Scientific and Equine Consultant

The science behind equine muscle building supplements

The science behind equine muscle building supplements

Can you really increase your horses muscle mass by feeding it the right nutrients? Yes, to an extent. The one key requirement more than what you feed is that a horse won’t develop more muscle unless it is in regular training. Even anabolic steroids work best when used in people or animals that are exercising. Of course anabolic steroids are banned from being used in horses except in rare cases where they are used for specific medical reasons. Interestingly, a study in horses showed that use of anabolic steroids in yearlings did increase muscle mass but by the time they were two year olds there was no clear difference between those that had and those that had not had anabolic steroids.

Firstly, it may help to understand what muscle is made up of. It may not be a surprise to learn that muscle is composed of a large amount of protein and that these proteins are made up of amino acids. When a horse eats a feed with protein in, the protein is broken down into its individual components, the amino acids, or short chains of amino acids known as peptides. Protein digestion takes place in the stomach. This requires an acidic environment and is one reason why long-term use of proton pump inhibitors such as omeprazole which decrease stomach acidity may interfere with normal digestive function.  Most of the digestion of protein then takes place in the small intestine by enzymes secreted by the pancreas and duodenum followed by absorption of the individual amino acids or amino acid peptides into the bloodstream.

Amino acids are classified into three-classes. Essential (indispensable), non-essential (dispensable) and conditionally indispensible. Essential amino acids are ones that cannot be made by the horse and must be obtained from the diet. Non-essential amino acids are ones that can be made by the horse. The third category of conditionally indispensible amino acids includes amino acids which the horse can normally make but which under certain circumstances may be limiting.

Essential                                            Non-Essential                                  Conditionally Indispensable

Histidine                                            Alanine                                               Arginine

Isoleucine                                          Asparagine                                        Cysteine

Leucine                                              Aspartate                                          Glutamine

Lysine                                                 Glutamate                                         Glycine

Methionine                                       Selenocysteine                                 Proline

Phenyalanine                                    Serine                                                 Tyrosine




It doesn’t matter whether the amino acid comes from oats, fish meal, alfalfa, soya, algae or carrots. The amino acid in each source is the same amino acid. What may vary is how much is present in one food source compared with another. There is nothing different to the lysine that is present in oats to the lysine that is present in for example, algae such as Spirulina. They are the same.

When it comes to the amino acid composition of muscle, Leucine and Lysine are the two amino acids present in the highest amount. Lysine is also considered to be the amino acid that if not present in sufficient amounts in the diet will limit protein synthesis (e.g. new muscle growth)[1,2,3,4,5,6]. So the first requirement for new muscle development is exercise and the second is an adequate supply of lysine.

There is a third requirement for horses to be able to grow more muscle in addition to exercise and lysine and that is sufficient energy intake. Whilst it is true that calories either in the form of oil or carbohydrate cannot be turned into muscle, if a horse is in negative energy balance, that is using up more calories each day than it is taking in from forage and feed, then it will not generate new protein (muscle). In fact, in a catabolic  (energy taken in less than energy used up) state, the horse will actually break down protein to generate energy.

So there are three basic requirements for a horse to be able to lay down new muscle: sufficient energy for the work it’s doing; regular exercise of an intensity that will cause a training effect; sufficient dietary lysine.  There is however good scientific evidence to show that the muscle growth that occurs under these conditions can be further enhanced by strategic consumption of other nutrients. There are many supplements on the market sold as muscle builders so let’s consider the common ingredients and see what evidence there is for efficacy.

1)       High Protein Diets

The idea that what we or our horses eat can influence the amount of muscle is not new. If we go back 30 years it was considered that anyone wanting to put on more muscle should consume a high protein diet. This generally consisted for human athletes of eggs, cheese, milk, fish, chicken and lean red meat. Over time, scientific studies supported the view that it was not necessary or desirable to eat all of these sources of protein, but that the same effect could be obtained from consuming a purified source of protein. This lead to the widespread use of whey protein extracts (protein extracted during cheese making). This gave the same effect as eating a high protein diet but the volume of food that needed to be consumed was much less as the protein was purified. More recently, studies demonstrated that it was not necessary to consume all the different amino acids and not even all 9 of the essential amino acids but only three; the so called branched chain amino acids (BCAA) leucine, isoleucine and valine [7]. Even more recently, studies have shown that the muscle enhancing effect of BCAA is almost entirely due to one essential amino acid; leucine. Thus, the recommendations for athletes who want to increase their muscle mass is to consume leucine or its metabolite, HMB (hydroxymethylbutyrate)[7].

