Understanding Hay Test Results, Dry Matter and Energy

(post by Jason) Today we’re going to explore our hay test in a bit more depth. Last week I wrote at some length about measuring fibre levels and digestibility in hay and why those things might be important in terms of balancing equine diets. I want to focus today’s blog on talking about energy level and why that’s probably the most important number on your hay test. In order to do that I’m going to start with a few equine nutrition facts. Although it’s a bit unwieldy I’m going to use mostly US Standard units of measure for today’s blog post. You’ll note that the units on my hay test are in SI units. That’s because I spent the first 33 years of my life in Canada thinking, working and living in metric and to this day I still think and compute everything in metric first. Sorry.

The average horse will eat roughly 2% of it’s body weight in free choice forage every day. That means in the winter….hay feeding time at Paradigm Farms…. a horse weighing 1100lbs will eat roughly 22 pounds of dry hay every day…actually a bit more than that because we’re talking dry matter units, but work with me here.

Horses have an extremely wide genetic base and that leads to wide differences between horses experiencing the same conditions in terms of how much energy it takes to maintain their weight and general level of thrift no matter what external conditions do. And external conditions….particularly how cold it is and how wet it is…. have a huge impact on how much energy it takes to maintain a horse’s weight in the winter. Generally speaking, horses are most comfortable and thus maintain their weight most easily under dry, calm conditions between roughly 30 and roughly 65 degrees Fahrenheit. Add wind or rain or colder weather than the minimum and it can take vastly more energy to maintain weight and general homeostasis.

All that said, we know on this farm that the “average” 1100 lb horse will require roughly 28,000 kilocalories (calories) or 28 Mcal (megacalories) of energy per day in order to maintain homeostasis. You’ll note that the hay we tested has a Digestible Energy (DE) level of 2.14 Mcal/kg, or 0.97 Mcal/lb. That means each pound of hay contains 970 calories of energy. If, in our example, the average 1100 lb horse eats 22 lbs hay per day and we know the hay contains 970 calories per pound, we can calculate that this horse will get roughly 21000 calories from hay. That’s a deficit of 7000 calories per day…not enough to maintain weight, so we have to make up the difference with grain. Since there is a limit as to how much of anything a horse will consume before it’s sated I like to feed as energy dense a grain ration as it’s possible to build. Unfortunately for some reason most equine feed manufacturers do NOT place energy numbers on their tags or otherwise make them easily available so it’s something you will have to ask about at your feed store If you’re interested in how much energy your grain contains. The feed store may have that number on hand or they may have to phone the manufacturer to get it.

We know in this case that we have to make up a 7000 calorie per day deficit if we’re going to maintain weight on my hypothetical 1100 lb horse this winter. If the feed at hand contains 1500 calories per lb, we’ll need to feed 4.66 lbs per day to make up the difference. In this example that is a very do-able amount of grain to feed.

Unless the horse is a very easy keeper, energy will almost always be the most scarce or limiting macro nutrient in a horse diet and it’s almost always the most expensive macro nutrient to replace. For that reason, in my opinion, when we are buying a grain ration we need to worry a lot more than we do about how much energy each pound of feed contains.

Happy and Quigly