Zinc (Zn) is an essential trace element needed to support the proper physiological function of many enzymes and proteins in the horse’s body. Enzymes are proteins that carry out reactions in the body, such as breaking down sugars and fats into energy. As an enzyme cofactor, zinc contributes, among other functions, to antioxidant protection, immune function, protein synthesis, and cell signalling. Zinc is important for foals’ skeletal development as well as normal growth and tissue health. In addition, zinc supports healthy hooves and a thriving coat and skin. For breeding horses, zinc is critical for reproductive health.
Zinc is the second most abundant trace element in horses after iron. It is present in all cells and tissues, and most of it (80–85%) is found in skeletal muscles and bones.
Benefits of zinc for horses:
Antioxidant protection
An important role of zinc is supporting the body’s antioxidant defence. Both copper and zinc are found in a key antioxidant enzyme, superoxide dismutase (SOD). Zinc also participates in regulating the production of other antioxidant enzymes (2). These enzymes convert harmful oxidants or free radical molecules into neutral, harmless compounds. Cells naturally produce free radicals, and as nutrients are broken down into energy, these radicals can damage cells over time. Through antioxidant protection, zinc helps protect against premature ageing and supports healthy tissues and cells.
Horses in heavy training and competition produce more harmful oxidants and may therefore benefit from additional antioxidant support. In one research study, heavily trained Thoroughbreds were fed an antioxidant supplement containing zinc and copper. The antioxidant capacity of horses receiving the supplement improved during the training period (3). Older horses generally have lower antioxidant enzyme levels than younger horses, and for that reason they may benefit from added zinc in the diet.
Hoof health
A proper balance between zinc and copper supports keratin synthesis. Keratin is the main protein in hooves and creates a strong hoof structure. Horses receiving sufficient zinc and copper in their diet have a lower risk of white line disease. In addition, they have a lower risk of hoof wall separation (4).
Immune function
Zinc helps immune cells respond to infections. When the body detects an infection, blood zinc levels drop as immune cells and the liver take the mineral into use. With zinc, immune cells can send signals to other cells to coordinate the immune response. A temporary drop in blood zinc during infection has been shown in horses suffering from fever and cellulitis (inflammation of the connective tissue layer of the skin) (5). However, more research is still needed to determine whether zinc supplementation benefits horses that already have an infectious disease or inflammation. At present, it is assumed that adding zinc to the diet of a horse that does not receive enough could support immune response.
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Skin wellbeing
Zinc deficiency in horses can cause skin abnormalities, such as slow wound healing. This may be due to weakened immune function. Horses whose diet contains low zinc may be more prone to rain rot (mud fever) or dermatophilosis—a type of bacterial overgrowth on the skin (Dermatophilus congolensis) that occurs in wet conditions. If immune function is reduced due to low zinc, bacteria may spread more effectively on the skin. Adequate zinc intake can support healthy skin and improve coat quality and shine.
Insulin levels and insulin sensitivity
Zinc may be beneficial for horses with metabolic problems. Studies in both animals and humans have found that low blood zinc is associated with insulin resistance and diabetes. Zinc affects insulin secretion from pancreatic cells, and adequate zinc may help ensure the correct amount of insulin is released to manage blood sugar (6). In humans, zinc supplementation has been shown to improve insulin sensitivity in obese individuals (7). The effect of zinc on insulin sensitivity has not been studied directly in horses. However, zinc is crucial for antioxidant protection, and oxidative stress is also a key factor in insulin resistance. The current assumption is that adequate zinc intake is important for horses with conditions such as metabolic syndrome or Cushing’s disease (PPID).
Joint wellbeing
Zinc is needed for producing collagen protein. Collagen is an important component of tendons, ligaments, and joints. It is also required for cartilage production. In one study, yearlings in moderate work were supplemented with a mixture of copper, zinc, cobalt, and manganese in either organic or inorganic form. After 12 weeks, horses fed organic minerals had higher markers of collagen synthesis. These horses may tolerate heavier training and may be less prone to joint wear ([8). This study also indicates that organic trace minerals may support collagen production in joints better than inorganic minerals.
