Improving muscle condition can yield a whole wealth of benefits for performance and health. Muscle development is impacted directly and indirectly by many factors, some which we can influence, and some that we cannot. These include genetics; exercise; age; health; management and nutrition. Below we discuss how we might adjust diet and management to promote muscle function and development.
To understand how nutrition provides the necessary foundations for muscle development, we need to look at protein.
Protein has many roles in the body, but the largest concentration is as a constituent of muscle, along with hair, skin and connective tissue. Other roles include regulation of metabolic function, immune defences, and cell transport.
When we look at whether a horse is meeting his protein requirement, we not only need to assess total crude protein intake, but also amino acid profile. This is because horses have a requirement for amino acids (building blocks of protein) rather than crude protein. Furthermore, crude protein figures can be misleading; the total amount of protein can appear high, but the quality of this can be low. This is why you will often hear the phrase ‘quality over quantity’ when it comes to protein. When it comes to assessing quality, a key marker is lysine content. For the horse, lysine is what is known as the first limiting amino acid. This means that protein can only be utilised up to the level of lysine in the body, deficiency in this impairing overall protein synthesis.
Protein cannot be stored by the body, so feeding excessively above required levels, particularly if the quality is poor, offers no advantage to the horse, as it must be excreted through a process that uses energy.
It is worth noting that while protein (including lysine) is contained within forage (hay/haylage/grass), the amount that is accessible to the horse is highly dependent on the digestibility of the forage source. A proportion of the protein within forage is ‘locked up’ within the fibre and therefore not available to the horse. The more fibrous (lignified) the forage, the lower the amount of accessible protein. As such, a horse’s protein requirement varies throughout the year depending on available forage - spring grass containing more ‘accessible’ protein than coarse mature hay. This puts increased reliance upon provision of good quality protein (amino acids) in the bucket feed to provide consistent nutrition throughout the year.
Along with forage type and quality, protein requirement also varies with factors such as workload, age, and reproductive status – requirement increasing for growing youngstock, older horses and those in work, reflective of its role in muscle development, repair, connective tissue, and metabolic functions.
Figure 1: Schematic of protein basic constituents
Essential and Non-Essential Amino Acids
Amino acids can be classified as either essential or non-essential, based on dietary importance and availability. In the horse, 21 amino acids have been identified, all but 10 of which are synthesised by the horse through transamination (conversion of one amino acid to another) – these amino acids are termed non-essential. The remaining 10 amino acids (lysine, methionine, threonine, valine, leucine, isoleucine, arginine, tryptophan, histidine, and phenylalanine) are categorised as essential amino acids - the horse cannot synthesise these itself or synthesis is insufficient to meet requirement. Consequently, essential amino acids must be provided in the ration.
Branched Chain Amino Acids
Branched chain amino acids are a further sub-group of essential amino acid that includes leucine, isoleucine, and valine. In humans, BCAA supplementation has been associated with reduced muscle soreness and fatigue during intense exercise.
Leucine specifically, is associated with muscle development and is thought to be a activate the pathway involved in the initiation of muscle protein synthesis (muscle building). The amino acid leucine and its metabolite HMB (ß-Hydroxy ß-Methyl Butyrate) have been suggested to increase muscle mass when combined with appropriate training and nutrition in humans and horses. In horses, leucine (and HMB) has been associated with improved endurance and recovery, reduced muscle damage, reduced blood lactate after exercise, improved maintenance of bodyweight, increased red blood cell count and improved immunity. Further research in horses has also demonstrated an increase in fatigue-resistant muscle fibres in Thoroughbreds supplemented for 45-days with HMB, although no immediate performance improvements were observed. It is evident that tangible advantages are associated with the feeding of BCAA to horses, however further research is required to ascertain the extent of this.
Measuring the Impact of Supplementation
Alongside recording performance parameters, muscle scoring (like body condition scoring but assessing muscle instead of fat) can be used to provide an indication of progress.
Muscle assessment uses palpation and visual indicators to appraise muscle tone and development. There are several scoring systems available; a new scoring system has recently been published providing a descriptive muscle score guide out of 5 (this article is open access, please see references for link). It is important to note that muscle development is not only a reflection of providing the correct building blocks in the diet but also the appropriate training and exercise. A change in muscle condition takes upwards of 6 weeks, subject to workload.
Take Home Points:
Nutrition is just one piece of the puzzle when it comes to muscle development and health. Other key factors such as exercise should also be considered.
Amino acids are the building blocks of protein. Dietary provision of essential amino acids (which includes BCAA) is fundamental and targeted supplementation has been associated with advantageous performance outcomes including muscle building, recovery, and reduced fatigue.
Make use of both body condition and muscle scoring systems to optimise feeding and benchmark your progress.
Busse, N.I., Gonzalez, M.L., Krason, M.L., Johnson, S.E. (2021) β-Hydroxy β-methylbutyrate supplementation to adult Thoroughbred geldings increases type IIA fiber content in the gluteus medius. Journal of Animal Science. 1: 99(10) https://doi.org/10.1093/jas/skab264
Ostaszewski, P., Kowalska, A., Szarska, E., Szpotański, P., Cywińska, A., Bałasińska, B., Sadkowski, T. (2012) Effects of β-Hydroxy-β-methylbutyrate and gamma-oryzanol on blood biochemical markers in exercising thoroughbred race horses. Journal of Equine Veterinary Science, 32: 542–551.
Pallesen, K., Gebara, K., Hopster-Iversen, C. & Berg, L.C. (2023) Development of an equine muscle condition score. Equine Veterinary Education, 00: 1– 13. Available from: https://doi.org/10.1111/eve.13777