Understanding Horse Nutrition, Part 2: Calories, Kilocalories, Megacolories--How Much does your Horse Need?

 Written By Dr. Kris Hiney
Energy means calories!Last month we discussed your ability to evaluate your horse’s body condition, and what the optimal condition for your individual horse may be. This month we delve a little further into the energy requirements for horses. Remember – when referring to energy, we mean calories! As stated last month, it does not mean how your horse feels. There are many other factors that influence your overall horse’s attitude, and while certainly how many calories he consumes is part of it, it isn’t the entire picture.
Let’s talk technical.

In the equine world, due to the horse’s body size, we talk about their energy requirements in megacalories (Mcal). One Mcal is equivalent to 1000 kilocalories (kcals). To make it relatable, the average woman between 31 and 50 years of age who is moderately active is recommended to consume 2000 kcal/d. That would be equivalent to 2 Mcal for a horse.

How much energy (or calories) does your average horse need to consume per day?Well, first we need to define even what average is. When we discuss energy requirements, we usually begin with the animal’s maintenance requirements. Maintenance is defined as a mature horse not undergoing any exercise program or reproducing. Essentially the average, older horses just out hanging around. Numerous researchers have studied the energy requirements of horses, and as a result we have equations to calculate exactly how much a horse needs to eat. For example, the maintenance requirement of an average 1,050 lb horse would be 14.5 Mcal/d. These numbers are derived from the body weight of the horse multiplied by the energy required to maintain one kilogram of that horse’s body weight.But even average is not always average. The defined maintenance requirements for horses are based on horses in a moderate condition – those horses between 5 and 5 ½ we talked about last month. If your horse is overly fat, he needs less energy to keep him at the same weight. Fat tissue is metabolically less active than lean tissue, or muscle. Therefore, a 1,100 lb horse who is fat actually needs to eat less than a 1,100 lb fit horse to maintain the same weight.
Where do these numbers come from?

For those truly interested, the results of equine nutrition studies have been combined into a lengthy document entitled The Nutrient Requirements of Horses edited by the National Research Council (NRC). Teams of scientists world-wide review the collected work of all researchers to create recommendations published in this document. Animal nutritionists use “NRCs” to determine the nutrient requirements of all species of livestock and companion animals. The latest NRC for the horse was published in 2007 and is available through the National Academies Press (www.nap.edu). If you would like to calculate your own horses requirements from scratch, this book will provide the equations to do so.

Understand the important goal. Now, the point of this discussion is not to have you whip out your calculators and revisit your algebra and calculus days. The important goal is to understand what factors we have control over that will alter how much energy our horse needs. Then we will discuss how best to meet these energy requirements to optimize your horse’s health and performance.
Easy keeper or not?Even your horse’s overall temperament will change its energy requirements. We have long known that hotter, or more nervous horses take a lot more feed to keep weight on, while those with a more laid back attitude need less feed. Typically those horses that were selected to have a more laid back personality, such as our stock breeds or draft horses, fall into that easy keeper category vs our horses who were selected for speed (think Thoroughbreds).On average, a more active horse (youngsters in pastures, nervous Thoroughbreds) will need 20% more energy than an inactive horse to maintain its weight. So let’s say we have a 1,100 lb laid back, fatty American Quarter Horse vs an active, lean 1,100 lb Thoroughbred mare. Our laid back horse needs 14.8 Mcal/d while our active girl requires 17.8 Mcal/d (see Table 1 to estimate your horse’s maintenance requirement). She will need to eat 3 Mcal/d more than our couch potato. That’s even before we start working her!
Table 1. Energy requirements for maintenance (Mcal/d) based on average activity level.

Wt of horse (lb) Couch potato Average Active
900 12.2 13.4 14.6
1000 13.5 14.9 16.2
1100 14.9 16.4 17.8
1200 16.2 17.8 19.4
1300 17.6 19.3 21.1

The second major variable in the maintenance requirement for a horse is the weather. The calculated maintenance requirements are based on an environment that requires no energy by the horse to keep themselves warm. We call this the thermoneutral zone. Horses do quite well in cold temperatures if they have become accustomed to them. Cold adapted horses do well in temperatures as low as 5º Fahrenheit (F). However, horses will have trouble keeping warm if the weather suddenly changes and if the horse hasn’t grown the proper hair coat. But all horses, even fuzzy Wisconsin ones, will have trouble if they do not have protection from the wind or from rain, especially sleet. This chills a horse rapidly when the fluffy, protective insulation of their hair coat is slicked down to their body.

How much energy does a horse need to stay warm? Below 5 º F, a horse needs to use energy to keep warm, and that temperature is referred to as the lower critical temperature. (Which is nothing for those of us living up here in the Northern Midwest – brrrr). So how much energy do they need to stay warm? On average, for every drop in temperature of 14 º F below the lower critical temperature, they will need 20% more energy. Let’s say the temperature drops to -10 F º and we are feeding our energetic girl. She will now need 21.4 Mcal/d for maintenance, an increase of 3.6 Mcal/d over her normal maintenance requirements.
Gaining weight for insulation.

There are additional strategies we can take to prepare our horses for winter weather, other than providing adequate shelter and letting them grow a hair coat. Adipose tissue, or fat, helps insulate horses against the chill of the winter weather, just like in polar bears. Now let’s say our higher strung mare is also thin, about a condition score 4. Well, clearly we would like to put some weight on her, especially before Old Man Winter arrives. To change body condition scores in horses by 1 value (ie a 4 to a 5), we have to really start feeding them, especially if you want to put that weight on more rapidly. If our goal is to put weight on the mare in as little as 60 days, we would have to increase her caloric intake by 5.3 Mcal/d, or 30% of what she was consuming. If our goal is a little more gradual, let’s say over 4 months, her diet would be increased by 2.7 Mcal/d or 16% of her current intake.

Not sure how much your horse weights?

Weight tapes are available at most feed stores at a fairly nominal price ($2-3). But for even more fun (great for kids and 4-H activities) you can do it yourself with a string and a measuring tape. Use one string to measure the distance around your horse’s heartgirth (HG). Make sure your horse is standing square and your string is around your horse perpendicular to the ground. Then measure the length of your horse’s body (BL) from the point of his shoulder to his buttock, just like you were measuring for blanket fit. Again, be sure your horse is square and that your string is held level to the ground. Measure your two strings in inches using your tape measure. Then use this simple formula
Wt of your horse (lbs)= (HG)2 x BL
330 Wallah! Now you know how much your horse weighs!
Quick tip.While we haven’t discussed energy sources (coming soon), a great way to put weight on horses is to add fat to the diet. Fat has 2.25 x the amount of calories per lb compared to anything else we can feed our horses. Need to put weight on before winter? Check out some fat added feeds, or add safe fat sources made with stabilized ground flax seed and/or stabilized rice bran -- Omega Horseshine®, Omega Antioxidant, Omega Grande®, Omega Stabilized Rice Bran, or those famous Horse Journal™ recommended horse treats Omega Nibblers®. These supplements add calories quickly and safely and are better than just increasing how much your horse is eating.

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