Do Blanketed Horses Get Enough Vitamin D?

Researchers determined that blanketing does not appear to impact horses’ vitamin D status.

Photo: Courtesy Dr. Sara Azarpeykan

Many horses today have wardrobes that rival those of their owners—winter rugs, turnout sheets, rain covers, fly gear, and more. We know these blankets can help keep horses warm, dry, and fly-free, but how they impact some aspects of horse health remain unclear. Take vitamin D, for example: Horses need sunlight to synthesize this vitamin that’s important for bone health. So does blanketing affect their ability to produce it? That’s what a research team from New Zealand recently tried to find out.

Sara Azarpeykan, DVM, PGDip, a PhD candidate at Massey University, in Palmerston North, and colleagues presented their study results in a poster presentation during the 2015 American College of Veterinary Internal Medicine Forum, held June 4-6 in Indianapolis, Indiana.

Vitamin D is key to keeping a horse’s body functioning properly. It helps maintain plasma calcium concentrations and promotes calcium and phosphorus absorption from the intestine. It also helps mobilize stored calcium, with an indirect impact on bone mineralization.

Researchers know that good amounts of vitamin D exist in sun-cured forages. Therefore, horses that consume good-quality hay and have at least some outdoor exposure should be getting plenty of vitamin D. Still, “Equine vitamin D metabolism and factors influencing vitamin D synthesis remain poorly understood,” said Azarpeykan.

She explained that human skin’s ability to synthesize vitamin D3 can be influenced by factors including hair and skin pigmentation, season, latitude and altitude, type of clothing, and sunlight exposure.

Many horses in New Zealand spend much of their time turned out with blankets on, so the researchers sought to determine whether such horses had lower blood serum concentrations (to determine whether the animal has enough vitamin D) than unblanketed horses in similar living situations.

The team employed 21 mature horses—five of which wore blankets with neck covers—living on pasture and consuming grass and hay, when needed. The researchers collected and evaluated blood and pasture samples monthly for 13 months. Specifically, said Azarpeykan, they looked for levels of 25-hydroxyvitamin D2 and D3 (25OHD2 and 25OHD3, respectively) and 1,25-dihydroxyvitamin D (1,25[OH]2D)—all forms vitamin D—in the serum.

Azarpeykan said the study suggest vitamin D3 doesn’t appear to be synthesized in horses’ skin and, as a result, stressed the importance of a horse’s diet in ensuring adequate vitamin D levels.

Photo: Courtesy Dr. Sara Azarpeykan

Upon reviewing their results, the team determined that:

  • 25OHD2 was the most abundant form detected;

  • There was no 25OHD3 detected in any samples;

  • There was no differences in serum 25OHD2 and 1,25(OH)D2 levels between blanketed and unblanketed horses;

  • The pasture had high vitamin D concentrations that exceeded the minimum daily recommended intake for horses; and

  • 25OHD2 and pasture vitamin D concentrations “directly correlated” to the amount of sunshine each month had.

“These results suggest that blanketing does not affect the ability of mature horses at pasture to synthesize vitamin D3 in skin,” Azarpeykan concluded.

She also noted that these results suggest vitamin D3 doesn’t appear to be synthesized in horses’ skin and, as a result, stressed the importance of a horse’s diet in ensuring adequate vitamin D levels.

About the Author

Erica Larson, News Editor

Erica Larson, News Editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado, and enjoys photography in her spare time.