The changes of the seasons affect the growth of the coat, which causes the horse to change coat twice a year. Before winter, when the days get shorter, the horse puts on a winter coat as an aid against the cold. When winter comes to an end and the days get longer, the winter coat sheds and is replaced by a summer coat. The changing of the coat is therefore seasonal and is influenced by the length of the day and daylight. A healthy coat is therefore important for regulating the horse's body temperature and protecting the skin. The quality of the coat and the duration of the shedding depends on the condition and health of the horse, but can also be influenced by nutrition.
Due to the changes of the seasons, the growth cycle of the coat is influenced and the body adapts to the environment 1. The growth cycle of the coat consists of four phases, the anagen phase, the catagen phase, the telogen phase and the exogenous phase. The anagen phase of the cycle is the phase in which hair grows and is the most active phase of the entire growth cycle 2. During the catagen phase, hair growth stops so that old hair can fall out and make way for new hair growth 2. This is followed by the exogenous phase in which the hair falls out 1. After the exogenous phase, there is a “resting” phase, or the telogen phase 2. During this phase, no growth or loss takes place, but the hair follicles prepare for the next anagen phase 2 .
Daylight, mainly the change in the amount of daylight, is perceived through the eye of the horse 3. By sensing daylight, information is recorded about the changes of the seasons 3. This information is then “translated” into electrical signals that are sent to the suprachiasmatic nucleus (SCN) in the hypothalamus 4. The SCN is seen as the biological clock and regulates the body's biorhythms. The SCN influences the production of the hormone melatonin produced by the pineal gland 5. The production of melatonin suppresses the production of prolactin, a hormone with multiple functions in the body, one of which is to regulate the cycle of the hair follicles 6.
Light is perceived through the eye. The suprachiasmatic nucleus (SCN) is stimulated by signals from the receptors in the eye. As a result, the SCN controls the pineal gland and regulates the production of melatonin. During the day, the production of melatonin is inhibited, but when it is dark, the production is stimulated. Created with BioRender.com.
When the days get shorter and the amount of daylight decreases, the body is stimulated to produce a winter coat due to the increase in melatonin and a decrease in prolactin 7. The same is true when the days get longer during the transition to spring when the amount of daylight increases. Due to the decrease in melatonin and the increase in prolactin, the hair removal process is initiated 7. The growth cycle and the thickness of the winter coat not only depend on the difference in the amount of daylight, but also on the ambient temperature. Studies show that horses in a cooler environment produce a thicker winter coat and, due to a lower temperature, also start shedding later in the season 8.
The growth of a winter coat and shedding takes energy. In addition, the growth cycle of the coat requires the necessary proteins, vitamins and minerals9. It is therefore important that the diet meets the needs and that the horse is in optimal condition. In older horses, malnourished horses, horses where the diet does not meet the needs or horses whose health is not optimal, the coat may look dull or the horse has difficulty shedding 10–13. Monitoring coat quality therefore provides valuable information about the general health and well-being of the horse 11.
The addition of supplements can support the shedding process and the growth of a healthy coat, provided the horse has no underlying health problems that require attention first. Studies show that the addition of linseed oil has a supportive effect on the horse's skin and coat 14. In addition, the fatty acids from linseed oil provide a long-lasting source of energy, which meets the increased energy needs during shedding and coat growth 15. linseed oil is regularly added to the diet because it ensures a shiny coat 15.
Research has shown that the concentration of vitamins and minerals in the coat hair changes seasonally 16. As mentioned earlier, diet and nutrients have an effect on the quality of the coat hair 9. Therefore, the addition of a vitamin and mineral supplement can support the coat growth and the shedding process 9.16.
A supplement to support the liver can also support the horse during shedding by optimizing the functioning of the liver. The liver plays an important role in protein synthesis in the body 17. In addition, the liver is also an important organ for the absorption and storage of fat-soluble vitamins and minerals, which are important for the quality and growth of the coat 17. As a result Do liver diseases also have an effect on coat quality and the shedding process 18.
