Friday Weird Science: Shearing Sheep on Slick Surfaces, a Scary Situation

Nov 09 2012 Published by under Friday Weird Science

Today's Friday Weird Science comes courtesy of Marc Abrahams of the IgNobel prizes who sent me this fabulous study. Because who doesn't love some sheep?

Shearing sheep is not an easy job. When I pictured sheep shearing, I always pictured someone leading in a sheep, and the sheep standing patiently while someone takes some clippers to it. Turns out, I was VERY wrong.

...and then boy, did I feel sheepish.

You see what I did there. I had to do it just ONCE! HONEST! Don't go away! I promise I won't do it again!!

Harvey et al. "An analysis of the forces required to drag sheep over various surfaces" Applied Ergonomics, 2002.

Shearing sheep is a tough job. Sheep look cuddly and sweet.

(Awwwww. Source)

But sheep can be STUBBORN. Especially when having to do things they aren't thrilled about doing, like, say, getting that nice, warm thick winter coat removed in the spring/summer.

So when shearers go to shear the sheep in the spring, they face a lot of resistance. You might think that this means the sheep go stiff-legged and refuse to budge. And yeah, they do that. So in order to get your sheep into proper shearing position, you need it belly-up.

Like this:


So to position the sheep, the shearers flip it on its back, and drag it by its front legs to the shearing area. Like so:

But sheep are heavy, and floors are rough. And so it's a LOT of work. So much so that sheep shearers have six times more back injuries than the average industry profession. So the authors of this study wanted to find out how to reduce the possibility of injury by varying up the floor surface.

The floor surfaces here are somewhat limited. It can't be too slick, you've got to be able to get purchase and drag a heavy sheep, but too rough, and it'll take too much force. In the end, the authors looked at five different kind of flooring:

1. Wood battens oriented parallel to the drag.
2. Wood battens oriented at right angles to the drag.
3. Plastic battens oriented parallel to the drag.
4. Plastic battens oriented at right angles to the drag.
5. Steel mesh.

They also looked at the angle, either on flat or at a 5.6 degree decline.

And then they took 8 experienced shearers, and 5 very long-suffering sheep, and tested them on the surfaces. For each surface they looked at the dragging force and the maximum vertical ground reaction to the shearer, to calculate how much work the shearer was doing and whether it varied as a result of surface. The physics of this ends up looking like this:

You've got the force exerted by the shearer, the weight of the sheep pulling down, and the friction of the flooring providing resistance, as well as the angle of the floor.

They also put together a biomechanical model:

What they found is that the best flooring is wooden planks, placed parallel to the sheep dragging direction. So the boards and the sheep are going the same way. The best angle was a downward one of 5.6 degrees. This not only is better than plastic or horizontal planks, it actually reduced the force required by 15%, which could be the difference between health and major back strain. Wire mesh (unsurprisingly, perhaps), was the worst, producing a massive 422 N of force, close to the maximum limit possible for a really fit man. The authors recommend switching to wooden boards.

But in the end, while this may have accomplished great things for the lower back health of the sheep mostly involved dragging sheep over different kinds of flooring. For science. And the next time you snuggle up in a wool sweater, think of those strong shearers, and those incredibly patient sheep.

Harvey JT, Culvenor J, Payne W, Cowley S, Lawrance M, Stuart D, & Williams R (2002). An analysis of the forces required to drag sheep over various surfaces. Applied ergonomics, 33 (6), 523-31 PMID: 12507336

9 responses so far

  • fusilier says:

    I have sent this link to My Beloved and Darling Wife, who will share this with spinners, knitters, and weavers the world over.

    applause, applause, applause

    James 2:24

  • Chemjobber says:

    "Applied Ergonomics" -- probably a journal that could do with more reading, really.

  • Christina Pikas says:

    May I invite you to the Maryland Sheep and Wool Festival, the first weekend in May? It's free and you can watch sheep shearing demonstrations. It's like a wrestling match - I had no idea! I sort of thought they would stand there and get trimmed but oh no. I think they did it over a tarp at the festival so that we could see and they could gather up the fleece.

    • Scicurious says:

      Ooooh, more importantly, you can invite me and I can buy LOADS of DELICIOUS SOFT SNUGGLY YARN!!!

    • Jim says:

      Or come to the Pennsylvania Farm Show for the "Sheep to shawl" competition in January 2013. As the name implies, teams take the wool off the sheep, card & spin it, then weave the yarn into a shawl - - all in a timed event. Then the shawls are auctioned. Great fun to watch, even on TV.

  • This makes my little spinner's heart happy. I wonder also about the ergonomics of the skirting table process, though.

  • Alex says:

    The thing about sheep "in the grease", so to speak, is that their fleece is full of lanolin. Sheep are generally shorn in warm weather, which means a certain amount of the natural lanolin in their coats is ready to smear off onto surfaces (such as floors).

    In many long-standing shearing sheds the floorboards are almost slick with grease, which assists with the dragging of sheep along the floor.

    I"m not particularly surprised that dragging a sheep along the grain of the floorboards is the most efficient and produces the least drag - anyone who ever slid along a wooden floor in their socks will tell you the same thing - slide along the grain, not across it.

    As for those who thought sheep would daintily trot in and stand still to be shorn: a sheep is a very stupid animal. It knows that being separated from its flock is a Bad Thing, so it will struggle and wriggle and do anything to remain with the flock. Once on its back, though, it generally calms down and allows the shearer to do his/her work. The look of relief on a sheep's face when the fleece is gone and it is sent back to the holding pen can be quite comical.

  • ryandake says:

    you know, i read the title of this post in my RSS feed and started laughing so hard i could barely click on it... Sci, you are a glorious and utterly unique addition to the species 🙂

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