[near horse]

Hey Mitch,

I think that outside of the whole draft buffer discussion here, one would/should change hitch length of the springtooth based on soil – newly plowed vs fall plowed. I would want to get a little lift (hook short) in that looser ground because dredging the springtooth through the soil is a pretty good load if it’s dragging dirt (seen it and done it).

That said, the erratic or changing draft of the springtooth on the fall ground is where I would imagine the spring buffer to work – levelling those peak drafts. Is that right or am I screwed up again?

Noteworthy – in the TB vs Draft horse comparison while both had similar peak force-speed , the draft achieved it at 2 m/s (~ 4.5 mph) vs 5m/s (~ 11mph) and the experimental treadmill couldn’t be set any slower than 2 m/s. Perhaps the benefit of the draft animal is the force generated at low speeds – much more practical for farm work. Ever run a tractor throught the field at 7 mph or more? Pretty rough stuff.

[near horse]

I know this paper might be getting away from the mechanics of draft but is worth a look. It kind of addresses what I was saying earlier about how human selection for specific traits may have created a wide range of physiological attributes in differing horse breeds. Plus, I like their treadmill/draft setup! They are attached to a “load” in this paper.

Force, speed, and oxygen consumption
in Thoroughbred and draft horses
U. SILKE BIRLENBACH POTARD,1 DAVID E. LEITH,2 AND M. ROGER FEDDE1

[near horse]

Hi Andy,

From the paper (actually in the abstract)

The estimated total mechanical work
(WTOT=WINT+WEXT) increased with speed, while metabolic
work (C) remained rather constant. As a consequence, the
‘apparent efficiency’ (effAPP=WTOT/C) increased from
10 % (walking) to over 100 % (galloping)

AND LATER ON (in the discussion)

…. the
value of C during walking is lower than that reported by Hoyt
and Taylor (1981). This is because the subtraction of basal
(standing) metabolic rate from the metabolic measurements, as
applied here, has a greater effect at low speeds than at higher
speeds (for a review of different techniques for calculating C,
see Full, 1991).

My point is that some of these numbers can be misleading.

Another interesting point is when isolationg the vertical, horizontal and lateral displacements as speed increased (Fig 5), it looks like there is an increase in vertical displacement (likely the change of gait) but no change in the horizontal displacement (stride length). That doesn’t make sense to me so I must be reading it wrong. Help me out here. OOPS – it’s displacement of the “center of body mass” – now I get it.

[near horse]

Hey Robert,

I just noticed this post today – sorry. I don’t have any pics from Pomeroy (or Colfax for that matter). What day was Kristi there and did she bring a team to Pomeroy? That might help me remember better. I did get to meet FarmerKitty and her family, though. Nice folks.

Man, don’t sell those longears short! There were a lot of them doing good work there. Most of the plowing events I ‘ve been to, have a big mule hitch either a 6 or 8 (greys) pulling a 2 or 3 bottom owned by John Obermeyer from Davenport, WA. Nice unit.

[near horse]

There are some sulkies setup with out a tongue – in fact some guys out here like them better w/o a tongue they say they’re not as “tippy”. Does there appear to be a rod linking the front furrow wheel to the rear furrow wheel? That is usually a sign that it used a tongue.

As Marshall said, a picture would really help.

[near horse]

I should mention that some of the news I’ve heard regarding the Madras sale this last weekend was for some with deep pockets – example a #9 high gear mower refurbished went for $4000. Yep, $4000. Ouch.

[near horse]

Interestingly, the authors also indicate that the shoulders of draft horses contain 4.5% of the total muscle, while those of race horses contain only 3.6%.

I think this may also point out that while “a horse is horse of course of course ….” the desired output from a draft vs a racehorse are miles apart and, I assume, selection has been directed toward maximizing traits that support the desired output – speed over a few minute mile and 1/4 or so in racehorses or a burst of power to overcome the inertia of a given load AND the stamina to keep that load moving – again and again in the working draft animal.

Besides distribution of muscle mass I wonder if there is a difference in the proportions of slow and fast twitch muscle fibers between the 2 groups – perhaps in the main muscle groups involved in locomotion. Likely someone has looked at that.

A neat aspect of animal power over the tractor is the subtle increase in power one can coax out of a team – enough to get through the wet muddy spot but not so much as to “spin the tires” and get ‘er stuck – like a tractor can.

At the plowing event this last weekend a fella was pulling some spring tooth harrow over plowed ground w/ 4 abreast on a forecart. The way he was setup the harrow was dredging soil pretty bad – you could barely see any part of the back of the spring tines so much earth had built up. So much that he couldn’t do anything to remove it on the spot. He decided to turn towards the unplowed ground and get off the soft stuff, perhaps dropping some of the soil as he crossed the plowed furrow. Unfortunately he had stopped out in the plowed ground before making this decision and therefore needed to get his team to start this load from a dead stop. Needless to say it was a real bear but those horses dug in, swung a little to one side and then the other and got that booger moving and over to solid ground. The ground they had pulled across and dug out on etc looked almost the same as the surrounding area. I believe that if a similar situation happened with a tractor there would at least be some serious wheel ruts left behind that would need some fixing. Not so with these horses.

Oh by the way, nice work Tim and Andy – And what does a biomechanic have in his rollaway toolchest?

[near horse]

I agree Andy and also think that we are interested more in power rather than speed. Also, my understanding was that because “resting metabolic rate” was relatively constant regardless of activity level, it would therefore makeup a larger portion of overall energy expenditure for walking over galloping. That would make a lower energy activity “appear” to be inefficient – maybe not the best word to describe it. At least that’s how I understood the article (good choice BTW!).

