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size of horse that is healthy biomechanically
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marji
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 Posted: Wed Feb 22nd, 2012 03:38 am
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Hi, I am hoping someone can point me in the right direction. I am looking for any references (books, forums, etc.) where Dr. Deb discusses the relationship of size/height of horses that is healthy biomechanically for the equine species. Any assistance will be greatly appreciated.

DrDeb
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 Posted: Wed Feb 22nd, 2012 07:27 am
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Marji, I have discussed and presented data relating to optimum size in riding horses -- about three years ago now, in Equus Magazine. The information appeared in an article near the beginning of the current conformation-biomechanics series.

I would also like to ask, though, why you are asking. Is this relating to a school science project or a 4H project, perhaps?

Also: what, exactly, do you mean by 'healthy biomechanically'? How do you conceive that the horse's height or weight relates to his health, or in other words, I need you to clarify more about what you would like to know. -- Dr. Deb

marji
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 Posted: Wed Feb 22nd, 2012 10:27 am
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Hi Dr Deb, Sorry I know that you are a very busy lady and was hoping that someone else could point me in the right direction without troubling you. It has been my observation over the years that sport/recreational dressage horses over 16.2 almost always break down with leg/hoof problems. Absolutely no scientific backup to this, excepting for the fact that I was once told that the first step in science is observation. Due to my observation of hundreds of horses in my clinics and the dressage, eventing and showjumping scenes over more years than I like to admit to, I have given it as my opinion that horses over 16.2 are not likely to be healthy biomechanically. I have been challenged and would like to know if there is any scientific evidence to back up my opinion. On the other hand, scientific evidence might prove me wrong. I am fully aware that correct husbandry and training which ensures that the horse has good posture, etc has a bearing on this, but as I am committed to breeding sport/classical dressage horses which are sound in mind and body I have made one of my breed criteria that the average is 16.00 hh. I suspect that the optimum height would be even less than this for bone density/height, but as I am breeding horses which are competing successfully both internationally and nationally I think that they would be hard pushed at less than 15.3 hh. Hope this is not too long winded. It is my first time on a forum. Best wishes, Marji

DrDeb
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 Posted: Wed Feb 22nd, 2012 07:19 pm
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Marji, you are very welcome to be here, and your question and post are both just fine. And do not worry about being a 'bother' to me: this is a somewhat unusual Forum in that, while discussion of a polite nature is encouraged, this is in fact my online international classroom, so that discussions are actually classroom discussions with me as moderator.

We do maintain certain rules, premier among which is that horseback riding/horsemanship teachers cannot so much as be named unless they are on our approved list, and even those who can be named can only be talked about in positive terms. This keeps discussions totally away from "personalities" and instead focused on content. In other words, if someone goes to a horsemanship clinic or "school" and they see something they either don't understand or they think they don't approve of, instead of writing in here and saying 'Jack so-and-so did this and I'm all in a huff', they are to write in and say, 'I observed someone do so-and-so with a horse and this was what I thought the effect was and this is what I thought the purpose of it was, but I don't understand it.'

Of course, YOU will not have any trouble here at all, Marji, because we are fans of Nuno Oliveira, I am friends with several other old Nuno students besides yourself, and I admire and approve of Nuno's teaching and approach. Further, I know several of your own students, one quite well, and I see from this that they learn the same correct techniques and concepts that were taught not only by Nuno but by my own teachers as well, who were Ray Hunt and Tom Dorrance. Despite the difference in 'hats', there are many commonalities and we seek to find the commonalities which define the High School and classicism in its broad sense, so that, as Jesus said, 'he who is not against us is for us.'

Now as to your question, you will find that if you get ahold of the Equus Magazine back issues I previously mentioned -- Alex has them I believe, or else you can order them from the publisher -- you will find that, far from there being 'absolutely no science' to back up the idea that the bigger a horse is the less sound he is likely to be, the science backs you up 100%. The very concept is basic, and derives directly from concepts taught in any high school in the Physics 101 course, i.e. the interaction of mass and energy and the principles that underpin the structural engineering of buildings. You cannot safely put a heavy roof, or one that's going to get a big snow load in winter, on skinny little pylons; and the bigger the building gets, the bigger the pylons must also get -- but -- here's the key -- NOT in the proportion you might expect. The relationship is not geometric but (more or less) logarithmic, meaning that if you double the weight of the building the pylons have to be made more than double thick.

