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Is a Hay-Only Diet Sufficient?

My horses eat hay pellets (either Bermuda or alfalfa mix) and in the rainy season, 5 acres of weed pasture. What vitamins or minerals should I be supplementing? Kayla

Dear Kayla,

Depending on the age and use of your horses, they are probably not getting all the nutrients they need from a hay-only diet. Even horses grazing 24/7 on high-quality pasture (which it doesn’t sound like yours is) may still require mineral supplementation depending on what part of the country you live.

So at a minimum, consider adding a multi-vitamin/mineral supplement to your horses’ diet that is balanced for the type of forage you’re providing. If you’re giving mostly Bermuda grass hay, then feed a supplement to complete and balance the vitamins and minerals for this type of forage. If you’re giving mostly alfalfa hay, then select a supplement that fills the nutritional gaps for this type of legume forage. When feeding a mix of grass and alfalfa hay, go with a supplement that balances for grass hay unless the mix is more than 50% alfalfa. Also, try to feed the same kind of hay all the time rather than switching back and forth because research has shown there is more digestive upset and risk for colic when forage is changed abruptly than grain. That’s because it’s the bugs in the back that are doing the digesting of the fiber in forages and when the source suddenly changes, they can die off—releasing toxic substances—allowing potentially harmful microbes to build up in numbers.

Another thing to consider is protein. If your horses are adults in little to no work (maintenance), then your hay may be providing enough amino acids to meet their daily requirements. However, when they’re on the weed pasture or if they do more than serve as pasture ornaments, you may want to move up to a ration balancer, which provides vitamins, minerals AND protein.

Salt should always be available, and I’m more of a loose-salt fan than traditional salt block fan because I think horses are more likely to get what they need when they don’t have to lick a rough substance. I like the new smooth, hard rock salts though. Just keep in mind they are mostly sodium chloride and don’t provide enough other minerals to meet your horses’ nutritional needs.

Lydia F. Gray, DVM, MA SmartPak Staff Veterinarian and Medical Director Dr. Lydia Gray has earned a Bachelor of Science in agriculture, a Doctor of Veterinary Medicine (DVM), and a Master of Arts focusing on interpersonal and organizational communication. After “retiring” from private practice, she put her experience and education to work as the American Association of Equine Practitioner’s first-ever Director of Owner Education. Dr. Gray continues to provide health and nutrition information to horse owners through her position at SmartPak, through publication in more than a dozen general and trade publications, and through presentations around the country. She is the very proud owner of a Trakehner named Newman that she actively competes with in dressage and combined driving. In addition to memberships in the USDF and USEF, Dr. Gray is also a member of the Illinois Dressage and Combined Training Association (IDCTA). She is a USDF “L” Program Graduate and is currently working on her Bronze Medal. Find Dr. Gray on Google+

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6 comments on “Is a Hay-Only Diet Sufficient?
  1. Jennifer says:

    I think this was a good basic article, but can you please expand on what it means, clinically and behaviourally, for a horse to have a vitamin deficiency and how that should be addressed? I hear a lot about the need for sufficient vitamins/minerals (and wholeheartedly agree) but rarely see an author or speaker talk about how imbalances (under or over!)can affect the horse. Thanks

    • SmartPak SmartPak says:

      Hello Jennifer,

      Thank you for your insightful question. Perhaps the reason few discuss the clinical signs of vitamin and mineral toxicity/deficiency is because the signs are different for each nutrient and the article would be very long and boring! If you are interested in knowing the medical conditions a horse would develop for these individual nutrients, I highly recommend the sixth edition of Nutrient Requirements of Horses, published by the NRC, as an excellent resource. In a nutshell, when a horse (or any species) is getting slightly less of a particular vitamin or mineral than their body requires for a particular life stage, they cannot function optimally. This may mean they don’t grow to their genetic potential, produce as much milk as possible for a nursing foal, or perform under saddle to the best of their ability. We believe that by providing the correct amount and ratio of these important nutrients horses will be overall more healthy resulting in overall more happy owners.

      Dr. Lydia Gray

  2. Debbie says:

    This was very helpful, and I have forwarded it to some of my horse friends,
    My 17 year old mare seems to be doing fine on a mostly fescue pasture, mineral block, left-over from winter orchard grass round bale, and a small scoop of whole oats. Of course, there are the apple wafer treats that she loves. She is a pet and we trail ride 2 or 3 times a week.

  3. Kacey says:

    Keep in mind this is written by a vet of a large supplement company. Every nutrition book I’ve read states there’s no medical reason a horse needs grain if they maintain on grass and hay. You can do more damage over supplementing a horse (especially vit A and D) than under under-supplementing. DVM Elenor Kellen put out a good book on equine nutrition and breaks everything down and is easy to understand.

  4. Kat says:

    The auther reccomended adding a ration balancer for working horses, which is more then a vitiamin supplement then a grain. I actually think it was very good, non- biased response.

  5. Carolyn says:

    I’m a little late on this one, but great article! This explains it well for hay diet horses. I’ve recommended looking at something similar for my friend’s mare as she is getting hefty even though she gets very little grain and hardly any hay (in addition to pasture turn out)!

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