From sales yearlings to seniors, pleasure trail horses to upper echelon competitors, caretakers and owners are attuned to muscle bulk. In addition, muscle dysfunction or pain is a grossly underappreciated cause of suboptimal performance whether it be a young horse that has training interrupted for being “colt sore” or a horse hitting a wall in active training or during performance.
Strength and endurance do not require excessive muscle bulk.
While we are always on the alert for lameness and joint, tendon or ligament issues, even experienced riders and trainers may miss signs of a muscle problem. Bulk should be both breed and sex appropriate. Don’t mistake a layer of fat for muscular development (e.g. the back and rump both have a significant layer of fat). Familiarize yourself with what the body and muscle definition looks like on horse of a fit body weight – body condition score 5.
A lean Warmblood is muscled much like a Thoroughbred, with the back flat and little to no crease down the midline. When there is a prominent back crease, the difference is fat.
As a horse becomes fit, there is some increase in muscle size from cellular hypertrophy and increased levels of glycogen and water. Coupled with less subcutaneous fat, the end result is muscles that show better definition but not a huge increase in bulk. American Pharoah had the most well defined musculature I have ever seen. Study some photos of him compared to other racehorses.
Look at the shoulder and forearm muscle definition of American Pharoah (Bloodhorse photo)
If you don’t see muscles changing like this during training there is something wrong.
It’s also important to know what healthy muscle feels like. It should not feel hard like someone flexing their biceps. Healthy muscle at rest has the consistency of an uncooked beef roast. It’s not mushy or flabby but not rock hard either. The triceps above the elbow and quadriceps above the stifle are good areas to check for resting muscle tone. You cannot check over the rump because a layer of fat and extra thick skin are covering the muscle.
Healthy muscle also stays relaxed when you are palpating it. There should be no resistance or suggestion of pain from the horse. There should never be obvious spasm or trembling (fasciculation).
The next blog on this topic will cover nutrients that can help with muscle problems. One point I want to leave you with though is that muscle cannot be bulked up by feeding a protein supplement. Only growth or exercise can force muscle to bulk up (legally anyway!). The only exception to this would be a horse that is not getting enough protein overall in the diet or enough of the amino acid lysine. Total protein deficiency is rare but lysine deficiency may not be, especially in horses getting only moderate quality hay and little supplemented grain. In that case it is much easier and more cost effective to supplement with lysine alone, or a lysine-methionine-threonine combination product. Give 10 grams of lysine per day for the average size horse.
Eleanor Kellon, VMD