Further, it is just as true of horses as of bricks or boxes, that if you double the unit dimension, you much more than double the volume (which translates directly to the mass). So, for example, if you have a cube that measures 2 ft. on edge, it has an internal volume of 2 X 2 X 2 = 8 cu. ft. But if you double that cube's unit dimension to 4 ft., it will then have an internal volume of 4 X 4 X 4 = 64 cu. ft., which is not twice as great but eight times as great. And it does not matter whether you fill that box with lead, styrofoam, or flesh-and-blood, the amount that it weighs will also go from 8 units of weight to 64 units of weight, and eightfold increase.

It does not matter, either, whether the 'box' being filled is irregular in shape. So, the practical application of this to horse breeding and training is that if you have a wee pony that stands 9 hands in height, he will weigh 300 lbs. And if you double his height to 18 hands, our formula predicts that he will then weigh 300 X 8 = 2400 lbs., which is what big draft horses really do weigh.

When you go read the advertisements published by the common warmblood breeder, they will trumpet that their horse sports "9 1/2 inches of bone", which means that the animal tapes 9.5 inches at the standard point just below the knee in the forelimb. This same horse will stand 17 hh and weigh 1650 lbs. Data developed from well-known height vs. bone tables (Germany and the U.S., broad spectrum of breeds, sample size of over 5,000 animals) tells us that to remain sound over years of use, a riding horse needs to have 8 inches of 'bone' per 1,000 lbs. of weight. The same data also tells us that a racehorse (race horses are not the same physical type as riding horses) can get away with as little as 7 inches of 'bone' per 1,000 lbs. of weight. On this basis, does the advertised WB meet minimum criteria? Not at all: for a 1650-lb. horse (i.e. ~ 800 kg) would optimally have 8/1000 ~ x/1650 = 13.2 inches of 'bone', and would at minimum need to have 7/1000 ~ x/1650 = 11.5 inches.

All this becomes even more stark when it is realized that the same data tables, which include wild equines -- the Przewalski horse and the zebra most physically similar to the horse, the Bontequagga -- have not 7, not 8, but FOURTEEN inches of bone per 1,000 lbs. of mass. This reduction in substance of nearly 50% has occurred not only in horses as a side effect of their having been brought into domestication, but also with all the other mammal species that have been domesticated, i.e. sheep, goats, cattle, and the 'primitive' or undifferentiated domestic dog.

I have hereby given you a simple formula which you can trot right out to your own barn and apply. All you need to know is the weight of the horse to the nearest 50 lbs., and the taped circumference of the forelimb at the standard point just below the knee. As you breed Lippies and other horses suitable for classical horsemanship, I doubt you'll find many deficiencies but it sure doesn't hurt to look and I'll bet you'd enjoy doing it.

If you want more information, or more to share with your customers and students, besides the Equus Magazine articles, you can go over to our bookstore and obtain a copy of the "Conformation Biomechanics" 4-DVD set. In that program I take you to my barn and my own horse Oliver, using him as the living example; and then we go into my laboratory, where we can directly study the skeleton, which is the underpinning for all of this. You will find much information in there that will explain, or else confirm, what Nuno taught, as well as directly addressing this particular question.

Please feel free to write back at any time if you have further ideas and observations. -- Dr. Deb

Dorothy
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 Posted: Sun Mar 4th, 2012 09:23 am
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Dr Deb, how much truth is there in the belief that Arabs have denser and therefore stronger bone than other breeds? Is some bone actually stronger than other bone, when comparing, for example, cannon bones? or is all bone the same?

thank you, Dorothy

DrDeb
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 Posted: Mon Mar 5th, 2012 08:14 am
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Dorothy -- Did you miss this entire topic when it was discussed here two years ago? The discussion was thorough and I set it all down in writing, as this is a question I positively got so sick of hearing that I actually designed and executed an empirical study of it twenty years ago when I was employed at the U.S. National Museum of Natural History/Smithsonian Institution. THERE IS NO SUCH THING AS 'DENSE' BONE IN ANY HEALTHY MAMMAL. But you need to read the whole thing to understand the statement.

You can find the discussion by doing a Google advanced search, or else, even better if you want to see the final results, get the Equus Magazine back issue where it was printed. This would be early in the new conformation series, since this is a very basic issue, i.e. relating to the question of whether large horses are congenitally unsound, or what the engineering properties of large vs. small horses are.

