Vitamin E Could Support Immune Function in Horses with PPID

In addition to its role as one of the body’s most powerful antioxidants, vitamin E also supports the horse’s immune system. This is especially important in horses diagnosed with pituitary pars intermedia dysfunction (PPID, equine Cushing’s disease), which appear more prone to infection than other horses.

According to the American College of Internal Veterinary Medicine, “in cases of PPID, the hypothalamus and pituitary gland, which reside at the base of the brain, fail to communicate appropriately. These glands normally communicate via nerves and bloodflow to signal production and release of many hormones into the horse’s bloodstream. This failure of normal communication results in the pituitary gland becoming hyperactive, producing an excess of various hormones. The pituitary hormone that is routinely measured for diagnosis of PPID is adrenocorticotropic hormone (ACTH).”⁺

“In turn, ACTH can alter other hormone levels, most notably the stress hormone cortisol. High cortisol levels negatively affect multiple body systems, including the immune system,” said Clarissa Brown-Douglas, Ph.D., a nutritionist at Kentucky Equine Research.

Supporting previous studies on the effect of PPID on the equine immune system, veterinary researchers recently reported that horses with PPID had lower white blood cell counts compared to horses without PPID. ^*

“White blood cells, including neutrophils and lymphocytes, help fight infections. While the white blood cell counts measured in horses with PPID were still within normal limits, they were at the lower end of normal and significantly lower than non-PPID horses,” explained Brown-Douglas.

Horses with PPID appear to be at higher risk of opportunistic infections. Opportunistic infections can be defined as infections occurring in immunocompromised individuals that other horses with fully functional immune systems could ward off. For example, Rhodococcus equi, a bacterium responsible for pneumonia in foals, can be seen in some adult horses, potentially due to a compromised immune system.

“Though the researchers found clear differences in the immune responses observed between PPID and non-PPID horses, the exact mechanisms contributing to the observed immune dysfunction in PPID horses remains unclear,” Brown-Douglas said.

According to the study, “Veterinarians and owners of PPID horses may benefit from increased biosecurity precautions when caring for PPID horses, particularly in high-risk situations, such as transport, large gatherings, or competitions.”

Care should be taken in sharing equipment and enclosures, such as paddocks, tack, and buckets when travelling or away at competitions, limiting contact with unknown horses, and offering supplementary vitamin E to support the immune system.

“Nano-E, developed by Kentucky Equine Research, is a highly bioavailable source of natural vitamin E that boosts body-wide antioxidant defenses and plays a vital role in immunity,” shared Brown-Douglas.

⁺ACVIM. Pituitary pars intermedia in horses. Accessed October 23, 2020.

^*Miller, A.B., A.T. Loynachan, H.M. Bush, K.A. Hart, V.D. Barker, A.G. Campana-Emard, S.T. Grubbs, and A.A. Adams.. 2020. Effects of pituitary pars intermedia dysfunction and Prascend (pergolide tablets) treatment on endocrine and immune function in horses. Domestic Animal Endocrinology 74:106531.