2)       Creatine

Creatine is a key component of many human muscle building supplements and for very good reason. A very large number of controlled scientific studies in people have demonstrated its efficacy. Many equine muscle building supplements also contain creatine. Creatine is high in red meat and perhaps not surprisingly, being a herbivore, the horse has no mechanism in its digestive system to absorb creatine. Thus, in studies where horses have been fed creatine it does not change the muscle creatine levels and it is barely even absorbed. If you are buying supplements with creatine in then you are wasting your money. [8, 9, 10]

3)      Gamma-oryzanol

Gamma-oryzanol is a natural substance that occurs in the oil within rice. Gamma oryzanol is marketed as a natural steroid. At one stage it was listed by the FEI as a prohibited substance but is currently permitted. There are currently only two studies in human subjects and neither found any effect of feeding gamma oryzanol on muscle mass [11, 12]. There are few studies of gamma oryzanol in horses. One study found that feeding 2g gamma oryzanol per day for 31 days did not change blood testosterone levels [13] and no studies have shown any evidence of enhanced muscle growth.

4)     Spirulina (blue-green algae) 

Blue-green algae are photosynthetic organisms that occur in fresh and salt water habitats. They range from small, single-celled forms to complex multicellular forms, such as the giant kelp. They contain a high proportion of protein (around 2/3rds) and all 9 essential amino acids. They are also suggested to be a good source of B vitamins, but there is debate over the bioavailability of B12 in Spirulina.  Spirulina is also high in iron and this should be considered when feeding to horses as iron excess is much more common in horses than iron deficiency given that horses have no way of excreting iron ingested into the body. Blue-green algae that are free of contaminants such as microcystins, toxic metals and harmful bacteria are considered as “possibly safe” for most people according to the US National Library of Medicine. “Contaminated blue-green algae can cause liver damage, stomach pain, nausea, vomiting, weakness, thirst, rapid heartbeat, shock, and death. Don’t use any blue-green algae product that hasn’t been tested and found free of mycrocystins and other contamination.” [14] Blue-green algae may be a concentrated form of protein but the amino acids are no different to those in forages or cereals. In fact the proportions of the different amino acids is very similar to that of forages or cereals such as oats and the US National Library of Medicine also makes the following comment:  “You may have been told that blue-green algae are an excellent source of protein. But, in reality, blue-green algae is no better than meat or milk as a protein source and costs about 30 times as much per gram” (14). 200g of oats will contain the same range and levels of amino acids as 100g of Spirulina and be a lot cheaper! Spirulina is also the main ingredient in Equitop Myoplast.

5)       BCAA (leucine, isoleucine and valine)

BCAA make up around one third of the protein in muscle. Leucine, isoleucine and valine are three of the nine essential amino acids because they must be obtained from the diet as they cannot be synthesised from other components in the diet. In human medicine and sport there is an increasing number of scientific studies which suggest that of the three BCAA, leucine may play the most important role in stimulating protein synthesis [15].  In human sport, BCAA have been shown to aid in recovery processes from exercise such as stimulating protein synthesis, aid glycogen replacement, delaying the onset of fatigue and helping maintain mental function in aerobic-based exercise (see review 15). In horses, one study has shown a reduction in blood lactate after exercise. Two studies which fed either 22.5g, 1h before exercise [16] or 33g three times a week [17] both failed to show any benefit but neither of these studies followed the current recommendations for human athletes of 90mg BCAA/kg/day of BCAA (equivalent to 45g per day for a 500kg horse).

6)     HMB (B-hydroxy B-methylbutyrate)

HMB is a metabolite of the amino acid leucine. That is if leucine is consumed in food, it will be “processed” in the intestinal tract, muscle and finally liver to release HMB. HMB is present in small amounts in some feeds that horses consume naturally, such as alfalfa. HMB is thought to work by speeding up the process by which muscle is able to repair and regenerate itself following exercise. Some of the effects of HMB that have been clearly established in scientific studies in human subjects include increasing muscle strength and power and speeding recovery from exercise by reducing muscle damage. In horses, feeding 10-15 g/day HMB for 6-32 weeks has been reported to improve endurance, reduce muscle damage, aid maintenance of bodyweight, increase red blood cell number and win rate in racing [18, 19, 20].


In order for a horse to increase its muscle mass it must be receiving sufficient energy for the work it’s doing, be undertaking regular exercise of an intensity and frequency that will cause a training effect and be receiving sufficient dietary lysine. There is no evidence to support the use of a creatine or gamma-oryzanol in equine muscle building products. High protein diets may influence muscle development but feeding a high protein intake increasing the stress on the liver and kidneys as these are the organs responsible for metabolising and excreting excess protein as this cannot be stored. Spirulina is a concentrated source of protein but the same amount of amino acids would be delivered by 2-3 times the weight of cereals or forages. At present, the only feed ingredients considered to contribute to increasing muscle mass are leucine and or HMB [15].


