Vitamin D and rugs

Today many horses have a wardrobe that is almost as big as their owner’s: winter rugs, stable rugs, rain sheets, fly sheets, etc. We know that these rugs help to keep the horse warm, dry or fly-free, but to what extent they impact other health aspects is still unclear. Take vitamin D, for example: horses need sunlight to synthesize this vitamin, which is important for bone health. So, could rugs affect vitamin D production? That’s what a research team from New Zealand was trying to find out. 


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

Vitamin D is important for a horse’s body to function properly. It is necessary for the absorption and regulation of calcium and phosphorus. It also helps release stored calcium, which indirectly impacts bone formation. Researchers know that there are good amounts of vitamin D in sun-dried foods. Therefore, horses that eat good quality roughage and are turned out regularly would get more than enough vitamin D. Still, ambiguities remain about vitamin D metabolism and the factors that influence vitamin D production in horses, Azarpeykan said. 


She explains that the ability of human skin to make vitamin D3 can be influenced by several factors such as hair, skin pigment, season, type of clothing and exposure to sunlight. Many horses in New Zealand are rugged for much of the time they spend outside. Therefore, the researchers looked at whether these horses had less vitamin D in the blood compared to horses that lived in similar conditions without a rug. They looked at the concentration of blood serum (= blood plasma without clotting proteins), which is used to determine whether an animal has sufficient vitamin D. 


The team examined 21 adult horses, 5 of which wore a rug with a neck. The horses lived at pasture and ate grass and hay. The researchers collected and analysed blood and pasture samples every month for 13 months. They specifically looked at the amounts of 25-hydroxyvitamin D2 and D3 (abbreviated 25OHD2 and 25OHD3) and 1,25-dihydroxyvitamin D (1,25(OH)D2) in the serum, which are all forms of vitamin D. 


When looking critically at the results, the team found the following: 

        25OHD2 was the most abundant form 

        No 25OHD3 was observed in the samples 

        There was no difference in the concentrations of 25OHD2 and 1,25(OH)D2 between the horses with rugs and horses without rugs 

        The pasture contained high vitamin D concentrations that were more than the recommended daily amount for horses 

        25OHD2 and the concentrations of vitamin D from the pasture were directly related to the amount of sunlight there was each month. 


“These results suggest that rug use does not affect the ability of adult horses living at pasture to make vitamin D3 in the skin,” concluded Azarpeykan. She also said that these results suggest that vitamin D3 is not produced in the horse’s skin and as a result it is all the more important that there is sufficient vitamin D in the horse’s diet. 


Tip: To find out how much vitamin D is in your roughage, you can have a roughage analysis carried out. In addition to information about the amounts of vitamins and minerals, you will also know how much energy and protein there is in the roughage. Useful information to put together a suitable diet for your horse. 


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