Building Top Line in Horses: Protein, Amino Acids, Antioxidants and Expert Tips

Why Protein Matters

A well-developed topline—strong muscles across the neck, withers, back, and croup—is the hallmark of a sound, powerful horse. Yet many owners struggle to build these muscles, even with regular exercise. In reality, achieving a solid topline requires more than just workload; it relies on the right nutrition, including quality protein, essential amino acids, antioxidant support and smart management strategies. Let’s explore how these elements come together to shape a horse’s strength, performance, and longevity.

💪 1. The Role of Protein in Topline Development and helping horses “Muscle Up”

Protein is essential for muscle repair and growth. However, not all proteins are equally effective.

Protein plays a vital role in muscle development for horses, acting as the building block for tissue repair, growth, and overall topline strength. But it is also essential for things like hormonal balance, immune support and energy provision. If a horse isn’t getting enough protein you are going to run into trouble. How much protein they need is determined by their weight and by their workload. When a horse undergoes training or increased workload, muscle fibres experience microscopic damage that must be repaired through muscle protein synthesis—a process dependent on a sufficient and balanced supply of dietary amino acids. While total protein intake matters, the quality of that protein—meaning its amino acid composition—is even more critical. Essential amino acids, particularly lysine, threonine, and leucine, are key to effective muscle growth and optimal topline development depends on all 10 essential amino acids. Lysine is often the first-limiting amino acid in equine diets and is crucial for collagen formation and lean tissue development. Leucine, a branched-chain amino acid (BCAA), acts as a trigger for muscle protein synthesis, essentially turning on the body’s muscle-building machinery after exercise. Without adequate amounts of these amino acids, even high-protein diets can fall short in supporting topline gains. High-quality forages, well-balanced feeds, and targeted supplements help ensure horses receive the necessary nutrients to build and maintain strong, functional muscle. Ultimately, optimal protein intake doesn’t just influence appearance—it supports performance, recovery, and resilience in every working horse.

🔬 2. What Amino Acid Builds Muscle and what is the difference between Lysine and Leucine? 

Animal nutrition experts highlight leucine as the “switch” that initiates rebuilding, while lysine helps maintain muscle structure.

Lysine

As the first-limiting amino acid in most equine diets, lysine must be provided in adequate amounts for protein synthesis to occur effectively—without it, muscle growth and recovery are significantly compromised, regardless of overall protein intake. Lysine is essential for building collagen, a key structural component of muscle and connective tissue, and supports the maintenance of lean muscle mass during training, growth, or rehabilitation. Supplementation with lysine has been shown to support topline muscle development in both young and older horses (Graham‑Thiers & Kronfeld, 2005), especially in horses on forage-based diets or those in hard work with higher protein demands. By ensuring horses receive enough lysine—either through high-quality protein sources like soybean meal or targeted amino acid supplements—owners can more effectively support muscle tone, strength, and post-exercise recovery, making lysine a cornerstone of any performance horse’s nutritional program.

 

Leucine

Leucine is a branched-chain amino acid (BCAA) and a key nutritional trigger for muscle protein synthesis in horses, playing a crucial role in both muscle development and post-exercise recovery. Unlike other amino acids that serve mainly as building blocks, leucine acts as a metabolic signal that activates the mTOR (mechanistic target of rapamycin) pathway—a key driver of muscle growth. This means leucine doesn’t just contribute structurally to muscle tissue; it actually tells the body when to start building and repairing muscle fibres after exercise. Horses undergoing training or muscle rehabilitation greatly benefit from adequate leucine intake, particularly when combined with other essential amino acids like lysine and threonine. Research in other species, and emerging studies in equine nutrition, suggest that leucine enhances the efficiency of protein utilisation, helping horses recover faster and build lean tissue more effectively (Deboer et al., 2018). For horses in hard work, leucine may also help limit muscle breakdown during exercise, preserving muscle mass and promoting faster adaptation to training. Because forage-based diets can be low in leucine, targeted supplementation—especially post-exercise—can help optimise muscle response and topline development, making it an increasingly important focus in modern equine nutrition strategies.

🛡️ 3. Antioxidants & Recovery

During training and recovery, horses experience increased oxidative stress caused by the production of free radicals. Antioxidants play a vital role in neutralising these free radicals and supporting efficient post-exercise recovery. One of the most important antioxidants for equine athletes is vitamin E, which stabilises cell membranes and supports immune and neuromuscular function. Horses in regular work, especially those with limited pasture access, often require additional vitamin E to meet increased physiological demands as the amount of vitamin E falls dramatically once grass is cut for hay/haylage and degrades rapidly when stored. Grapeseed extract is another potent antioxidant, rich in polyphenols and oligomeric proanthocyanidins (OPCs), which have been shown to aid circulation and support vascular integrity. Additionally, rosemary extract provides powerful plant-based antioxidant compounds such as carnosic acid and rosmarinic acid, which not only combat oxidative stress but may also support the horse’s inflammatory response. Together, these ingredients create a synergistic effect, aiding recovery times, soothing tired, aching muscles, and maintaining overall muscle health. Including targeted antioxidant support in a performance horse’s diet—especially when paired with quality protein and amino acids—can make a meaningful difference to recovery, resilience, and topline development over time. Read more about this topic in our blog on free radicals and the role of antioxidants.
 

🔄 4. How Much Protein does a Horse Need?

Many owners think that protein is heating for horses and that high protein feeds should be avoided. Protein is actually essential for growth, repair and overall health as it is involved in many bodily functions. The amount of protein a 500 kg horse needs depends on their age, workload, and physiological status (e.g., maintenance, growth, lactation, or training). Quality matters: It is important to realise that a diet may meet daily protein quantity targets but still lack key amino acids like lysine or leucine needed for muscle development and building top line.

