reality?

The hoof-cone model is there to clarify for us what the biomechanics and especially the physics of hoof growth and pressures upon the capsule are. And what it tells us is what a hoof capsule would look like if the heels absolutely had no collapse in them at all.

We then look at whatever foot walks up to us and, having studied the model, are enabled to "see" how much collapse there actually is. Whether this needs to be addressed is quite another question, and so is whether having "X" amount of heel collapse is the optimal thing for the horse kept under whatever conditions it finds itself.

Many farriers have had trouble with this whole idea -- i.e. that you can learn very valuable things from a biomechanical model, things that you can carry into daily practice. Instead, what many people try to do is FORCE the model onto the horse. You cannot, of course, do this. What the model does, at base, is teach us that moving the heels back, encouraging the 'back of the foot' to grow, is always desirable, no matter the conditions or type of horse. -- Dr. Deb

Charlotte
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 Posted: Wed Apr 14th, 2010 10:14 pm
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Thanks for chromium info Pauline, much appreciated.

DrDeb
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 Posted: Thu Apr 15th, 2010 06:29 am
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Everybody -- Just wanted to poke in here to say we had a second go at having boots on Ollie's hind feet this afternoon. As I mentioned, he spent more than an hour the first time really working at trying to kick or stomp those boots off. What I didn't mention was that, as soon as I saw that he had realized that approach was going to be of absolutely no avail, and when I saw that he had resolved himself to take the responsibility for wearing them -- I say as soon as that occurred -- I took them off.

This is crucial, a core principle of training: "release" is great but it is release that occurs at the right time that gets the idea across to the horse, so that he learns it and accepts right down in his guts that this is just how it is going to be -- nothing bad will be allowed to happen to him -- if I should ask him to wear them.

I let one day go by in order to just leave him alone to think about it.

Then I came back today and rode him without any boots. At the end of the schooling session, I turned him loose in the indoor hall, with not even a halter on him. I went and got the boots. I walked up to him and let him smell them so he knew exactly what they were. Then I walked around behind him, asked him to pick up each hind foot in turn, and put the boots on him. Then I stood there petting him a little while. Then I asked him to go ahead and "leave", i.e. move away from me, at walk, "trot" (pace in Ollie's case), gait, and canter.

Not a single protest, not so much as a tail-swish, complete relaxation and equanimity the entire time, and 100% compliance with whatever I asked, just as in the preceding schooling ride.

This is what it means to get a horse to completely let go of his own ideas about something, and accept instead our idea. My idea about the boots is now also Ollie's idea. This is how you train but also maintain the friendship between you, or we could call that the horse's enthusiasm for being around you.

As soon this afternoon as Ollie had run through all gaits, both directions -- which took all of about five minutes -- I took the boots off again. Now I shall be able to put them on (or take them off) anytime I wish until my animal dies, and now can begin riding him with them on the hind feet, so as to report any differences that they may make in the "feel", especially during "up" transitions. -- Dr. Deb


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