Starting draft

[Andy Carson]

H. Ortiz-Laurel and P.A. Cowell. “Power Output Measurement on Draught Horses”. Agricultural Engineering International: the CIGR Ejournal. Manuscript PM 07 001. Vol. IX. August, 2007.

Another fascinating read where the authors have studied draft forces on a 900 lb highland pony pulling various loads. Althought they tested a maximum pull of only 160 lbf, thier system allows them to measure both the verticle and the horizontal component of the developed force on each individual limb.

Some interesting conclusions from this study:

1. The forelegs of this horse carried greater weight at all draft loads, but the load was progressively transferred to the hind legs as draft increased

2. At low draft loads, the forelegs and the hind legs made nearly equal contributions to the propulsion force. At a draft load of 160 lbf the hind legs contributed 57% percent of the horizontal pull. Although they didn’t test higher loads, the curve of power vs load generated by the hind legs looks very linear and is a long way from any plateau. The power vs load for the front legs, though, seems to reach a plateau near the maximum tested.

3. The difference between the power developed by the hind legs and the power developed by the front legs grows as the load is increased.

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 indicates that the front limbs are very important for something, even though they seem (on the surface) to be less important as draft increases. I think this supports the idea that while the majority of the power generated by horses under heavy loads is generated by the hind legs, the load that can be maintained at a normal walk (rather than with periodic double hind leg thrusts) is limited by the ability of the front limbs to maintain foward momentum during the time between single hind leg thrusts. That makes me think… Tim, on the graphs you generated for starting a load, were the horses starting with a “double leg thrust” or simply “walking off”?

[Tim Harrigan]

Countymouse;17639 wrote:

… Tim, on the graphs you generated for starting a load, were the horses starting with a “double leg thrust” or simply “walking off”?

I don’t remember watching for that specifically. My guess is with that load they used both legs, at least for the first stride.

[Gabe Ayers]

People, this is some cool stuff….. way over my head boys. I love it though – so interesting to read the information.

Yet I kinda agree with Mitch about the mystery of their biological existence and potentials, as maybe being the greatest power.

The culture of making this life force to be useful is made even more fascinating by your discussions here.

The art and science of animal power. Carry on….please.

Awesome. Thanks!

~

[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?

[Andy Carson]

Thanks for the words of encouragement. I am certainly not an expert, but I find these types of discussions very fun and am glad others find them interesting as well. This site has really been an incredible source of both practical information and inspiration and I am honored to be able to contribute to the community a little in a meaningful way. This is a field where the “art” probably matters more than the “science”, but a little science can’t hurt. I remember Carl’s thread about how he moved the large oak logs up a steep hill and how he used simple, but cleverly designed stratagees to give the animals advantage and make the job more efficient for the horses. Perhaps with a more complete understanding of the efficiencies and inefficiencies of animals, we, as a community, can find clever ways to overcome limitations and improve the capacity of the animals to do work.

[Author]

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