Vitamin D for Respiratory Health in Horses

Recent research describes unique vitamin D dynamics in horses and confirms that the nutrient plays an important role in bone health. Studies indicate that the benefits of vitamin D extend far beyond basic bone health and play a role in boosting immune function and squelching inflammatory airway disease (IAD) in horses.

“As the name implies, IAD is caused by inflammation of the lower airways, and is similar to asthma in humans. There are many, and often multiple, causes of IAD including environmental irritants, bacteria, and viruses. Young horses are exposed to many of these airborne particles that can cause airway inflammation,” said Peter Huntington, B.V.Sc., M.A.C.V.Sc., director of nutrition at Kentucky Equine Research (Australia).

Once the airways become inflamed, clinical signs can develop such as a mild, intermittent cough; nasal discharge; mucus accumulation in the trachea; and poor athletic performance.

Until now, key management strategies for horses with IAD included environmental management such as low-dust bedding and feeds, maximal turnout, and anti-inflammatory and bronchodilator medications. Now, veterinary researchers** are suggesting that vitamin D may also play a role in helping horses with IAD.

“Human studies have previously documented a strong association between vitamin D deficiency and bronchial asthma, a condition similar to IAD,” said Daniela Bedenice, D.V.M., a respiratory specialist at Cummings School of Veterinary Medicine at Tufts University in North Grafton, Mass.

To determine if a similar association between low vitamin D levels and IAD exists in horses, Bedenice and colleagues measured vitamin D levels in 23 horses with IAD and 13 controls.

“Although circulating blood levels of vitamin D were significantly lower in horses with IAD, research has not yet established if this is a cause or effect of the condition,” relayed Huntington.

Decreased vitamin D levels were also associated with an increased number of neutrophils, which are specialized white blood cells that fight infection.

Other studies*** suggest that vitamin D might have antimicrobial properties and that vitamin D supplementation could help fight common infections, such as influenza. Although the researchers stated, “…it would be premature to claim that vitamin D has an effect on…infection,” the possibility of reducing IAD through simple vitamin D supplementation is exciting.

Main sources of vitamin D acquisition for horses are diet and exposure to sunlight. Be aware, too, that the daily recommended intake of vitamin D is 6.6 IU/kg body weight, and signs of toxicosis include depression, anorexia, and limb stiffness. Always discuss potential dietary changes, including supplementation, with a veterinarian and equine nutritionist.

In addition to vitamin D, the anti-inflammatory long-chain omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are also recommended as a nutritional supplement for IAD. These omega-3s are found in EO•3, a palatable marine-derived product that is top-dressed on the feed.

*Hymøller, L., and S.K. Jensen. 2015. We know next to nothing about vitamin D in horses! Journal of Equine Veterinary Science. 35:785–792.

**Bedenice, D., et al. 2015. The relationship between serum 25-hydroxy vitamin D levels and inflammatory airway disease (IAD) in horses. In: Proc. American College of Veterinary Internal Medicine Forum. Indianapolis, Ind.

***Bruce, D., J.H. Ooi, S. Yu, et al. 2010. Vitamin D and host resistance to infection? Putting the cart in front of the horse. Experimental Biology and Medicine (Maywood). 235(8):921-927.