Use the following keywords when you do your Google search: density, bone density, bone-tendon circumference. And, remember to dub in our Forum address at the bottom of the Google form so as to limit the search to just this board: http://esiforum.mywowbb.com

 

Dorothy
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 Posted: Mon Mar 5th, 2012 12:28 pm
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Thank you, I must have missed the discussion, or more likely, forgotten that I have read it amongst the wealth of information. I apologise for asking the question again!

I shall search the previous threads...

Dorothy

Blaine
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 Posted: Wed Mar 7th, 2012 10:03 am
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The Equus article was really a wonderful find for me personally as I am above average in the height department and am always being encouraged to trade in my 15.2 hand mare for something in the 16-17 hand department. The article really helped me to see that that I didn't want to deal with lameness issues just so my feet didn't dangle so far below my horse's belly!
 

marji
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 Posted: Fri Dec 28th, 2012 05:47 am
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Hi DrDeb, Would like to have confidential discussion.  Email - yardah@westnet.com.au

In the meantime, have a couple further questions in regard to the discussion.  1. At what age should the measure of bone/tendon.  2. Do you have a diagramme of the place below the knee.

Happy Christmas & 2013 happiness. regards, marji

DrDeb
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 Posted: Fri Dec 28th, 2012 06:09 am
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Sorry, Marji, I don't have confidential discussions on horsemanship topics. If you aren't willing to air whatever query you have in this Forum, or else in front of the attending public at one of my live seminars or horsemanship rides, then you'll have to go elsewhere for advice. We don't have secrets here; we don't have cliques; we don't have 'teacher's pets' or special insiders; we are all equal.

As to your two other queries -- Marji, you still haven't done as you were told -- i.e. to go get the back issues of Equus Magazine where this is discussed, or else purchase "Principles of Conformation Analysis" from them (I don't sell that book, even though it is authored by me). Please do the homework -- then come back with further questions. -- Dr. Deb

marji
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 Posted: Fri Dec 28th, 2012 08:16 am
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Hi Dr. Deb, Unfortunately you seemed to make assumptions on why I wanted to speak with you.  The confidential discussions had nothing to do with horsemanship topics.  Equal, special insider or anything like this. 
Any horsemanship discussion I am always up for discussion in the public. Okay.

Regarding I have read up your Principles of Conformation Analysis Volume 1, Page 79, Figure 34.  I guess I should have asked a little more clearly about my question.  So the measure taken. I was making the measure immediately below the actual lower part of the knee.  The part that I measured was the larger in regard to the rest of the leg.  i.e. the measurements were smaller further down the leg.
 
In regard to the age when the bone/tendon measurement can be answered.  I could not find anything in relation to that. 
I do remember in one of your articles talks (Growth Plates) about the fact that the knee is one of the earlier development part of the horse compared to the lateness of vertebral "closure" is much later. So, in regard to this article, would it mean that the bone/density measurement should be best done after 2.5 years.

i.e. extract from your article - Growth Plates.Makes my assumption that the pointed that I am looking at is the Bottom section of the the radius-ulna? i.e.#6 below.

5. Small bones of knee - top & bottom on each, between 1.5 and 2.5 yrs.
6. Bottom of radius-ulna - between 2 and 2.5 yrs.

Best wishes, Marji

DrDeb
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 Posted: Fri Dec 28th, 2012 09:38 pm
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Marji, OK, if you want or need to contact me about something else, all you have to do is write an EMail to office@equinestudies.org.

As to your queries, I am delighted to see by your last transmission that you have done some homework. The reason that the standard point for measurement of cannon-tendon circumference is just below the horse's knee is that, in normal, healthy, nonpathological horses this is the narrowest point in the lower part of the limb. In other words, what you are being asked to look at is the "worst case scenario", because greater substance anywhere else in the leg is meaningless with respect to the limb's ability to uphold the mass -- just as having a narrow spot in the posts that hold up the roof of a barn would be an engineer's focus of concern. The architectural analogy fails, however, to this extent -- that the narrowest point in a horse's leg is not likely to be the point at which the structure fails, but rather is that area least covered by flesh, and thus the closest measure we can get in the living animal of the actual "bone substance".

 As to age at which the measurement is taken -- you are here, I think, confusing the common commercial practices with the actual developmental sequence. Horse-traders, in other words, have a vested interest in being able to tell potential buyers of riding horses that the animals they have for sale have "big bone" or "substantial bone" -- that is, anyway, if they have clientele that is at least somewhat knowledgeable, that would be what the clientele would be looking for. But sellers universally neglect to relate the amount of bone to the mass of the animal, which is the only thing that really counts.