1)      Breuer, L.H., Kasten, L.H. and Word, J.D. (1970) Protein and amino acid utilization in the young horse. Proceedings of the 2nd Equine Nutrition Research Symposium, 16-17.

2)      Hintz, H.F., Schryver, H.F. and Lowe, J.E. (1971) Comparison of a blend of milk products and linseed meal as protein supplements for young growing horses. J. Anim. Sci. 33, 1274-1277.

3)      Potter, G.D. and Huchton, J.D. (1975) Growth of yearling horses fed different sources of protein with supplemental lysine. Proceedings of the 4th Equine Nutrition and Physiology Symposium. 19-20.

4)      Ott, E.A., Asquith, R.L. and Feaster, J.P. et al (1979) Influence of protein level and quality on the growth and development of yearling foals. J Anim Sci, 49, 620-628.

5)      Graham PM, Ott EA, Brendemuhl JH and TenBroeck SH. The effect of supplemental lysine and threonine on growth and development of yearling horses. J Anim Sci. 1994 Feb;72(2):380-6.

6)      Graham-Thiers PM and Kronfeld DS. Amino acid supplementation improves muscle mass in aged and young horses. J Anim Sci. 2005 Dec;83(12):2783-8.

7)      Campbell, B., Kreider, R.B., Ziegenfuss, T., La Bounty, P., Roberts, M.,  Burke, D., Landis, J., Lopez, H. and Antonio, J. (2007) International Society of Sports Nutrition position stand: protein and exercise. J. Int. Soc. Sports Nutr. 4, 1-8.

8)      Sewell, D. and Harris, R.C. (1995) Effect of creatine supplementation in the Thoroughbred horse. Equine Vet J Supp. 32, 239-242.

9)      Schuback K, Essén-Gustavsson B and Persson SG. Effect of creatine supplementation on muscle metabolic response to a maximal treadmill exercise test in Standardbred horses. Equine Vet J. 2000 Nov;32(6):533-40.

10)   D’Angelis FH, Ferraz GC, Boleli IC, Lacerda-Neto JC and Queiroz-Neto A. Aerobic training, but not creatine supplementation, alters the gluteus medius muscle. J Anim Sci. 2005 Mar;83(3):579-85.

11)   Fry AC, Bonner E, Lewis DL, Johnson RL, Stone MH and Kraemer WJ. The effects of gamma-oryzanol supplementation during resistance exercise training. Int J Sport Nutr. 1997 Dec;7(4):318-29.

12)   Eslami S, Esa NM, Marandi SM, Ghasemi G and Eslami S. Effects of gamma oryzanol supplementation on anthropometric measurements & muscular strength in healthy males following chronic resistance training. Indian J Med Res. 2014 Jun;139(6):857-63.

13)   Mosseler, A., Licht, S., Wilhelm, L and Kamphues, J. (2010) Can oral intake of gamma-oryzanol (experimentally given orally as pure substance) result in doping relevant testosterone levels in urine of mares and geldings?  In: The impact of nutrition on the health and welfare of horses; Wageningen Press. pages 293-294.

14)   http://www.nlm.nih.gov/medlineplus/druginfo/natural/923.html Accessed 27/06/2015

15)   Campbell, B., Kreider, R.B., Ziegenfuss, T., La Bounty, P., Roberts, M.,  Burke, D., Landis, J., Lopez, H. and Antonio, J. (2007) International Society of Sports Nutrition position stand: protein and exercise. J. Int. Soc. Sports Nutr. 4, 1-8.

16)   Stefanon, B., Bettini, P. and Guggia, P. (2000). Administration of branched-chain amino acids to Standardbred horses in training. Journal of Equine Veterinary Science 20: 115–119.

17)   Casini, L., Gatta, L. and Magni, B. (2000) Effect of prolonged branched-chain amino acid supplementation on metabolic response to anaerobic exercise in Standardbreds. Journal of Equine Veterinary Science 20: 120–123.

18)   Nissen, S., Fuller, J. and Rathmacher, J. (1997). ß-hydroxy ß-methylbutyrate (HMB) supplementation in training horses. Metabolic Technologies Bulletin, Ames, Iowa.

19)   Miller, P. and Fuller, J.C. (1998). The effects of supplemental ß-hydroxy-ß-methylbutyrate (HMB) on training and racing Thoroughbreds. Abstract from the 17th Annual Meeting AESM, Leesburg, VA, p.13.

20)   Ostaszewski, P., Kowalska, A., Szarska, E., Szpotański, P., Cywinska, A. Bałasińska, B. and Sadkowski, T. (2012)  Effects of β-Hydroxy-β-Methylbutyrate and γ-Oryzanol on Blood Biochemical Markers in Exercising Thoroughbred Race Horses. J. Equine Vet. Sci. 32(9), 542-551.

Date: June 27, 2015