Biomechanics, Inbreeding & Breakdowns

[Shammy Davis]

Here are some problem areas related to the hoof:

Small Hooves
Large/Flat Hooves
Mule Feet
Coon-Footed
Club Footed
Contracted Heels
Thin Walls
Flared Hoof Walls

This thread has come to stand still. I think one of the problems we face is finding or identifying TB racehorses who suffered w/inherited flaws and were then placed into breeding.

With the exception of Big Brown, I have drawn a blank. The sample is just too large and, of course, the environmental factors will cloud the reasons for the flaw.

There has to be an approach. Someone on the Racing Board suggested that the sampling come from a juvenile crop. But how would you it follow it. That would be a very time consuming undertaking.

[Shammy Davis]

Just another thought, hooves might be difficult to connect to unsoundness simply because of the complicated nature of the way they are cared for, the way they wear, the intricate connective structure up through the knee and shoulder, and the effect of nutrition and environment.

I was rereading a section in THE PRINCIPLES OF HERERITY APPLIED TO THE RACEHORSE and Dr. Robertson went into an extensive discussion of roarers and bleeders. He proposes that these are definitely inheritable traits and gives examples.

We would have a better chance locating and designating a horse as roarer than we would definitely designating thin walled shelly hooves as inheritable for a particular horse.

We may also find the same relationship w/bleeders.

[diomed]

Speaking of bleeders, wasn't Herod known to be one and pass on this trait? I seem to recall reading this in numerous old publications.
(I am going to have to look up the resource from many of my "old" books. LOL!
Very interesting thread here. Fascinating.

Not trying to stray the current topic but am I the only one perplexed by the lack of knowledge in the TB gene pool of negative mutations. There has got to be some that could have been isolated in the past and it boggles my mind that a genetic cousin(QH) with a much more incomplete stud book has better modern genetics than than the TB.
But then again, TBs wont even allow AI or ET's so it does kind of make sense.(giggles)

[vineyridge]

Pocahontas from the early 1800s was a roarer and came from a dam who was supposed to also be a roarer. If she passed it on to her foals, it certainly hasn't lasted in either German WBs or TBs. She was the dam of so many great horses (mares and studs) in the shed that the modern TB wouldn't be what it is without her.

Oops, didn't read the "Roarers" post before posting this.

[Shammy Davis]

http://www.ivis.org/proceedings/aaep/2000/39.pdf

[Shammy Davis]

http://www.spiletta.com/UTHOF/sirbarton.html

Sir Barton had such soft, shelly hooves that he often lost shoes during races, even throwing all four shoes in one event. Piano felt was inserted between his shoe and hoof in an attempt to reduce the pain caused by hard, fast racetracks. The constant discomfort may have been part of the cause of Sir Barton's unpleasant disposition. The colt was a grouchy snob, disliking people, horses, and other animals with the only possible exception being his groom, Toots Thompson.

[Shammy Davis]

http://www.grayson-jockeyclub.org/newsi ... ryfoot.pdf

[Shammy Davis]

http://www.grayson-jockeyclub.org/newsi ... y_feet.pdf

[vineyridge]

On another conformation note:
I've recently been looking at a whole lot of photos of long dead TBs, and one that is striking is how long the gaskins used to be in many of the Europeans. I'm thinking Blenheim and Mumtaz Mahal, as well as the Tetrarch. Haven't done enough looking to see if long gaskins were also common in North America or if shortening the gaskin is a modern trend or was always common in some lines of TBs. Usually, at least in sprinters, the long gaskin was also matched with long cannon bones.

Any thoughts on this?

[Shammy Davis]

Vineyridge: Long gaskins are the ideal for many light working breeds. I can't think of many light breeds that don't benefit from this characteristic. Trotters TW, saddle breds, and light carriage horses come to mind. This is JMO, as it is not something that I have paid particular attention to it. Why do you think that the TB is being bred away from the long gaskin?

[xfactor fan]

Secretariat and short cannon bones.

