How Much Do You Know About Your Horse’s Diet?
by Stormy May

Most horse owners are mystified by trying to decide what their horse should be eating. Besides the debate over what hays are best, there are enough equine grains and other supplements on the market to feed a small (or medium sized!) country. Analyzing your horse’s ration scientifically might seem like a smart choice but even then, it seems that the more you read about it the less you know what to believe.

(Note: For those of you who have the Pony Club USPC B/HA/A manual, there is a worksheet that shows how to balance a ration. Unless you’re a math whiz it might take you quite a while to figure out. What is useful in the manual is the several pages of nutritional value charts. If you don’t have the manual, I’ll guide you to some places where you can find these values online.)

The BEST online resource I’ve seen for figuring out equine rations is on the Purdue University Cooperative Extension website at:
http://www.ces.purdue.edu/extmedia/AS/AS-429.html

I’m going to walk you through their method. Please make sure you visit the webpage above either before you finish reading this article or before you sit down to calculate your own horse’s ration.

Let’s start with figuring out what your horse needs. Please keep in mind that for all these numbers to follow, they are averages. This isn’t rocket science, use the numbers as guidelines not absolutes. Even more important than the numbers are the questions: is your horse currently a good weight?, is s/he healthy?, is there at least a bit of shine to the coat?, does s/he have enough energy to do the work asked?

So, on to our theoretical horse:

Salsa is a 12 year old, 1,000 lb TB/QH cross gelding in moderate work. He is in good condition on his current diet of orchard grass and rye grass hays and is a relatively easy keeper. He lives in a large corral with 4 other horses (no grass growing) so the amounts he eats we’ll calculate as one fifth of what all 5 horses eat.

Right now, Salsa receives approximately 10 pounds of orchard grass hay in the morning, 8 pounds of ryegrass hay for lunch, and 10 pounds of orchard grass hay in the evening which totals out to:

20 lbs orchard grass hay per day
8 lbs ryegrass hay per day

A) Find your horse’s daily requirements. (Tables 1 and 2 on the Purdue webpage)
Since they give amounts for 880lb and 1,100lb horses and Salsa is 1,000lbs, I’m going to go back to what I learned in my junior high math class and use ratios to figure out what the numbers should be for Salsa. If you were never very good in math, it will get you close enough to just take an average between the 880lb numbers and the 1,100lb numbers.

Salsa needs:
Digestible Energy: 22.4 Mcal per day
Crude Protein: 1.97 pounds per day
Calcium: 27 grams per day
Phosphorus: 19 grams per day
Vitamin A 1000: 20.0 IU’s (International Units) per day

B) List ration ingredients and pounds of each in the appropriate columns.
You can start out by using the numbers in their charts but if you’d like to get even more precise, you can send your own feed in to get analyzed. Here’s a website that contains a list of labs that will test feed.

From the Purdue webpage table 4:
Late bloom orchard grass
Digestible Energy: .78 Mcal/lb
Crude Protein: .076 lb/lb
Calcium: 1.09 g/lb
Phosphorus: 1.22 g/lb
Vitamin A: 3.29 IU/lb

Since there isn’t a listing for ryegrass hay I had to do a lot of digging and finally found what I was looking for on page 62 of the “Nutritional Requirements for Horses” book available to read for free online at www.nap.edu (from their main page, do a search on “horses” and then under the “Nutritional Requirements for Horses” heading click on “READ Free Online.”

Ryegrass hay
Digestible energy: .71 - .83 Mcal per pound
Crude protein: 8.8 - 10.3 percent
Calcium: .53-.62 percent
Phosphorus: .29-.34 percent
Since there’s a range, I’ll take a middle average for each value.

Unfortunately it didn’t contain a listing for Vitamin A. Since I know that Vitamin A is lost the longer the hay is stored, and Vitamin E values can vary considerably I may consider adding a Vitamin A and E supplement to Salsa’s ration depending on what my totals end up being.

C) Make sure the weight of the ration ingredients do not exceed 2-2.5% of body weight. Salsa receives approximately 28 lbs of hay for 1,000 lbs of body weight so he gets 2.8% of his body weight. I’m not too concerned about the number being high since right now Salsa doesn’t get any additional supplements, the number is an estimate between feeding 5 horses, and he’s in good condition and health.

D) To figure out the amount of nutrients Salsa is getting I do the following:

Orchard Grass Hay
Digestible Energy: 20 lbs x (multiply by) .78 Mcal/lb = 15.6 Mcals
Crude Protein: 20 lbs x .076 lb/lb = 1.52 lbs
Calcium: 20 lbs x 1.09 g/lb = 21.8 grams
Phosphorus: 20 lbs x 1.22 g/lb = 24.4 grams
Vitamin A: 20 lbs x 3.29 IU/lb = 65.8 IU’s

Ryegrass Hay (since the many of the values for the ryegrass hay were in percentages
rather than grams or pounds, we’ll have to take a couple of extra steps...)
Digestible Energy: 8 lbs x .77 Mcal/lb = 6.16 Mcals
Crude Protein: 8 lbs x 9.55% (remember 9.55% = .0955) = .764 lbs
Calcium: 8 lbs x .58% = .0464 lbs (if you remember that 16 oz = 1 pound and 1 oz = 28.35 grams then you can convert .0464 lbs to 21.0 grams)
Phosphorus: 8 lbs x .32% = .02 lbs (9.07 grams)

(If he were getting a grain ration, I would add it here after getting information from the feed tag and calculate it out just like I am doing for the hays.)

