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  • Ascorbyl Monophosphate: A Stable Form of Vitamin C

    Did you know that there is more than one form of vitamin C? You may be wondering: if this is the case, which one is best for my horse?

    Vitamin C is a naturally occurring vitamin that decreases oxidative stress and provides support for several bodily processes, such as collagen synthesis and immune function. Research has found that it is vital for the support of several conditions, including recurrent airway obstruction, exercise induced pulmonary hemorrhage, and joint damage.

    As it is a water-soluble molecule, it can work both inside and outside of the cell to prevent damage. A horse that is healthy, on fresh forage, and has a functioning liver shouldn’t need to be supplemented with vitamin C.

    Whilst horses can produce their own vitamin C in the liver, prolonged stress or a compromised immune system can reduce plasma concentrations due to increased utilization of the vitamin. Direct links have been made between poor performance and reduced vitamin C plasma concentrations. Furthermore, foals are dependent on their mothers to provide them with vitamin C until weaning. As it is beneficial for skeletal development and respiratory health, it can be very detrimental to the foal if the mare is deficient. In these instances, it can be beneficial to supplement it – but which type is best?

    Types of vitamin C

    If you have ever looked at supplements containing vitamin C before, you may have noticed that most of them contain it in the form of ascorbic acid. Ascorbic acid is the form of vitamin C that is often found in fruit and vegetables. Whilst it provides antioxidant benefits, it has been found that ascorbic acid is not the most bioavailable form of vitamin C, and is difficult for the horse to absorb compared to humans, reducing its efficacy. Furthermore, it is very unstable and can degrade rapidly in storage due to heat, light and moisture.

    The other type of vitamin C that you may see in the ingredient lists, is ascorbyl monophosphate. This is a more stable form of vitamin C and is more effective in raising plasma concentrations than ascorbic acid. This means that your horse will receive a greater benefit when receiving ascorbyl monophosphate compared to ascorbic acid.

    Ascorbyl monophosphate is also more bioavailable and easier for the horse to absorb. It is absorbed by passive diffusion in part of the gastrointestinal tract called the ileum, before quickly entering the plasma and extracellular fluid. It is thought that this rapid absorption could be a result of carriers or co-factors in the matrix of ascorbyl monophosphate which facilitate the uptake of vitamin C in the ileum. Studies have found that not only does ascorbyl monosphate increase plasma concentration more than ascorbic acid, but also that there are differences in uptake between individuals when supplemented by ascorbic acid.

    How much does my horse need?

    As horses are able to synthesize vitamin C in the liver, a horse that is receiving fresh forage, is in light work, and has no health issues should not need to be supplemented with vitamin C.

    Research recommends that the daily intake for horses in hard work or competition should be around 1500mg per day to promote exercise performance recovery. Older horses should receive around 3000mg per day, whilst horses that have health conditions, reduced immune function or require extra support should receive around 5000mg per day.

    All of our supplements that include vitamin C, such as RespirAid DHA, contain it in the form of ascorbyl monophosphate, to ensure that the horse is receiving the optimal benefits of the important antioxidant.



    Castro, F. O., Torres, A., Cabezas, J., & Rodríguez-Alvarez, LL. (2014). Combined use of platelet rich plasma and vitamin C positively affects differentiation in vitro to mesodermal lineage of adult adipose equine mesenchymal stem cells. Research in Veterinary Science, 96(1), 95–101. https://doi.org/10.1016/j.rvsc.2013.12.005

    Deaton, C. M., Marlin, D. J., Smith, N. C., Roberts, C. A., Harris, P. A., Kelly, F. J., & Schroter, R. C. (2003). Pulmonary bioavailability of ascorbic acid in an ascorbate-synthesising species, the horse. Free Radical Research, 37(4), 461–467. https://doi.org/10.1080/1071576031000068627

    Geor, R. J., Harris, P. A., & Coenen, M. (2013). Equine applied and Clinical Nutrition: Health, Welfare and Performance. Saunders Elsevier.

    Gupta AK, D. R. (2014). Effect of oral supplementation of vitamin C and exercise on plasma vitamin C status in Marwari horses. Journal of Veterinary Science & Technology, 05(02). https://doi.org/10.4172/2157-7579.1000169

    Kirschvink, N., Moffarts, B. de, & Lekeux, P. (2008). The oxidant/antioxidant equilibrium in horses. The Veterinary Journal, 177(2), 178–191. https://doi.org/10.1016/j.tvjl.2007.07.033

    Ralston, S., & Stives, M. (2012). Supplementation of ascorbic acid in weanling horses following prolonged transportation. Animals, 2(2), 184–194. https://doi.org/10.3390/ani2020184

    Snow, D. H., & Frigg, M. (1990). Bioavailability of ascorbic acid in horses. Journal of veterinary pharmacology and therapeutics13(4), 393–403. https://doi.org/10.1111/j.1365-2885.1990.tb00794.x

    Vasconcelos Franco, J. S., Chaveiro, A., Góis, A., & Moreira da Silva, F. (2013). Effects of α-tocopherol and ascorbic acid on equine semen quality after cryopreservation. Journal of Equine Veterinary Science, 33(10), 787–793. https://doi.org/10.1016/j.jevs.2012.12.012

    Winther, K., Kharazmi, A., Hansen, A. S. V., & Falk-Rønne, J. (2012). The absorption of natural vitamin C in horses and anti-oxidative capacity: A randomised, controlled study on Trotters during a three-month intervention period. Comparative Exercise Physiology, 8(3–4), 195–201. https://doi.org/10.3920/cep12006

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