If anyone is interested in the inherentance of this trait. Links are all to the Sporthorse Database, they often have multiple images of the same horse and you can zoom in on the image.

We know Secretariat had long forearms and short cannons.

http://www.sporthorse-data.com/d?d=secretariat&x=0&y=0

Bold Ruler Long forearms, medium cannons
http://www.sporthorse-data.com/d?showpi ... 1207605970

Miss Disco Long forearms, short cannons
http://www.sporthorse-data.com/d?i=396969

Discovery long forearms, medium/short cannons
http://www.sporthorse-data.com/d?i=56064


Fair Play Long forearms short cannons
http://www.sporthorse-data.com/d?i=165066

Somethingroyal Medium, medium cannons
http://www.sporthorse-data.com/d?i=594193

Princequillo long forearm, short cannon
http://www.sporthorse-data.com/d?i=30391


Secretariat offspring

Academy Award Long forearm, short cannon
http://www.sporthorse-data.com/d?i=10005069

Careless Secretary long forearm, medium cannon
http://www.sporthorse-data.com/d?i=10545162

Risen Star long forearm, medium/short cannon Dark photo, hard to see.
http://www.sporthorse-data.com/d?i=10006507

Just from a quick look, short cannons do seem to run in certain families. It does NOT seem to be a dominant, nor does it follow male or female lines. I'd put it in the recessive autosomal chromosome family. Most likely with lots of co-factors.

Now the question is do short cannons contribute to speed, and are they worth selecting for???

[Dave C]

I think you may be barking up the wrong tree in thinking about how the growth of these bones are controlled.

I read a study (don't remember the journal, Developmental Genetics?) a few years back about a couple species of fish in deep lake in Africa. They looked nothing alike, lived in different strata of the lake so their was very little or no intermingling so the researchers assumed they were completely different species. When the sequenced the DNA however they found that the two 'species' were virtually genetically identical. The difference between the two 'species' were in genes that controlled various hormones during development. The genes were not off or on but rather less active or more active. The researchers then proceeded to artificially amipulate those hormone levels for developing eggs and fry, and by doing so were able to make one 'species' look like the other and vice versa.

In the horse we know that the growth plates in different bones of the leg close at different times indicating that those osteocytes are reacting to different developmental hormone levels in different ways. In effect what I'm saying is that the gene pattern that causes the legs to develop in a certain ratio is also going to be affecting everything else that those hormones affect.

[Patuxet]

Here are some actual forearm / front cannon measurements:

Mr. Prospector 26 / 13.25
Seattle Slew 25.75 / 12.75
Secretariat 27.5 / 13.5
Fappiano 26 / 13.5
Halo 26.26 / 12.75
In Reality 25.25 / 12.5
Raise A Native 27.5 / 13.5
Roberto 26.75 / 13.25

From Frank Mitchell's "Racehorse Breeding Theories", Chapter 6 "Biomechanics and Mating"

[Nessa]

Vineyridge: Long gaskins are the ideal for many light working breeds. I can't think of many light breeds that don't benefit from this characteristic. Trotters TW, saddle breds, and light carriage horses come to mind. This is JMO, as it is not something that I have paid particular attention to it. Why do you think that the TB is being bred away from the long gaskin?

Juding by the breeds you've highlighted perhaps long gaskins are a sign of stamina. All of those breeds are known for being able keep a strong pace for long distances.
I'm thinking more speed when you say shorter gaskins. Quick engagement, lots of power, and quick turn over rate in the stride.
The shorter canons may lower the center of gravity, like in a wrestler making the horses quicker and more handy. All that may make the horse speedier.

[vineyridge]

The Nasrullah family were mostly sprinters of the old type--the greyhound type. If you look at the Sport Horse Breed database of Mumtaz Begum, her sire, her dam, Nasrullah, Nearco, The Tetrarch, and Bold Ruler, they all had what I would consider long gaskins. Mumtaz Begum looks down right deformed, her gaskins and hind cannons are so long.