Developing muscles need protein
Clearly, muscle development cannot occur without corresponding stimulation through training. So diet alone will not increase muscle, and the amount of physical activity needed to achieve visible muscle growth is often underestimated. However, diet can limit muscle growth despite adequate training if it lacks the proper amounts of nutrients to build up the protein structures.
Physical activity and diet therefore go hand in hand when it comes to muscle building. It may be compared to building a house, with trades workers representing physical work and the building materials representing diet. No matter how many trades workers you recruit, if there is not a continuous supply of building materials, they can only finish the house at the speed allowed by the arrival of raw materials. On the other hand, pallets brimming with building materials are of no help if the workforce to install them is lacking.
Full steam ahead: these nutrients build muscle
Amino acids are the building blocks of muscle protein, which is why it is important that horses in training be given sufficient amino acids. Some amino acids can be produced by the body itself, whilst others must be supplied through diet – these are called essential amino acids. In mammals, these are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
To build its own muscle protein from amino acids, the body needs the appropriate training stimulus as well as sufficient amounts of all essential amino acids. A supply shortage of just one amino acid can bring the body's own protein synthesis to a standstill, because the cell nuclei for each protein provide very clear instructions in their genetic material as to which amino acid is to be incorporated where. This precisely determined primary structure of the proteins allows the long amino acid chains to be formed so that the protein can fulfil its later task.
Let’s look at it again through the lens of our house construction: If masonry stones are missing, the masons cannot compensate with roof tiles. And until the masonry work is finished, the roofers can’t begin with their own work.
Most amino acids are already present in sufficient amounts in the horse's base feed. But there are three amino acids that, due to their scarcity, may limit the progression of muscle development. These are methionine, lysine, and threonine. The horse’s diet should therefore be supplemented by these three amino acids during training periods.
Quality before quantity: specific amino acid supplementation
All proteins are made up of amino acids – so the idea has been to simply supplement high-protein feeds to build up muscle. This only works to a certain degree – not all protein is equally available to the horse, and an excess supply above the requirement puts strain on the entire organism. The protein in feed supplements, then, should be of high quality and easily digestible in the small intestine. Good sources include linseeds, sunflower seeds, and brewer's yeast. Cereals and lucerne, although frequently recommended by horse owners, are less suitable due to their amino acid patterns and protein digestibility. (The differences between protein sources in horse feeds are discussed in more detail in our article Protein in horse feeds
Muscle development should be supported through the targeted supply of the amino acids methionine, lysine, and threonine through complementary feeds – this puts no unnecessary strain on the large intestine, liver, and kidneys. This ensures that the horse gets the necessary amino acids without inflating the total protein in the feed. Another advantage of adding amino acids is that their pre-caecal digestibility is then almost 100 percent – these amino acids are therefore fully absorbable in the horse instead of entering the large intestine partially undigested.
To optimise the effects of amino acid supplements, you can feed the amino acid supplement around the time of the work. A time span of about two hours before work until shortly afterwards ensures a precise supply for the muscles.
Other important nutrients for muscle development
When you are building muscle, the body unavoidably comes under stress due to the challenges imposed. Only then does the organism recognise the need to build up muscle. During and after intensive training sessions, the metabolism is running at full speed. As long as the organism is working under stress, the muscles need more oxygen, energy sources, and antioxidants. The heart and respiratory rate increase to supply more oxygen. The muscle pigment myoglobin also contains oxygen reserves.
Longer-working muscles get energy mainly from glucose and fatty acids. Muscle stores glucose in the form of glycogen, which it breaks down during strenuous activity. It can also absorb glucose as an energy source from the blood. In order for the muscle fibre to be able to convert glucose into energy in the mitochondria, it needs vitamin B1 as a co-enzyme. Vitamin B2 is also an important co-enzyme for energy metabolism.
Muscle likewise uses fatty acids from its own (and external) reserves. In order for fatty acids to enter the mitochondria, they must be bound to the amino acid L-carnitine. This is the only way it can cross the mitochondrial membrane. In times of more extreme stress, the supplemental feeding of L-carnitine can help to prevent shortages in endogenous synthesis and associated loss of performance.
If a high amount of energy is burned during work, the body must naturally replenish the consumed energy through feed relatively soon; otherwise, the horse’s body cannot build muscle mass and instead will lose substance. The point after which forage alone is no longer enough to cover the energy requirement, and which energy sources are best for which horses, are topics discussed in our article Sources of energy in horse feeds
Whenever the body uses a large amount of oxygen, it produces what are known as oxygen radicals or reactive oxygen species. These are formed by random chemical reactions and can damage cell membranes. That is why all cells contain enzymes and antioxidants that convert these oxygen radicals into harmless oxygen compounds. Selenium is part of glutathione peroxidase and therefore an important nutrient for horses in hard work. The same applies to vitamin E as an antioxidant. Vitamin C is also an important antioxidant as well as involved in the endogenous synthesis of L-carnitine.