Updated: Apr 19
It continuously shocks me how very simple nutrition tools can identify the root of so many equine diet problems. The number I'm going to talk about today is one such simple tool. It's the first chapter in the story about your horse's ideal feeding program. It lays the framework for which everything else is built around a balanced equine diet. It's called "Intake as a percentage of ideal body weight", and I want to show you how cool it is and useful it can be.
What is this Number?
The number is, simply put, the amount of feed that a horse requires each day to meet it's basic needs. The reason that "Intake as a Percentage of Ideal Body Weight" (I%IBW) is so useful is because it gives us a place to start. It's a platform from which the entire diet is delicately balanced. If you knew NOTHING about a horse- not it's history, its previous diet, its activity level, or its general metabolism - you would start by feeding that horse 2% of it's ideal body weight. The reason that we start with 2%, is because that is what research has agreed is the average horse's daily consumption rate to meet its needs. Within this number is also an assumption of how much a horse will "choose" to consume when left to their own devices. The most simple example to illustrate this is a herd of horses ranging on unlimited, average quality forage. The herd, with a range of ages, sizes, and preferences, will each consume about 2% of their ideal body weight in dry matter on average. For example, a 1,000 lb mature horse in good health will consume 20 lbs of dry matter per day (22.2 lb hay or 33.3 lb of pasture As-Fed), or roughly 3.65 tons of dry matter per year (7,300 lbs). *For those of your familiar with the difference between dry matter and as-fed, know that 10% moisture for hay and 40% moisture for pasture are generously assumed and must be accounted for when calculating final amounts to feed.
This very simple number can identify some really big problems rooted in overconsumption or underconsumption. I have several examples for you.
Example #1 (this has happened several times in the last couple months): The owner calls and their first concern is that the horse can't maintain a topline. The horse will not gain weight and looks unthrifty. Within the first few minutes of the consult, after calculating the I%IBW, we notice that the horse simply isn't eating ENOUGH! The horse is eating 1.7% of it ideal body weight rather than >2.3% of its ideal body weight. I see this often with families getting their kid's first big warmblood after owning a pony. Or maybe an owner with a horse at a boarding facility that doesn't understand what the horse is really eating each day. I love it when this happens, because the answer is usually very straight forward and we can see results very quickly by simply feeding more.
Example #2: A horse at high risk for laminitis is having a hard time losing weight. Upon calculation of I%IBW, we realize that the horse is eating FAR too much for it's size and activity level of a high quality forage. You can't feed a fat horse 2.6% of it's IBW in a high quality forage and expect it to lose weight. Instead, you can feed a lower quality, low Relative Feed Value forage at <2% of its ideal body weight (not its current fat weight), and see some results.
Example #3: An owner is complaining about their horse not finishing their hay and/or pellets each day and worries that there is something wrong. The I%IBW very quickly tells me that the horse isn't ill or ulcer-ful, it's just plain FULL and can't eat more! If you put 3% of an average horse's weight in front of it each day, it's probably not going to eat all of it.
Example #4: An owner is concerned about their chronically ulcerey horse. Well, understanding the I%IBW tells us what quality of hay needs to be fed to increase time chewing and prevent gastric ulcers, because the bridge between weight management and increased time chewing is forage quality.
Example #5: I've also used this number to estimate how much pasture is contributing to a horse's diet. Pasture intake is a seriously difficult number to predict even for researchers. There are far too many factors involved, and measuring how much your horse bites, chews, and swallows each hour would daunt even the most dedicated grad student. However, if we use some reverse math, we can subtract the hay, feed and supplement intake from an assumed I%IBW and get a fairly rough estimate of how much pasture is contributing to the diet. For example, if a 1,000 lb horse is assumed to eat 2.2% of IBW and we know that he's eating 10 lb hay and 4 lb feed/supplements, then we can subtract 14 lbs from 22 and get 8 lbs of pasture per day. That's more than 1/3rd of the horse's diet, so therefore quite significant. Did I mention that the horse can get that in just 4-6 hours of pasture grazing?
With experience and maybe some guidance, we start manipulating "Intake as a Percentage of Ideal Body Weight" depending on the nutrition goals. First off, does the horse need to gain weight? Lose weight? or Stay the Same? The answer to that question lies in your horse's body condition score. Go to "Keeping Score: A Xanax for Your Equine Nutrition Anxiety" to learn more about that. Note that the number we use is the horse's IDEAL weight. Finding the IDEAL weight can trip up a horse owner using this for the first time, so if that's you, don't worry about it. Just use your horse's current actual weight using a weight tape and read "Frustrations About Weight". Remember, this is a CRUDE tool.
For a horse that needs to lose weight, we generally shoot for <1.8% IBW. Some talk about feeding as low as 1.2% of IBW, but that makes me nervous, because another set of problems can arise such as stall vices and gastric ulcers. Researchers have also learned that severe feed restriction for metabolic horses can be counterproductive. We are all familiar with the experience of very restrictive human dieting creating the boomerang effect. This is because hormones are involved and they are far harder to predict than calories in/calories out. Therefore, I try very hard not to go below 1.5% of IBW even for obese horses using forage quality as my bridge.
For a horse to stay the same weight, we generally shoot for 1.8-2.2% of IBW. We balance all of the pasture, hay, feeds and supplements around that number. For a horse to gain weight, we'll balance a diet at >2.2% of IBW. We can go all the way to 3% of IBW, but that's mostly limited to minis and ponies overstuffing themselves. Of course, it's never as simple as I make it out here, but once again, this is a crude tool that get's the ball rolling in the right direction.
Calculating this Number
In order to calculate your horse's "Intake as a Percentage of Ideal Body Weight" (I%IBW) you need to know 2 numbers; 1) the total amount of feed going down your horse's throat each day in pounds and 2) their ideal body weight. Let's break down each piece of this equation and describe what I%IBW means.
I%IBW = (Daily Total Pasture + Total Hay + Total Feed + Total Supplements in Pounds) / Ideal Body Weight in Pounds
Below are the three tools that you need to create this number; a scale, an app, and a measuring tape. I prefer a digital fish scale for weighing hay flakes and feed scoops. Find your horse's current daily intake by weighing your hay flakes and adding that to the total amount of feed fed per day (don't add water to this mix if you soak pellets). Then, use the Healthy Horse App by the University of Minnesota to calculate your horse's current and ideal weight. For this app, you'll need a fabric tape from a craft store that is no shorter than 80 inches. If you have a regular weight tape around, use that with body condition scoring to estimate your horse's ideal weight. Need help? Schedule a Free 15 Minute Discovery Call with On Course Equine Nutrition's nutritionist to learn more about private consulting.
Summarizing Intake as a Percentage of Ideal Body Weight
Many of the tools in our equine nutrition toolbox are imperfect like a dull knife used to prep a gourmet meal. Such is the case for calculating how much TOTAL feed your horse should be eating. However, as you have seen, it can very quickly identify significant problems with a diet plan. It can also help to estimate other parts of the diet such as pasture. If you have a new horse in the barn, I would suggest using the 2% of IBW rule to start your feeding journey. A well educated equine nutrition plan always considers this number.