GP or not GP, that is the question...

This was posted a couple of years ago on EC Hoof in response to a question about ground parallel pedal bones.


I trim to allow the horse to stand, land and move as naturally as it is able to at any given point in time. 'Naturally' is mainly what looks right to me but that relates back to the standard of 'good' conformation and movement I was taught decades ago - and which I see no reason to discard. 

I prefer to do the least possible and let the horse sort itself out - where it can - although sometimes I might trim quite intensively. 

It depends. 

I do take into account a horse's age and physical condition - especially joint adaptation / arthritis. There's no point in lowering a heel if the horse really can't or won't weight it. But I try to identify the reasons why it can't/ won't weight correctly and, if they are resolvable, address them. If they are not resolvable then the trim must aim for maximum comfort but (hopefully) not at the expense of vital functions. 

It's sometimes a tight rope walk.

The critical thing is to break the vicious circle of chronic pain, skeletal imbalance, muscle tension etc as quickly and as naturally as possible. The time frame, methods involved will all vary depending on the situation obviously.

I often don't get xrays - for practical reasons (cost, distance to clincs etc) - unless I really need to see inside the hoof. I work mostly on what I can see, feel and logically deduce from the hoof and from the way the horse stands and moves. But, sometimes I won't trim without them. And sometimes I wish I hadn't bothered because of the points John (Stewart) makes about the importance of angle etc.  

The points I am making about the ground parallel pedal bone are about whether it is just a theoretical plane from which to measure degrees of deviation. 

What is the acceptable deviation - John's 5-ish degrees, Pete Ramey's 1-3ish degrees, some farriers' 5-10+ degrees - or Strasser's 0-ish degrees? 

Why is it, as John says he observes in the UK, that it's ok to trim to GP on hind feet, but trim to as much as 10 degrees above that on the main weightbearing limbs? 

What are the implications, to the skeleton, of fore and hind pedal bones that are sitting at differential angles to the ground? 

Is this something which differs according to terrain? 

We know that hard terrain /high movement horses tend to have pedal bones carried higher in a more concave hoof capsule than soft terrain horses - and have thicker but more abraded (rolled) toe walls which look steeper than the thinner 'sharper' edged walls typical of soft terrain horses. 

Estimates of pedal bone orientation in these hard terrain hooves tend to come from populations of feral horses - as I understand it from x-rays of cadaver hooves or recumbent sedated horses - as it is very hard to x-ray a feral horse whilst upright.

What difference does a completely unweighted capsule make to how P3 appears to sit in the capsule in an x-ray? Can an artificial load on a cadaver hoof replicate natural loading forces? 

Strasser says that the cadaver feet of US mustangs she's seen have highly abraded toes but GP pedal bones. Current studies of Australian brumbies show a wide variation in dorsal wall angles - all steeper than 45 degrees but I don't know how these were measured or if x-rays were done and if so - how. Other feral populations like the ones here in NZ have more typical soft terrain hoof form. I have no idea about their angles.

I do agree that some horses can cope very well with a pedal bone that is quite forward of ground parallel - and that any pain and degeneration from that situation may be less problematic than the reverse situation of a too low heel with the back of the coffin joint being persistently stressed. 

The points I made about how stable P3 SHOULD be in a healthy hoof that is attached to a healthy properly functioning body - are not to suggest that I have a magic formula for restoring feet and bodies to that state. No-one does - and some horses will never have optimal feet because the opportunity to develop them has been lost forever. Some may well need a bit of extra height at the heel, ie the deal for them is that the potential for harm of an elevated palmar angle is less than the potential for harm of a GP pedal bone which is at risk of becoming negatively inclined on impact or persistently.

Which is pretty much the argument for shoes - the harm they do is outweighed by the harm they prevent.

BUT that doesn't mean a 5-10+ palmar angle is or should be the norm for all horses - and, if it is the case that a horse has such a weak heel that it needs extra heel height to avoid over-stressing the coffin joint and tissues at the back of the foot, aren't we ethically obligated to ask whether we should be exposing such a horse to high impact work - with or without that elevation of the palmar processes?

If Dr Strasser's calculations on load on the coffin joint are correct - the steeper the front feet are, the greater the load on the front of P3 and the greater the potential for laminar strain, solar horn damage and damage to the distal edge of P3. And that's aside from the question of how much persistently elevated palmar/plantar processes affect circulation.