[near horse]

Hey Andy,

Do you have more of the citation for that paper? Where (which journal) published in … NEVER MIND – J. of Exp Bio. As I mentioned in a different thread somewhere on DAP, there was a paper back in the early 80’s called “Why Horses Change Gait” – had a nice graph of speed vs energy expended. As horses increased their speed, they could only reach a certain threshold before increased energy expenditure gave no increase in speed. Changing gait, say from a walk to a trot, allowed the increased speed for a significantly lower energy expenditure – kind of the “point of diminishing returns” concept.

[near horse]

First, thanks for your supportive words – all of you. I guess sometimes I wonder if I’m even on the same page as everyone else but then there’s that glimmer of something that makes me want to speak up.

So, I do appreciate Andy’s “preloaded spring” which I interpret to mean you have compressed the spring to one degree or another and the buffering effect would come from any force large enough to relieve some of the preload (allowing spring to extend towards its “normal position”). This is opposed to the alternative which is a spring in its “ready or normal state” (not compressed) which is stretched beyond the normal state when placed under a load. How do those 2 systems differ? Is it just easier to calibrate as well as have multiple settings from the preloaded spring or is there something more?

Regarding the tendon, ligament, muscle thing – I’m pretty positive that only muscle tissue has the ability to contract. BUT those muscles can stretch ligaments or put them under tension so that there is some energy stored there momentarily. For example fast runners, including horses have interesting combinations of muscles, tendons and ligaments that provide them the ability to run fast. If you’ve ever watched a cheetah or a cat run, the flexible spine forms an arch shape as the hind limbs move forward (way forward on cheetahs etc) – this is achieved through contraction of various muscles (perhaps abdominals). Then as the hind legs hit the ground and propel the animal forward, the back muscles rapidly contract shortening the back but extending the underside (reaching out with the fronts). In addition, when the spine was originally arched, a ligament or series of ligaments along the back were stretched (kind of like our spring). The energy “stored” up in the ligament by virtue of its being under tension is released as those back muscles contract – this system is pretty similar in horses although they don’t have as much spinal flex as cats.

Man I better go to bed now.

[near horse]

Isn’t the line of draft in the picture from blue80 way off? The traces are essentially parallel to the ground = zero lift on what ever the load was. Is that right?

Also, here’s food for thought (or maybe the obvious) – when a team digs out on a heavy load and the front feet come off the ground, could there be some small advantage gained by the rotational motion of their body thru the collar – Hang with me yet. Imagine the hind legs as a stationary end of a straight line (the horse body) and the front end being the moving end (like the hand on a clock). As the rear legs dig in and drop the hips, the front end gets a little elevation and as the front comes down (and the horse extends into the collar) the “rotational” motion of the body around the fixed point (rear legs) might provide a little extra burst to start the load moving.

Or for you physics purists – it’s a torque with the horse’s body being the moment arm.

[near horse]

I know I’m on the fringe in this discussion and this could be way off base but could the head bobbing be more of a response to a changing enter of gravity (or balance point) as they walk – factor in a draft load and …. The reason I say this is I know some birds like geese and ducks extend or retract their necks to alter the center of gravity for take offs and landings.

Again, this might be splitting hairs, but I don’t remember tendons and ligaments being able to contract – only muscles. And muscles can only shorten (contract) or relax – no lengthening per se. That said, the biomechanics of how the muscle works a joint based on its point of attachment etc is how the work gets done. It is really incredible the series of levers (muscle/joint combinations) that work in unison to provide motion.

I think some of what we see in changes in movement based on load (or speed) is a result of utilizing additional muscle/joint combos as needed. For example, at a basic unloaded walk, it is primarily leg muscles doing the “work”. But when the load is increased I think some of the core musculature (particularly the back or back strap or tenderloin – your choice) comes into play in addition to the driving leg muscles. While not the same thing, that is how most quadripedal mammals run fast. Drive off the rear legs, extend the front through contracting the back muscles, and reach forward and anchor the front with the front limbs – repeat.

Sorry if I take us off topic – perhaps I should just listen 🙂

[near horse]

I’m guilty too – I use a tractor but try to find ways not to. Going to all horse power is a little more involved than just switching the power source. Some jobs require a team, others 4 horses (or more) and more people. While you can keep more horses it can be a challenge to find more willing help at the necessary time. So in comes the tractor.

Ed, I wouldn’t beat mtself up over using a tractor UNLESS you traded in your horses for it!! Take it easy and enjoy the things you can do with them.

[near horse]

Is there anything we can say about the relationship on your graph between draft and speed? This might be “the chicken or the egg” type of question but does one seem dependent on the other? Were the animals allowed to move out at the speed of their choice or were they held to a certain range (like only walking)? I know the speed and draft measurements were taken very close together in time but were they actually simultaneous? It just seems that ground speed should end up being dependent on draft – higher draft we get a lower speed. That looks like the case in some instances while in others – not so. Or is it a constantly shifting relationship in which higher draft results in a momentary slow down which in turn causes the animals to increase pull which then increases ground speed momentarily …..

Oh the challenges of applying physical concepts to biological systems! Good work Tim.

[near horse]

In thinking about this more, if we are using the term “buffer” to mean resistant to change, then I can agree that certain devices (like the nylon harness or spring) will buffer the draft on an animal or team.

One other question regarding one of your graphs Tim. Why did using nylon harness on the steel wheeled units result in higher average horizontal draft for both oxen and horses? Didn’t the nylon harness give lower values for the rubber-tired wagons?

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