Monday, November 21, 2011

Laminitis: Hoof wall growth

The first thing you need to know about the hoof wall is that it is actually composed of three different sections:

  • the distal hoof wall/pigmented wall/stratum medium, 
  • the water line/unpigmented wall/stratum internum
  • the white line/epidermal lamellae
To understand hoof wall growth we also need to focus on the lamellae, of which there are four types:
  • Primary Epidermal Lamellae (PEL)
  • Secondary Epidermal Lamellae (SEL)
  • Primary Dermal Lamellae (PDL)
  • Secondary Dermal Lamellae (SDL)
The lamellae from the epidermis (outside of the hoof) interlock with the lamellae from the dermis (inside of the hoof) by means of a basement membrane. "The basement membrane is a thin, unbroken sheet of extracellular material, partitioning the dermis from the epidermis (Pollitt)."

Each one of the SEL (the little fingers hanging off each PEL) is attached to the basement membrane by a hemidesmosome through anchoring filaments. Anchoring filaments are composed of a glycoprotein molecule called laminin-5 and a protein called BP-180.

Following along so far? Okay...

The coronet band is constantly creating new cells for the hoof wall, which means there needs to be a mechanism to move the already existing wall down towards the ground to make room for the new cells. To do that, lamellar remodeling enzymes called matrix metalloproteinases (MMPs) come through and pop the hemidesmosomes off the basement membrane (not all at once, mind you), tissue inhibitors called TIMPs then turn the MMPs off, and the loosened cells then move downward and reattach lower on the basement membrane by the anchoring filaments.

This process happens constantly in order to keep up with the growth from the coronet band. The MMPs, TIMPs, and anchoring filaments are always working in a very delicate balance to keep the hoof wall growing and replace material lost at ground level.

And that's hoof wall growth in a nutshell.

Upon further examination, Bowker's theory of hoof wall growth doesn't differ terribly from this, he just posits that the PELs actually contribute cells to the stratum internum to increase hoof wall thickness closer to the ground. For the purpose of understanding laminitis that isn't terribly important (just interesting).

All the info in this post I learned from reading the work of Chris Pollitt, I'll provide links later on. You'll notice that I've made a few words a little more "obvious." Try to remember those, they'll be important later.

11 comments:

  1. Thanks for the info. I'm interested in this because of Dusty's bouts of laminitis/founder. I feel that I know the basic gist of how things work but by putting it all in one spot the research you've done will help me better understand what's going on with her foot/hoof walls. I've never been much good at science and didn't pay enough attention in class(many years ago) hope I can still grasp the concept of learning something new at this stage of the game.

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  2. I'm visiting new blogs today for the first time, so i also thought id wish you a Happy Thanksgiving to you and your readers. And i hope that the day is spent generating positive memories for years to come. Richard from Amish Stories.

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  3. You can always learn something new- in fact, it's good for your brain! My worst subjects were biology and chemistry, fortunately my husband has a PhD in biology, so when I get stumped I can just ask him to decipher for me. He's been very helpful!

    Amish Stories- happy Thanksgiving to you!

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  4. I learn SO much from your blog! Can I ask you a somewhat unrelated question? Miles is barefoot...one of the reasons my farrier wants him in shoes is because he says it would control the flare he gets on the outside of his front feet. Theoretically, is this something I could control myself between trimmings by using a rasp or one of those files with a fancy ergonomic grip? If this is the wrong place to ask I'm sorry...my email is sarah.szwejda@gmail.com if you would rather. Thanks!!

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  5. Thank you for saying that, I like to share the wealth (of knowledge).

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  6. Just thought I'd stop by and wish you and yours a Happy Thanksgiving.

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  7. Wow..So, in our case, that would make sense as to why Laz's hoof wall in his MOST damaged section (medial) has such a THICK wall and isn't growing OUT as much as it's growing thick. The hoof want's to heal where it rotated and had missing stretched laminae. I think??? LOL So..how does sole grow? Or from where?

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  8. Thanks GHM :)

    Kristen in Laz's case I think the basement membrane might have been damaged. More info forthcoming...

    Sole grows from the papillae under the coffin bone. According to Bowker it also grows from the bars but IMO that research is flawed.

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  9. Great equestrian blog! Why not come along and post this blog at hay-net.co.uk? This is the UK's No1 Equine Social Blogging Network so come and meet other equestrian bloggers from all over the world!

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  10. This theory is old....

    The growth of the hoof does not go only to the coronary band.

    The lamina produces the inner wall, while it does not work like velcro!

    The theory of the velcro does not explain the metabolic flare, and does not explain the keratinization of the inner wall during a resection.

    the dermal papilla of a lamina produce the horn tubules and inter tubular horn.

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    1. I assume you're talking about Bowker's theory here. As I read it, Bowker's theory says that the dermal papilla contribute cells to the stratum internum and this increases the width of the hoof wall- the external hoof wall still originates at the coronet band. His theory does not negate the older theory of hoof wall growth, it's an addendum.

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