Topline Part One: 4 components critical to understanding a horse’s topline
1. The science behind building muscle
Muscle growth is controlled by two opposing forces. One is a complex protein (mTOR) that controls the building of muscle and is activated when a muscle is used. The other (MPS) is responsible for muscle protein breakdown and becomes more active when the body is in need of additional fuel sources.
As a muscle is put under tension, damaged with use, or under metabolic stress our builder (mTOR) does work building and strengthening the muscle fiber using available protein. We say “protein” like it’s a simple product. But really it’s not. There are 10 essential amino acids (cannot be produced by the body) that are vital for the body to synthesis protein, absorb nutrients, and repair damaged tissue. Leucine, isoleucine, and valine are the amino acids believed to be responsible for 60% of muscle tissue.
2. Muscles of the topline
Everyone talks about a horse’s topline. But what does that really mean? I’ve tried to illustrate the muscles included in the topline below. You’ll have to forgive any malformation of the muscles I’ve drawn and this will be best viewed on a larger screen. The muscles depicted are the Splenius (purple), Trapezius (Yellow), Rhomboideus Thoracis (orange), Longissimus Dorsi (Green), and Gluteus Medialis (Blue).
The topline is responsible for lifting the horse’s back and shoulders, extending the neck, and engaging the hind legs. This is the powerhouse of the horse in movement.
3. Reasons for a poor topline
The obvious reasons for a horse to have a poor topline is a lack of exercise and/or a poor diet. Remember, muscle is built when mTOR is activated. But, mTOR can’t build muscle if it doesn’t have the material (protein – amino acids) to build with.
But there are other reasons a well-kept horse may lose topline. A hidden enemy of a good topline is a poorly fitting saddle. A saddle that limits the muscles of the back or shoulders or a saddle that causes pain to the horse will cause your horse to compensate by avoiding the use of the muscles impacted by the saddle.
Another reason for a poor topline in an otherwise fit horse may be the type of exercise the horse receives. Horses with poor posture and movement need to be re-trained to carry their body correctly. This can be hard for the horse and requires focus and slow adjustments over time.
4. Topline scoring
Mid-Rivers Equine Center has an article with a great explanation of the Topline Evaluation Scoring (TES) Chart. An ideal topline includes a well-rounded back, loin, and croup. This is a horse with enough strength to perform the work required of it. In contrast, a horse with a slightly lower topline score will lack muscle in the back area. Saddles may be hard to fit and soreness may cause performance and attitude issues. When the lack of muscle extends from the back into the loin area it is important to understand that the horse will only be able to ‘work’ for short periods of time. Overworking a horse with a lack of muscle in the back and loin is a risk and training periods should be kept short. In the most severe cases, the horse will lack muscle along the back, loin, and croup. The croup will appear pointed and the muscle between the vertebrae and hip bones will be sunken in. This horse is in a severely weakened state and care should be taken to improve overall conditioning before any type of strenuous work is asked of the horse.
I highly recommend reviewing the chart and evaluating your own horse. Here is a great video by Nutrena explaining how to do your own topline scoring.
Next Up
In part two of our topline discussion, I will look at the topline and how genetics, nutrition, and exercise impact its quality or condition.
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