E) Total the amounts of nutrients for the two hays fed:
Digestible Energy: 15.6 Mcals + 6.16 Mcals = 21.76 Mcals
Crude Protein: 1.52 lbs + .764 lbs = 2.284 lbs
Calcium: 21.8 g + 21.0 g = 42.8 g
Phosphorus: 24.4 g + 9.07 g = 33.47 g
Vitamin A: 65.8 IU’s + ?? = over 65.8 IU’s

F) Compare what Salsa’s getting (section E) with what his requirements are (section A).

Digestible Energy: Salsa needs 22.4 Mcal per day,
he’s getting approximately 21.76 Mcal per day (.64 Mcal deficiency)

Crude Protein: Salsa needs 1.97 pounds per day,
he’s getting approximately 2.284 lbs per day (.314 pounds excess)

Calcium: Salsa needs 27 grams per day,
he’s getting 42.8 grams per day (15.8 grams excess)

Phosphorus: Salsa needs 19 grams per day,
he’s getting 33.47 grams per day (14.47 grams excess)

Vitamin A: Salsa needs 20.0 IU’s per day,
he’s getting over 65.8 IU’s per day (45.8 IU’s excess)

I’m going to take this one step further and calculate the Calcium to Phosphorus ratio (Ca:P). Even though Salsa’s Calcium and Phosphorus intake is in excess of his requirements, I know that with these two specific minerals the most important part is that they are in balance with each other. The CA:P ratio should be from 1:1 to 3:1. If I were to feed it in a ratio that had more phosphorus than calcium, or not meet the minimum requirements of one or the other it could lead to diseases such as “big head disease”. If I divide 42.8 grams by 33.47 grams I find that Salsa is getting a 1.27:1 ratio of calcium to phosphorus which is in an acceptable range. If your horse gets a lot of wheat bran (high in phosphorus) be especially careful of maintaining a good ratio.

G) What this whole analysis tells me is that with the exception of Digestible Energy, Salsa is getting plenty of what he needs, in the right proportions. If I feel like I need to add a little bit more Digestible Energy (for example if he doesn’t seem to have enough energy for the work he does, if he’s losing weight, or if I increase his work load) then I’m going to look for a supplement that is high in Digestible Energy (Mcals) but doesn’t add much protein, calcium, phosphorus, or Vitamin A. Also, since he’s already getting more than 2.5% of his body weight in hay, I might look to reduce his hay as I add this supplement. I’d have to do the whole feed analysis over with the changes I’m thinking of making.

As a sample supplement, Purina’s Equine Senior’s nutrients are:
Digestible Energy: 1.225 Mcal/lb
Crude Protein: 14%
Calcium: .5 - .6%
Phosphorus: .4%
Vitamin A: 3,000 IU/lb

If I were to give Salsa just one pound of Equine Senior per day it would add 1.225 Mcals Digestible Energy (this would more than make up for his .64 Mcal deficiency). However, it would also add to the excesses that he has in all the other areas, especially protein and Vitamin A. There is probably another, more cost effective supplement that can add Digestible Energy without tipping the scales on protein, calcium, phosphorus, or other vitamins and minerals.

This article is just meant to get you started on the path to balancing your horse’s ration. What you may be most surprised at is the amount of excess nutrition your horse is getting in the form of expensive supplements. The manufacturers are banking on the fact that most horse owners feed supplements based on recommendations from friends or reading catalog descriptions rather than sound nutritional analysis.

If you wish to go further, let the Internet be your playground. You can start calculating the approximate amounts of vitamins and minerals Your horse gets (horses should have free access to a trace mineral salt block which makes the minerals a bit difficult to calculate). Just remember, not everything on the Internet should be taken as gospel, use your best judgment. See the webpage recommendations below for more great feeding-related articles.

Next Month:
Part Two - Selenium Notebook Excerpts on the necessity and dangers of selenium.

Recommended Books
Beyond the Hay Days by Rex A. Ewing

Fun and Educational Websites

The National Academies Press www.nap.edu
Read more than 3,000 books online for free including the “Nutrient Requirements of Horses, Fifth Revised Edition.” Search from the home page for “horses” and then when you find the “Nutrient Requirements of Horses, Fifth Revised Edition” click on “READ Free Online”.

Must Have Minerals http://horse.purinamills.com/bulletins/musthaveminerals.htm
A very simple, easy to understand article about the horse’s “Must- Have” minerals, reprinted from Equus magazine. Includes calcium, iron, phosphorus, selenium, sodium chloride (table salt), cobalt, copper, iodine, magnesium, manganese, potassium, sulfur, and zinc. This is HIGHLY RECOMMENDED for anyone going for their Pony Club C3, B, or HA ratings.

Basics About Feeding Horses: Reading the Feed Tag http://ianrpubs.unl.edu/horse/g1403.htm
Great webpage about reading feed tags - this page is temporarily under review but should be up again soon. We’ve posted it for future reference.

Nutrient Requirements and Balancing Rations for Horses
http://www.ext.vt.edu/pubs/horse/406-473/406-473.html
Another webpage about balancing rations, from the Virginia Cooperative Extension

Stormy May, a graduate of the United States Pony Club, and professional equine video producer, is dedicated to promoting the harmonious relationship between human and horse through quality riding instruction and educational videos, workshops, and other products. www.stormymay.com

She also produces the Horse Management Newsletter.