Ask The Vet: Equine Nutrition

Answered by, Lydia Gray, DVM, MA, SmartPak Equine
Courtesy of AAEP

Question: What is the right amount of hay to feed an adult horse per day? I have two Thoroughbreds that weight 1,000 and 1,200 lbs. Both are in their mid-teens in age. I typically put out a 40 lb bale of timothy/alfalfa in the morning and the same at night. Is that about right or is it too much? Please note that I do live in a colder climate, so my veterinarian had recommended free-choice hay in the winter to ensure they stay warm.  

Answer: Let’s take a look at the math first, then address other aspects of feeding horses since equine nutrition is both a science and an art. The rule of thumb is that horses should have at least 1% but preferably 2% of their body weight each day in forage (hay or pasture). That means:

  • Your 1000 lb horse needs between 10 and 20 lbs of hay each day
  • Your 1200 lb horse needs between 12 and 24 lbs of hay each day

Together, the horses need between 22 and 44 lbs of hay each day. If you’re putting out a 40 lb bale twice a day, on the surface, this sounds like twice as much as your horses need (i.e. 80 lbs of hay a day). HOWEVER, there are several factors that can change the basic math or contribute to more hay being required to maintain a healthy weight:

Thoroughbreds are known to be “hard keepers” with a metabolism that can burn up calories quickly, so it doesn’t surprise me that two Thoroughbreds can put away this much hay

As horses age (and yours are in their mid-teens), some begin to lose their digestive efficiency, requiring more calories and other nutrients just to stay at the same weight and energy level.

Extra hay is exactly the right thing to give to help horses stay warm in the winter, so during the cold months, additional flakes are an excellent idea.

Horses in work require additional calories and reaching for hay to provide these is another great strategy.

Now, 80 lbs of hay/day between two horses still seems a little on the high side to me, especially as part of the hay is alfalfa (what we call “ice cream” for horses in the Midwest!) and is not to be fed free-choice. Only grass hay should be available ad lib or 24/7. Are the horses wasting a lot of it? If so, then you may want to invest in an all-day hay bag or some kind of hay feeder that both protects the hay from being stepped on/laid on/defecated or urinated on AND slows down the rate of eating. There are more and more small hole hay nets and other devices to choose from every day. Just be sure to select one that is safe for unsupervised horses turned out in a group situation, like it sounds yours are.

My final word on the subject is: don’t be pigeon-holed by the numbers. If your horses look great and feel great on the amount of hay you’re giving them, then ignore what the textbooks say as long as their body condition score is close to the ideal of 5, you’re confident their diet is otherwise complete and balanced, and their annual veterinary exam pronounces them in great health!

Question: I am wondering if there are any concerns with lime in a horse’s diet or if it will interact with any medication or supplements.  

Answer: I’m not entirely clear if you’re asking about lime the citrus fruit or agricultural lime aka limestone, which is calcium carbonate. If the former, while there are compounds in grapefruit that are known to interact with certain medications in people, I am not aware of any specific concerns among lime, lemons, or oranges. If the latter, there are several different types of “ag lime” so you’ll want to make sure you’re using the right one (some are for use on pastures and in stalls and some are to complete and balance the diet). Either way, I recommend you speak with your veterinarian to make sure adding “lime” to your horse’s diet is appropriate.