Anyone, such as yourself, who has years of experience with breeding horses, knows that foals have what "appear" to be skinny little legs -- skinny, that is, in comparison to their sires and dams and older brothers and sisters. This is because the circumferential size of bones of the limbs, that provide support for the mass above, is designed by nature to increase by the very physical laws which the engineer uses to design a barn which will stand up to the load of its roof. This law is:

"The weight-bearing ability of a supporting member is proportional to its cross-sectional area".

We cannot measure the cross-sectional area of any bone in a living horse or foal, because to do so we would have to saw one of its legs off. Happily, however, the formula for the area of the cross-section of a cylinder (A = pi X r X r) is easily convertible to that for the circumference of a cylinder (C = 2 X pi X r), thus enabling us to simply use a tape measure AND (mind this!) a scale.

In other words, for a bone-tendon circumference measurement to have any meaning at all, it MUST be related to the weight of the animal. And this relationship will be the same no matter whether the animal is a weanling, a yearling, a two year old, or a mature horse. The weight you need to use would be the pasture-fit weight of the animal (i.e. not obese), plus or minus 50 lbs.

This is the true meaning of "substantialness" -- that the animal's limbs are stout enough to bear its weight. The relationship for a riding horse would be 8 inches of bone-tendon circumference measured at the standard point just below the knee for every 1,000 lbs. of weight. Thus for a weanling weighing 350 lbs., ideally one would find 2.8 inches of B-T circumference, using the following handy formula:

8 in. circumference/1,000 lbs. = x circumference/350 lbs.

Thus, 8 X 350 = 2800, then divide by 1,000 to get 2.8 inches as the value of "x".

Alternatively for a mature horse weighing 1200 lbs., you would multiply 8 X 1200 = 9,600 and divide by 1,000 to get 9.6 inches.

I regard the domestic species average to be the minimum for riding horses. This average is 7.5 inches of bone/1,000 lbs. weight. This then yields the minimum I would consider acceptable, as below:

7.5 in. circumference/1,000 lbs. = x circumference/350 lbs.

2.6 inches of B-T circumference for the weanling;

7.5 X 1200 = 9 inches of "bone" for the mature horse example.

Note that this formula is "handy" because it does not require you to mess with calculating by logarithmic functions. In point of actual fact, the relationship between mass and BT circumference in not only horses, but all mammals, is not geometric or "straight line" as this handy formula implies, but logarithmic. We can work the "handy" formula for horses more or less usefully because riding horses -- for which these formulas would be put most into use -- weigh between about 800 and 1500 lbs., a relatively small range of size. However, pony breeders and draft horse breeders whose horses lie outside this range should note that the formula works less perfectly for them. In the case of the ponies, it is too severe -- most horses that weigh below 800 lbs. have plenty of bone, almost as much as their wild ancestors, averaging in the 10 inch per 1,000 lb. range.

For horses over 1500 lbs., the formula is too lenient; these horses in actual fact need MORE than 8 inches per thousand pounds if a person would be so foolish as to have the idea that such a ponderous and otherwise unadapted horse should be ridden. Unfortunately today this is much in vogue. The average B-T circumference in horses over 1500 lbs. is under 7 inches per 1,000 lbs. of weight, and as we look at horses above 1600 lbs. in weight it falls to only 5.5 inches. This makes these draft horses suitable for one thing, and one thing only -- drafting, i.e., work at a walk or slow trot; certainly not riding.

One can, of course, get the exceptional individual in any breed; but readers should remember that, by the formulas given here, a 2,000 lb. behemoth that some idiot intends to ride would need 16 inches of B-T circumference. The largest B-T ever recorded is just shy of 15 inches, and that was on a horse weighing over 2600 lbs., which is more than a bull rhinoceros. I leave it to you to work out what the B-T ratio was in this individual, whereas by contrast it is very common to find 700-lb. ponies with 8-inch B-T. I repeat: without weight data to go with the B-T, no buyer should pay the slightest attention to any seller's proud declaration of how much "bone" the prospect they have for sale has. -- Dr. Deb

californianinkansas
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 Posted: Mon Dec 31st, 2012 04:23 pm
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Dr. Deb and Ms. Marji,
Good morning. Thank you both for this posting. Reading this information one more time in a different format with slightly different wording finally enabled "the light to go on" in my head on this concept (I had to take Trigonometry twice as an undergrad before it "sunk in.").
Thank you, Dr. Deb, for your time and expertise.
Very Respectfully,
Amber


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