Workload/ Status	Protein (g/day)	As a % of Total Diet
Maintenance/ Rest	630-700g	8-10%
Light	700-850g	9-10.5%
Moderate	900-1000g	10-11%
Heavy (eg. Eventing)	1100-1200g	11-12%
Growing Youngstock	1000-1500g	12-16%
Lactacting Mares	1800-2000g	14-16%

 

A 500kg performance horse in moderate work needs roughly 900-1000g of crude protein per day which equates to 10-11% of their total daily dry matter intake. This protein will come from a variety of sources including forage, concentrates and any supplements.

Analysis of UK grass/hay suggests that the average protein level is 6.5%. That means that if your 500kg horse is consuming 10kg (2% body weight) of grass/hay per day and is in moderate work then they are running at a protein deficit of 350g (35%) per day. Can you see how that could very quickly become a problem without supplementation?

In order to support muscle growth, amino acid ratios matter most. Quality supplements should aim to supply as a minimum:

• Lysine: first-limiting essential amino acid important in collagen formation
• Leucine (BCAA): stimulates protein synthesis
• Threonine & methionine: (naturally present in whey protein) to support muscle maintenance
• Vitamin E + selenium: for antioxidant protection

Whilst the actual muscle development and topline building process is important, it is equally important to support your horse’s recovery from the stresses and strains of training that can lead to oxidative stress.  Useful ingredients to look for include rosemary extract (a natural antioxidant with adaptogenic properties), Taurine (an amino acid that supports muscle function and relaxation through its role in maintaining calcium levels in the body), Tyrosine (used to support normal cognitive function, particularly important during stressful situations such as during hard training/competition), Arginine (important for the nitric oxide pathway which supports blood flow and the provision of oxygen and nutrients to muscles during exercise) and Glutamic Acid (important for muscle metabolism, aiding recovery and maintaining immune function). This list is not exhaustive and there are many natural ingredients that further support these processes such as Ginger, Beetroot, Ashwagandha, Spirulina and Milk Thistle.

The best horse supplements for muscle gain will include ingredients that support not just muscle building but muscle recovery. Equell Muscle Up contains all of the above ingredients and more!

📝 5. Top Tips On How to Build Topline in Horses

Here are nine practical strategies to support optimal topline development:

1. Assess for underlying issues

Conditions like PPID (Cushing’s) or PSSM can inhibit muscle gain. Always consult your vet first before increasing your horse’s training or feeding regime

2. Prioritise protein quality, not just quantity

Feed high-quality forage supplemented with protein feeds rich in lysine and leucine. Ensure balanced amino acid intake of the essential key amino acids.

3. Use targeted amino acid supplements

Products rich in lysine, leucine, threonine, and BCAAs support muscle function and growth efficiently. Ensure your base diet is adequate for workload before adding additional supplements and consult your equine nutritionist if you are unsure.

4. Support with antioxidants

Ensure vitamin E and selenium are included daily at suitable levels —either via feed or supplements. Be careful when supplementing with selenium - consider all sources within your horse’s diet to avoid excessive amounts being fed, which may be harmful. If you have specific queries relating to our products our nutritionist team will be happy to help, just drop us a line at info@equell.co.uk

5. Combine nutrition with exercise

Topline muscles respond best to low-impact, topline-focused work: hill work, pole work, backing up, and transitions all play their part in building strong topline in horses. All exercise should be carefully planned and increases in workload introduced slowly to allow the horse to adapt to training.

6. Stretch and posture work

Daily stretches encourage proper alignment and engagement of the topline muscles. The use of bodywork, massage, chiropractic treatments etc can all be beneficial as part of a holistic work plan.

7. Optimise saddle fit

A poorly fitting saddle can significantly inhibit topline development by restricting range of movement and causing discomfort —check fit regularly, especially as muscular tone changes and your horse gets stronger.

8. Provide adequate turnout

Time at liberty promotes natural movement and muscle usage. Creating a track system for your horse has been shown to hugely influence daily movement vs conventional paddock grazing. Remember to balance turnout time with grass intake where there is a lot of grass cover or grass growth occurring in your paddock.

9. Monitor progress

Use body scoring and feel to gauge topline development—firm muscle vs. spongy fat. Weighing your horse is useful but is not always an accurate indicator on its own as your horse may gain weight but be in better physical shape through increased muscle development vs fat deposits and cresty necks.

🎯 6. Key Takeaways

Key Element	Role in Topline
Lysine	Important for collagen formation
Leucine (BCAA)	Activates muscle protein synthesis
Antioxidants (Vit E, Se)	Neutralise free radicals
Targeted exercise	Encourages muscle engagement and recovery
Saddle fit & turnout	Prevents muscle strain, encourages muscle usage

Achieving the perfect topline takes science + strategy + consistency. Focused nutrition, intelligent training, and recovery support techniques work synergistically to build and sustain strength along the back. A strong topline is essential for long term health and wellbeing of the horse and for optimal athletic performance, whether they are competing in dressage, showjumping or eventing.

📌 References

Graham‑Thiers, P. M., & Kronfeld, D. S. (2005). Amino acid supplementation improves muscle mass in aged and young horses. Journal of Animal Science, 83(12), 2783–2788

DeBoer, L. M., Galyean, M. L., Heinze-Milne, S. D., & Lawrence, L. M. (2018). Leucine activates mTOR signalling and stimulates protein synthesis in cultured equine satellite cells. Journal of Animal Science, 96(Suppl_2), 348–349