Who supplements with vitamin C, how much do you feed and why do you supplement with it?
Horses make their own C so unless the horse is very old, no need to supplement. Is why itâs not in the comprehensive vitamin mineral supplements
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This is what I had always thought. But Iâve noticed a few people feeding it to boost immune systems. Would this work?
No. Not for people, not for horses. âBoosts immunityâ can be translated to âDoes nothing and but we can say this and not get sued.â
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âNoticed a few peopleâ doing something in the horse world means nothing unless you have an educated evaluation of who those people are.
Is this the barn fool who already foundered her horse trying to feed free choice hay? Is this your trainer pushing you to add on a pointless supplement? Is this a website selling rose hips for horses? What else do they believe in? Do you have any reason to believe they actually know about nutrition?
The vitamin C and immunity thing was believed for humans in the 1960s and 1970s (Linus Pauling?) but has since been debunked. And humans do need dietary C so they donât get scurvy. Horses donât.
Horse nutrition and therapies are where a lot of debunked or failed ideas from human care end up 20 years later.
So Iâm not amazed that someone somewhere has the idea of taking outmoded ideas about C in humans and marketing it to horses as a New Thing.
And you are right to come check it out here.
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A lot - way too many - take what they know or think they know about people, and assume it works the same for horses.
People need dietary Vit C, therefore horses do too.
People have a gall bladder to help digest fats, therefore since horses donât have a GB they canât digest fat well.
Those are the 2 common ones I see.
Vit C IS needed for a healthy immune system.
Vit C manufacturing can degrade in the older horse.
Vit C may be used faster than itâs made in the hard-working horse (which is not the majority of horses today)
so yes, there are times where supplementing may be necessary full time, or for a short while. And if itâs a shorter while, it needs to be weaned off so the body will recognize the need to ramp up production again.
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Was given a tour of a barn and I noticed all the Vitamin C supplement containers in the feed room. There were a lot so naturally peaked my curiosity. I asked the tour giver why people were feeding it and she said to âboost immune systemâ.
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Donât mind me dredging up the dead thread hereâŠ
I consulted with 2 vets on the safety of dosing Vit C. Both said safe to try. My barn owner had luck with her very complicated allergy prone horse and mentioned it when I warned her what my horse looks like if her allergies are bad that day. I tried it for a summer seasonal allergy that was an issue for my horse. My mare always responded to Benadryl but I wanted something to help prevent the reaction, if possible. Worked up Vit C suppliment to a holding dose, kept her there all summer and weaned off in late fall. Almost no allergic reaction throughout the summer during what everyone said was a bad year for allergies. Clearly this is anecdotal and not definitive proof. However if someone in a barn has tried and had good luck, makes sense why other boarders would try it too. I fed human grade fruit flavoured Vit C chewables in her grain.
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@Corky how many mg did you supplement? Research has shown that at least 3000mg is needed to make an impact, so Iâm curious what you used.
I donât like discussing dosage because I am NOT making recommendations (!!) On dosage as ppl should consult w vet.
But I used 3500mg
itâs totally ok though to say how much you used - thatâs not a recommendation for what anyone else should do 
And as I mentioned, itâs decently studied in horses that if itâs going to make an impact, you have to feed at least 3000mg, which is what you did.
I bet most vets donât know how much to supplement, even when itâs appropriate 
Adding C just for the sake of it isnât a good idea since not only do horses make their own and donât normally need supplementation, but adding it can suppress the bodyâs âdesireâ to make enough.
Being a water-soluble vitamin, it would be hard to feed so much as to cause issues, especially given how much is typically in supplements that have it
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adding another comment before anyone takes anything about my last one to mean âyou canât feed enough to cause harmâ - I have no idea if you can or canât.
You CAN take too much as a human to the point of it causing kidney stone issues. Being water soluble itâs going to eventually be processed through the kidneys. One study I read fairly recently reported that 60gm/day for long enough caused kidney issues. Thatâs WAY more than most normal people take, especially when supplements tend to be in 500mg and 1000mg doses. But ya know, there are always those who think âif some is good, more must be better!â 
I have NO idea how that translates to horses, but assume that at some point there is a thing as âtoo muchâ. I also assume thatâs not happening if using recommended doses of whatâs in typical supplements.
Yes my mare has a few of the factors for when Vit C supplementation could be helpful - namely arthritis, inflammation and allergies. Her allergies made her look like she had the flu or strangles because sheâd produce so much snot. I consulted with two vets, one with a special interest in non-pharmaseuticals who both said âsafe to tryâ. One did suggest trying concentrated echinacea. Iâm not suggesting Vit C a wonder cure, but it could help certain horses is very meaningful ways.
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