Your Horse Needs Vitamin D!

zorra-sunDid you know that unless you live in the Southern USA, or some other hot, sunny locale, your horse is likely Vitamin D deficient!

Yes, just like humans, horses can only make Vitamin D from the sun. Or they can ingest it from fresh, live grass (not hay). And if you live above 34 degrees North Latitude (draw a line from the middle of Los Angeles east to pass through Columbia in South Carolina – anything above that, needs Vitamin D supplementation), you and your horse cannot make enough Vitamin D from the sun anyway.

There are many other factors that can affect a horse’s Vitamin D production, and these include bathing your horse (her natural oils are needed to convert sun to Vitamin D), stalling your horse, blanketing or fly sheets covering your horse’s skin, or your horse standing under a roof for extended periods. It takes 5-8 hours of sun exposure per day for your horse to produce the required amount of Vitamin D for basic health.

According to Dr. Juliet Getty, “Horses do best when they receive at least 6.6 IU of vitamin D per kg of body weight. For an 1100 lb (500 kg) horse, this translates into 3300 IU/day. Sunlight exposure — 5 to 8 hours/day under optimal conditions – will produce this amount of vitamin D.”

Since the upper limit of Vitamin D (shown to cause toxicity) is 22,000 IU/day, I give my horses 4,000 – 6,000 IU per day, since we live in the very cloudy, rainy Pacific Northwest. The easiest way is to purchase a Vitamin D3 in liquid form and just drizzle it over your feed or supplement pellets.

Remember that Vitamin D is actually not a vitamin, but a hormone. So aside from the well-known effects of Vitamin D deficiency on bone strength and density, you also need to be aware of it’s effect on mood (depression), energy levels and immune system functioning.

One last important point to consider is that Vitamin D requires magnesium to be converted into its active form. So I also give my horses extra magnesium sprinkled over their feed. If I’m bulk-buying magnesium from the feed store (usually magnesium oxide) then I give 1 tablespoon per horse. Again, Dr. Juliet Getty has an excellent guide to magnesium supplementation for horses.

It’s very easy to find the upper limit for magnesium supplementation – just watch your horse’s poo. When their poop becomes really mushy or runny, that’s too much magnesium – simple!

While we’re on the topic, what other daily supplements do I give my horses? In addition to magnesium and Vitamin D3 I also give 1.5 tablespoons of dried seaweed, Hoffman’s Minerals, Natren Equiflora probiotics, 1.5 tablespoons of Redmond or Himalayan Salt. I sprinkle all these over 1 cup of a vitamin supplement feed. Currently, during the wet winter I’m also giving respiratory support herbs and I found the most fantastic dried herbs from a company in the UK called Wendals Herbs – I order them from

Combine that together with low sugar hay available 24/7 in slow feeders and we’ve got pretty balanced, healthy horses!

Your Horse Needs Vitamin D!

4 thoughts on “Your Horse Needs Vitamin D!

  • March 25, 2017 at 10:56 am

    Thanks for the info about the vit d3. I have been taking it myself for years and I know it changes everything in our bodies! I was taking the kind that comes from lanolin (sheep’s wool) and then I looked into a vegan source which I have been using for 2 yrs and I LOVE it (and I know it works because my levels were recently tested and they are excellent – I do take a lot more than what is suggested – ).

    What do you think of using that for horses? It’s liquid and tastes yummy! (stevia added). Definitely more expensive.

    • March 25, 2017 at 11:03 am

      Yes, that one looks fine.

  • April 17, 2022 at 11:12 am

    Thank you for your dosage guidelines. That sounds reasonable (I’m in the Pacific NW, too).

    Just wanted to throw in a thought about another vitamin the horses are deficient in…Vit C. According to what I’ve read, they consume 20g per day IF they are on pasture. If stalled, they consume around 1g. They do make some in their bodies, but with stress & toxins I’m sure the horses are deficient on the whole. I’ve started giving my horses liposomal Vit C that I make fairly cheaply and it’s amazing the difference. Less thrush. More energy. More relaxed/better mood. No more coughing. If someone has a struggling horse out there you might want to give it a try.

    • April 18, 2022 at 8:04 pm

      oh my gosh, that is a VERY good point! Thanks so much for sharing your experiences and info with us 🙂

      How do you make the liposomal Vit. C and which products/brands do you use?



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