Do Horses Get Enough Vitamin D When Rugged Up?
These days, horses commonly have a variety of rugs in their wardrobes. Whether it's rugs for severe cold, summer sheets, fly sheets, or indoor fleeces, many horses own at least four to six different rugs for various conditions. This abundance of rugs raises the important question: do horses receive enough Vitamin D to stay healthy when they are often rugged up?
Vitamin D plays a vital role in a horse's health, particularly for maintaining strong bones and regulating calcium and phosphorus absorption through the intestines and usage in the body. Unlike humans, who primarily synthesise Vitamin D through skin exposure to sunlight, studies suggest horses do not efficiently produce Vitamin D this way, largely due to their dense coats and skin characteristics. Research conducted in New Zealand confirmed that rugging horses does not necessarily lead to Vitamin D deficiency.
The main source of Vitamin D for horses is through their diet, especially from fresh high-quality forage such as lush pasture or newly harvested hay. However, older or poorly stored hay contains lower levels of this vitamin, which can potentially impact a horse’s Vitamin D intake if pasture access is limited.
Understanding How Horses Receive Vitamin D
Horses have a natural barrier formed by their coat, which makes skin synthesis of Vitamin D through sunlight exposure quite inefficient. Even when exposed without rugs, their ability to produce Vitamin D via the skin remains minimal.
Dietary intake of Vitamin D is therefore essential, which means horses need good-quality forage or supplementation if turnout is limited or forage quality is poor. Pasture contains Vitamin D2, the plant-based form that horses absorb, while supplements might contain the animal-based Vitamin D3, which is more stable and effective in maintaining vitamin levels in horses.
Daily Vitamin D Requirements for Horses
Unlike humans who need 30 to 90 minutes of sun exposure to synthesise sufficient Vitamin D, horses require substantially more time uncovered in sunlight—around 5 to 8 hours—to even begin synthesising small amounts of Vitamin D via their skin. Consequently, their daily Vitamin D intake depends mostly on diet.
An adult horse typically requires approximately 6.6 IU of Vitamin D per kilogram of body weight daily. For example, a 500 kg horse needs about 3300 IU each day for optimal health. Growing horses may need higher amounts to support bone development.
Signs and Risks of Vitamin D Deficiency in Horses
Vitamin D deficiency is rare but can occur, especially in horses kept stabled for long periods or those with limited access to fresh pasture. Other risk factors include frequent bathing, which can remove natural skin oils necessary for any limited synthesis of Vitamin D, and living in regions with less intense sunlight during colder months.
Potential signs of deficiency include:
- Reduced appetite
- Slower growth, especially in young horses
- Physitis (inflammation of growth plates) in growing horses
- Bone demineralisation leading to weaker bones
- Poor muscle contraction and reduced performance
Is Vitamin D Poisoning a Concern?
Vitamin D toxicity in horses is uncommon. Symptoms of toxicity can mimic those of deficiency, so it's crucial not to over-supplement without veterinary guidance. Importantly, horses cannot overdose from sun exposure alone, as their bodies regulate Vitamin D production naturally.
Supplementing Vitamin D should always be done in consultation with a vet to ensure the correct dosage and avoid possible risks.
Practical Tips for Responsible Horse Care and Vitamin D Management
- Ensure Regular Turnout: Allow horses to spend as much time as possible outdoors without rugs, especially during sunny days, to benefit from natural Vitamin D sources.
- Provide High-Quality Forage: Feed horses fresh pasture or good-quality hay harvested and stored properly to retain Vitamin D content.
- Limit Over-Bathing: Avoid frequent washing that removes natural skin oils necessary for minor Vitamin D synthesis.
- Consult Your Vet: Regularly check your horse’s nutritional status and consult a vet before adding any supplements to their diet.
- Be Mindful in Winter or Northern Locations: In areas with limited sunlight or during winter months, increased attention to dietary Vitamin D is crucial.
Conclusion
While rugging horses is an effective way to protect them from harsh weather, it does not significantly impact their Vitamin D status since they do not primarily synthesise this vitamin through their skin. The critical factor in ensuring adequate Vitamin D levels is a diet rich in quality forage and regular turnout. Responsible management, including appropriate supplementation guided by a vet and good pasture access, ensures horses remain healthy and strong regardless of the rugs they wear.
