Horses are superb athletes but not immune to muscle problems. Muscle issues affect the whole body and can escape detection as a performance problem. Signs to look for include:
- no/low enthusiasm for work
- sweating in excess of exercise level or environmental temperature
- muscle groups poorly defined; failure to muscle up appropriately in response to training
- muscular twitching or pain on palpation
- texture of muscle is unusually firm (triceps and quadriceps)
- seems lame or sore “all over”
Laboratory studies will show muscle enzymes CK and AST at upper normal or above normal levels. This is commonly seen during conditioning but should return to normal as the horse becomes fit. The check list of support nutrients for muscle includes:
Crude Protein: Research is emerging to suggest that the protein requirements of very active horses may be as high as 2 g/kg BW or 1000 grams/day for a 500 kg horse. If your diet is high quality forage or mixed forage/grain there’s a good chance the horse is getting that much anyway. If not, consider making up the difference with high quality protein sources such as whey, soybean, egg, pea or linseed. With soybean and linseed you want defatted meal. For whey, pea or egg protein, get a protein isolate.
Salt: Optimal hydration is impossible without adequate salt (1 to 3 oz/day minimum). Water is essential for biochemical processes in the muscle cell, storage of glycogen, delivery of nutrients to the cells and efficient cooling.
Vitamin E and Selenium: These two nutrients play central roles in arming the muscle cells with effective antioxidant defenses. Energy production is the major source of free radicals in the body and levels jump with exercise. Requirements may be many multiples of the minimum recommendation of 1000 IU vitamin E and 1 mg selenium for a 500 kg horse. If your horse is having muscular issues, test serum vitamin E and whole blood selenium levels to see if these may be involved.
Magnesium: Suboptimal magnesium intake may manifest as fine muscular twitching, muscle cramping/irritability, even gait disturbances. Dosage is ideally determined after hay and diet analysis but 5 to 10 grams may be tried short term to see if the signs improve.
L-carnitine: L-carnitine is a carrier molecule needed to get fats inside the mitochondria so they can be burned. It’s acetylated form, acetyl-L-carnitine, plays a key role in regulation of energy generation. Research has shown that supplementing with L-carnitine enhances the muscle response to training and increases aerobic energy generation which is documented by lower levels of lactate.
L-Leucine: Skeletal muscle has very high levels of branched chain amino acids, particularly leucine. Leucine has four important functions. It is a structural amino acid, meaning it is used to build bulk. Leucine can also be burned directly as an energy source, reducing the demand on stored glycogen and blood glucose. A metabolite of leucine, beta-hydroxy-betamethylbutyrate or HMB, is a potent regulator of muscle hypertrophy. Finally, when leucine is broken down for energy it can help restore glucose levels. The amino group of leucine gets transferred to pyruvate to form alanine. Alanine travels to the liver and is converted to glucose. Leucine is most effective given in a small amount of corn syrup as a carrier, immediately before and/or immediately after exercise. Dosage is 10 grams.
L-glutamine: L-glutamine is an amino acid that can support and drive the synthesis of glutathione. Glutathione is the most important antioxidant molecule in muscle cells. [Note: Selenium also needed for glutathione function.] Muscles that are sore or tight may benefit from L-glutamine, 15 grams/day.
It may take some experimentation to find the right support modalities but muscle issues plaguing performance horses can often be resolved nutritionally.
Eleanor Kellon, VMD