This is an abbreviation of unit 4 from the Advanced Equine Nutrition course. The complete text, a video, and quiz questions are available with The Horse’s Advocate membership. You can also purchase them separately. Note: Passing the Basic Equine Nutrition Course is required before starting the Advanced Course.

Unit 4 – Food: Energy Intake for Horses

Understanding the concept of energy flux, which I covered in Unit 3, is where our journey into equine nutrition began. It’s the First Law of Thermodynamics, a fundamental principle that needs to be at the forefront of our discussion. This law states that “what goes in must come out.” The horse absorbs the energy stored in food. Various factors influence that energy. This results in its use, storage for future use, or elimination. This knowledge empowers us to make informed decisions about our horse’s diet. 

This unit explores the first step of energy flux: food intake and the energy it supplies. So, let’s delve into the science and start our journey toward equine nutrition mastery.

The Math Of Energy

Energy is the ability to do work. The unit of energy stored in food is called a kilocalorie (kcal). One kcal is based on the metric system. It refers to the energy needed to heat 1 kilogram (kg) of water by one degree of temperature. This process happens between zero and 1 degree Celsius. It matters that the letter “c” in calories is small because there are 1000 (small-c) calories in 1 kcal. In America, it has become popular to call 1000 (small-c) calories (or 1 kcal) a capital letter, “C” Calorie.

1 (large-C) Calorie = 1 kilocalorie = 1000 calories

Scientists now measure energy as joules, used in many parts of the world, replacing Calories, calories, and kilocalories. A joule measures the work done when the force of one Newton moves an object. This movement covers a distance of one meter in one direction. If your country does this, you must convert what is written here by these factors:

1 calorie = 4.184 joules

1 Calorie or 1 kcal = 4.2 Kilojoules

Of all the nutrients placed into the mouth of the horse, only protein, fat, and sugar can directly convert their stored energy. This energy converts into measurable energy released or used. The amount of energy released by each is standard:

• 1 gram of protein releases 4 calories or 16.74 joules
• 1 gram of carbohydrate releases 4 calories or 16.74 joules
• 1 gram of fat releases 9 calories or 37.66 joules

Key Points:

1. Energy is measured in calories, Calories, kilocalories, and joules. 1 Calorie = 1000 calories = 1 kcal. 1 calorie =4.184 joules and 1 Calorie =4.184 kilojoules.
2. 1 g protein or 1 g carbohydrate each contains 4 calories = 16.74 joules, but 1 g fat contains 9 calories =37.66 joules.
3. The basal metabolic rate (BMR) is a horse’s minimum energy requirement to remain alive. It also includes what horses do when there is no added stress. Hundreds of factors affect the BMR, and feeding must account for these changes.
4. Scientific studies offer caloric ranges for a set or group of horses. However, these ranges may not hold for individual variations in energy required.
5. Accurate data to establish changes in horses’ body condition requires equipment most horse owners need access to.
6. Develop an eye for determining the body condition score (BCS) and learn to assess the top line score (TLS). It takes practice to become effective.
7. Looking for changes over time will determine if the BCS and the TLS are moving in the intended direction.
8. The overall attitude and demeanor is the best, but often overlooked, evaluation of a horse’s condition. Step back and honestly evaluate this.
9. Keep a dated journal. Include any data collected, such as girth measurements and pictures. Record muscle loss, such as hay belly. Note hair and hoof quality, allergies, and behavior.
10. Focus on what you can control (food intake, stress, work). Adjust the dials as necessary. Always step back and take in the whole, individual horse.