A common question that nutritionists often hear from horse owners is “What should I feed to help my horse build muscle?” Unfortunately, the answer isn’t as simple as just adding a supplement or switching feeds. Muscle development depends primarily on an appropriate exercise programme, since muscle can only grow in response to being used – a retired horse who spends most of its time in the stable is unlikely to see much muscle gain. This principle is the same in humans; muscles need to be used, and no amount of protein shakes or supplements will help if you’re mostly sedentary.
That being said, alongside a suitable exercise regime, nutrition can play a key supporting role in improving muscle tone. To develop top line, horses need an adequate supply of amino acids, which are the building blocks of protein. They also need to be consuming enough dietary energy (calories) to maintain a healthy body weight. Horses can obtain protein from multiple sources, including grass, forage and their bucket feed. However, it’s not just the quantity of protein that matters; the protein quality is just as important.
What is protein?
Protein is an essential component found in all tissues in the body, making up about 20% of its composition, second only to water. It’s not just muscle either; enzymes, hormones and antibodies are also proteins, highlighting their essential role in maintaining health.
Proteins are made up of chains of amino acids linked by peptide bonds. The type and function of the protein are dependent on both the length of the chain and the specific amino acids included. While the horse’s body can produce some amino acids on its own, there are nine which must be obtained through the diet. These are termed “essential” or “indispensable” amino acids because the body can’t produce enough to meet its needs.
The quality of a dietary protein source is typically judged by the levels of the essential amino acids it contains. This means that protein sources which contain a higher proportion of essential amino acids are generally considered to be of better quality.
What is lysine, and why do horses need it?
Lysine is one of the essential amino acids, meaning it must be supplied in the diet. It’s also the only amino acid for which a specific daily requirement has been determined in horses. In addition, lysine is what’s known as the first limiting amino acid. This means that while there can generally be an abundant amount of protein in the diet, the horse can still be protein-deficient if they aren’t having enough lysine. Think of it like building a house – you can have plenty of bricks, but if you don’t have enough mortar, then you can’t complete the job. Lysine is particularly important for youngstock because a deficiency will limit growth and development.
Muscle Supplements: Are they worth it?
For horses who are struggling to build top line, there is a growing trend to reach towards specific ‘muscle-building’ supplements, which are often marketed for their high amino acid content. Such products don’t come cheap, though, usually costing around £2 to £3.50 a day for a 500kg horse, which could add up to a bill of more than £1000 for the year!*
Furthermore, when examining the amino acid levels actually being provided, common feed ingredients like alfalfa frequently outperform many commercial supplements. For example, feeding just 2-3 scoops of chopped alfalfa will deliver higher levels of most amino acids than many muscle supplements on the market, including whey or pea protein-based products. Since many horses are already fed a scoop of chopped fibre with each meal, switching to an alfalfa-based option is a simple and effective alternative without the need for additional supplements.
For good doers, it’s worth noting that even just one mug a day of Alfalfa pellets will supply greater levels of many amino acids than the recommended amount of spirulina-based muscle supplements, including around three times the lysine content. This also works out considerably more cost-effectively, at around 16p a day*, so it’s a great way to top up your horse’s amino acid intake without adding too many calories or breaking the bank. Feeding a Stubbs scoop of chopped fibre can provide almost six times the lysine content of such supplements!
Why is alfalfa so high in amino acids?
Alfalfa belongs to the legume family – the same as peas, beans and clover. Alfalfa has a deep root system that enables it to access water and minerals deep in the soil. In many cases, alfalfa roots can reach 4 or 5 metres deep, which is more than double the root depth of typical grass and cereal plants. These deep roots help alfalfa fix nitrogen from the environment and put it back into the soil, as well as incorporate it into plant tissue as amino acids, which can then be transferred to the horse when the alfalfa is eaten.
In addition, the protein content of alfalfa is at its highest when the plant material is still young. Dengie use precision drying techniques to conserve the alfalfa, meaning there is less reliance on the sun to dry the crop, and so harvest can take place earlier before the plant is fully mature. This means the alfalfa produced is more digestible for the horse and higher in natural nutrients.
To put this into context, Dengie’s Alfa-A range of feeds typically supplies around 0.8% of the essential amino acid lysine – approximately twice the level found in average grass hay. Just two Stubbs scoops of Alfa-A Original can deliver around 20% of the lysine requirement for a horse in light work, while just one scoop of Alfalfa Pellets provides an impressive 45%. Feeding alfalfa, therefore, means there is far less reliance on the forage and other feeds or supplements to fulfil the horse’s total daily intake.
Are there any other benefits of feeding alfalfa?
Like other plants, alfalfa makes sugar when photosynthesising, but if it makes more sugar than it needs, it stores any surplus as starch in its roots – the part that horses don’t eat! This makes alfalfa a fantastic choice for horses who can be fizzy or excitable, as it supplies a comparable calorie content to a cool mix or cube but with about 10 times less starch.
Furthermore, studies back in the early 2000s (Nadeau et al., 2000; Lybbert et al., 2007) showed that alfalfa was more beneficial for horses with ulcers compared to grass forages, as the high levels of calcium and magnesium it contains act as natural buffers to acidity. The very low levels of starch in alfalfa are also key to its usefulness for all horses, but especially those with ulcers.
*All prices correct as of June 2025