Coat quality and pigment
Zinc contributes to keratin production, and keratin is the most abundant protein in hair. Keratin is responsible for creating hair structure.
In one study, horses supplemented with organic forms of zinc and copper had stronger and more elastic hair fibres than horses given the inorganic forms (9).
Zinc is also part of the enzyme tyrosinase, which produces melanin. Melanin is the pigment protein that gives skin and hair colour. Horses with a dull, faded, or fluffy coat may have too little zinc in their diet, and they may not produce enough melanin. This deficiency can be seen especially in dark chestnut, bay, and black horses, which require more melanin for dark coat colour. In these horses, changes in coat colour and quality can also be a sign of copper deficiency. For maintaining a glossy, healthy coat, the horse should receive zinc and copper in a ratio of 4:1.
Zinc and other minerals in feeding
In feeding, it is important to consider the ratios of different minerals. In particular, it is worth checking the ratios of copper, zinc, and iron. High iron levels can interfere with copper and zinc absorption, which can lead to deficiencies even when mineral intake is otherwise sufficient. Excessive iron in the diet can lead to poor liver function, anaemia (low red blood cell count), metabolic disturbances, and laminitis. If a horse eats hay or other feed that is high in iron, adding copper and zinc may help balance minerals and prevent negative consequences. In addition, high calcium levels in the feed have also been shown to reduce zinc bioavailability (11).
Zinc deficiency
Most horses receive adequate zinc from fresh grass and hay. However, imbalance with other minerals can affect absorption and lead to deficiency even if dietary zinc appears sufficient. In other words, a horse may consume enough zinc daily, but that does not necessarily mean the body absorbs enough.
Too little zinc can cause poor appetite, weight loss, or poor growth. Foals with severe zinc deficiency have been shown to have low appetite and slow growth (10). This is linked to changes in brain chemistry in the hypothalamus, which regulates food intake.
Zinc supplementation has been shown to stimulate appetite and support weight gain in humans with anorexia. Ensuring adequate zinc intake in horses may support normal appetite and healthy weight gain.
Some common signs of zinc deficiency in horses can include:
- Insulin resistance, which may show as increased drinking and urination.
- Poor sugar tolerance, recurring laminitis symptoms, or irregular fat deposits, for example along the crest of the neck.
- A dull, faded coat.
- Poor hoof quality, including cracked, brittle hooves and hooves that lose shoes easily.
- Orthopaedic diseases, including weak bone formation in foals and weak, painful joints in adult animals.
- Poor appetite leading to reduced overall condition.
- Thickened, cracked skin that is more prone to infections and/or hair loss.
References:
- Eamens, GJ et al. Skeletal abnormalities in young horses associated with zinc toxicity and hypocuprosis. Aus Vet J. 1984.
- Marreiro, DN et al. Zinc and Oxidative Stress: Current Mechanisms. Antioxidants. 2017.
- de Moffarts, B et al. Effect of oral antioxidant supplementation on blood antioxidant status in trained thoroughbred horses. The Vet J. 2005.
- Higami, A. Occurence of white line disease in performance horses fed on low-zinc and low-copper diets. J Equine Sci. 1999.
- Murase, H et al. Serum Zinc Levels and Their Relationship with Diseases in Racehorses. Int Med. 2012.
- Chausmer, Arthur B. Zinc, Insulin and Diabetes. J Am Col Nutr. 1998.
- Cruz, KJC et al. The Effect of Zinc Supplementation on Insulin Resistance in Obese Subjects: a Systematic Review. Biol Trace Elem Res. 2016.
- Dickson, Emily C. Effect of Complexed Trace Mineral Supplementation on Joint Health in Young, Exercising Horses. Texas A&M Univ Lib. 2018.
- Malgorzata, K et al. Effect of diet on mechanical properties of horse’s hair. Acta Bioeng Biomech. 2009.
- Baltaci, KA and Mogulkoc, R. Leptin and zinc relation: In regulation of food intake and immunity. Ind J Endo Met. 2012.
- Mills, CF. Dietary interactions involving the trace elements. Annu Rev Nutr. 1985.
Original article Madbarn (translation)
Written by: Dr. Priska Darani, Ph.D. Reviewed by: Dr. Christine Latham, Ph.D.
