Page 71 - March 2017

Skeletal muscle is made up of bundles of individual muscle fibers, or myocytes, that contain many myofibrils, which are strands of proteins that grab
on to each other and pull to cause muscle contraction. Skeletal muscle is
a genetically determined mixture of both slow and fast twitch fiber types.
humans) have two basic types of muscle fibers— slow twitch (type I) or fast twitch (type II). Slow twitch muscle fibers facilitate endurance feats, such as distance running. Fast-twitch muscle fibers fatigue faster, but are used in powerful bursts of movement like sprinting. “There are also some fibers that, with careful training, can go either way,” Casner explains.
Skeletal muscle is made up of bundles of individual muscle fibers called myocytes. Each myocyte contains many myofibrils, which are strands of proteins (actin and myosin) that can grab on to each other and pull. This is what shortens the muscle and causes muscle contrac- tion. Most horses and humans have a combination of slow twitch (Type I) muscle fibers and fast twitch (Type II) muscle fibers. Fast twitch fibers can be further categorized into Type IIa and Type IIb fibers.
These differences influence whether a horse is a natural sprinter or a distance horse, and also influence how the muscles respond to training and physical activity since each fiber type is unique in its ability to contract in a certain way. The muscles contain a genetically determined mixture of both slow and fast fiber types. The slow Twitch (Type I) are more effi- cient at using oxygen to generate more fuel for continuous, extended muscle contractions over a long period of time because they fire more slowly than fast twitch fibers and can go for a longer time before they fatigue.
Every good athlete is a combination of natural ability and training (nature and nurture). “The type of muscle fibers a horse inherits is the genetic (nature) part of what that horse can do and how we train him is the nur- ture part—assisting or modifying his ability,” explains Casner. We can help a horse with good training, but it is difficult to make a natural sprinter into a distance horse or vice versa.
HARD TO TELL BY LOOKING AT HIM
“What we see on the outside is not indica- tive of what that horse’s true potential is. There are some general differences between Quarter Horses and Thoroughbreds, but you still can’t tell by looking at a horse what his natural talent will be for running. Everyone wants to pick a pretty horse at the sale and has an idea in their mind of what that perfect horse will look like. They have an imaginary picture of the type of horse they like and generally select that kind of horse. This picture is based on their own experience over
the years regarding what has worked for them,” Casner says.
“But when horses go through the yearling sales, it becomes a beauty contest. There are always some not-so-pretty horses that are overlooked by astute horsemen and expert horse selectors, yet end up being very good racehorses. It’s a gamble
at a sale picking out horses you think will run, but that’s where the market is and this is a person’s resource for young horses unless they breed the horses themselves. A person just has to combine a knowledge of pedigree, evaluation of conforma- tion, etc., and scope the horses and look at their throats,” says Casner.
“At the sales, we vet them to the extreme sometimes, and it could help tell us whether
a horse might be able to hold up to training. Correct conformation is important. In the front end, correct angles help determine whether the horse can hold up. We’ve all seen some horse with poor front end conformation that sure could run, but they also have to be able to stay sound,” he says. A horse is less apt to break down if the front legs are correct.
“The law of physics comes into play. Poor angles put more stress on joints and certain parts of the feet and legs. If they can’t hold up, it doesn’t matter how fast they can run. I’ve had a lot of fast horses that had less than ideal conformation. Well
Armed was extremely fast, but pigeon-toed. We were able to keep him sound by running him on synthetic surfaces, which are more forgiv- ing,” says Casner.
“You see some horses in a Quarter Horse race that are able to get out in front and sustain that effort for a full quarter of a mile. Those have the potential to win futurities, but it’s not always easy to select those athletes. For much of my career I’ve been more involved with Thoroughbreds than with running Quarter Horses, but in my early days I was involved with Quarter Horse racing. Breeders have infused a lot of good, fast
Every good athlete is a combination of natural ability and training. The inherited type of muscle fibers, heart, conformation and talent makes the biggest difference in determining what a horse might be able to do and can help determine if the horse may be a good distance runner or a better sprinter.
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EQUINE HEALTH