Synovium Linseed Oil, Synovium Hippochol and Synovium Prefit are products from the Synovium supplement line that can support coat growth and the shedding process.
References
1. Plikus, M. v., & Chuong, C. M. (2008). Complex hair cycle domain patterns and regenerative hair waves in living rodents. Journal of Investigative Dermatology, 128(5): 1071-1080.
2. Lin, X., Zhu, L., & He, J. (2022). Morphogenesis, Growth Cycle and Molecular Regulation of Hair Follicles. Frontiers in Cell and Developmental Biology, 10:1-11.
3. Murphy, B.A. (2019). Circadian and Circannual Regulation in the Horse: Internal Timing in an Elite Athlete. Journal of Equine Veterinary Science, 76:14-24.
4. Reppert, S.M., & Weaver, D.R. (2001). Molecular analysis of mammalian circadian rhythms. Annual Review of Physiology, 63: 647-676.
5. Moore, R.Y. (1997). Circadian rhythms: basic neurobiology and clinical applications. Annual Review of Medicine, 48: 253-266.
6. O'Brien, C., Darcy-Dunne, M. R., & Murphy, B. A. (2020). The effects of extended photoperiod and warmth on hair growth in ponies and horses at different times of year. PLoS ONE, 15(1): 1-18.
7. Geyfman, M., Plikus, M. v., Treffeisen, E., Andersen, B., & Paus, R. (2015). Resting no more: Re-defining telogen, the maintenance stage of the hair growth cycle. Biological Reviews, 90(4): 1179-1196.
8. Bocian, K., Strzelec, K., Janczarek, I., Jabłecki, Z., & Kolstrung, R. (2017). Length of winter coat in horses depending on husbandry conditions. Animal Science Journal, 88(2): 339-346.
9. O'Connor, K., & Goldberg, L. J. (2021). Nutrition and hair. Clinics in Dermatology, 39(5): 412-419.
10. Kronfeld, D.S. (1993). Starvation and malnutrition of horses: recognition and treatment. Journal of Equine Veterinary Science, 13(5): 298-304.
11. Pritchard, J.C., Lindberg, A.C., Main, D.C.J., & Whay, H.R. (2005). Assessment of the welfare of working horses, mules and donkeys, using health and behavior parameters. Preventive Veterinary Medicine, 69(3–4): 265-283.
12. Ireland, J. L., Clegg, P. D., Mcgowan, C. M., Mckane, S. A., Chandler, K. J., & Pinchbeck, G. L. (2012). Comparison of owner-reported health problems with veterinary assessment of geriatric horses in the United Kingdom. Equine Veterinary Journal, 44(1): 94-100.
13. Sykes, B. W., Hewetson, M., Hepburn, R. J., Luthersson, N., & Tamzali, Y. (2015). European College of Equine Internal Medicine Consensus Statement-Equine Gastric Ulcer Syndrome in Adult Horses. Journal of Veterinary Internal Medicine, 29(5): 1288-1299.
14. O'Neill, W., McKee, S., & Clarke, A.F. (2002). Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Canadian Journal of Veterinary Research, 66(4): 272-277.
15. Warren, L.K., & Vineyard, K.R. (2013). Chapter - 7 Fat and fatty acids. In: Geor, R. J., Harris, P. A., & Coenen, M., (Eds.). Equine Applied and Clinical Nutrition. Saunders Elsevier: China.
16. Jachimowicz-Rogowska, K., Topczewska, J., Krupa, W., Bajcar, M., Kwiecień, M., & Winiarska-Mieczan, A. (2022). Seasonal Changes in Trace-Element Content in the Coat of Hucul Horses. Animals, 12(20): 1-17.
17. Trefts, E., Gannon, M., & Wasserman, D.H. (2017). The liver. Current Biology, 27(21): 1147–1151.
18. Theelen, M. J. P., Beukers, M., Grinwis, G. C. M., & Sloet van Oldruitenborgh-Oosterbaan, M. M. (2019). Chronic iron overload causing haemochromatosis and hepatopathy in 21 horses and one donkey. Equine Veterinary Journal, 51(3): 304-309.