Types of Calories – Are You Choosing Correctly?

Do you know how many calories your horse should be consuming in a day? Or if your hay has a high, or low-calorie content? Have you ever tried to modify behaviour with dietary changes? There is so much to think about when it comes to calories in the equine diet. Understanding the different types and the amount being provided is critical to optimizing nutritional management.

In North America, energy, in relation to nutrition, is measured in calories. A calorie is defined as the energy required to increase the temperature of 1 litre of water by 1 degree Celsius. In equine nutrition, Mcal is the most commonly used unit which is 1,000,000 calories.

Digestible energy (DE) is the total amount of the energy in the feed, less the amount of energy that the horse loses in the feces when that feed is digested. DE is commonly represented in Mcal/kg for feed and hay.

Calorie Types

Horses derive energy from three primary macronutrient groups, carbohydrates, fats and protein.

Carbohydrates

Carbohydrates are the primary source of energy in the equine diet and can be divided into three broad categories, structural carbohydrates, hydrolysable carbohydrates and rapidly fermentable carbohydrates.

Both rapidly fermentable and structural carbohydrates cannot be digested by digestive enzymes in the foregut of the horse. They must undergo fermentation in the hindgut. This process produces volatile fatty acids which are the most prominent energy source for horses.

Hydrolysable carbohydrates (HCs) can be broken down by digestive enzymes in the foregut of the horse. This leads to an immediate rise in blood glucose content and are therefore an immediate source of energy as they do not require fermentation. HC is the sum of ethanol soluble carbohydrates (ESC) and starch. Intake of HCs must be monitored very closely for horses with metabolic health issues.

Fats

Fats are the most calorically dense source of energy for horses. Despite not having a gallbladder, horses can digest and utilize fat, however, when adding fat, or increasing the amount, it should be done slowly to allow the horse to adapt.

The adaptation to increasing fat content in the diet includes an increase in lipase production (the enzyme responsible for breaking down fats) and elevated bile secretion. Bile in the horse is continuously secreted in small amounts. Additionally, the horse can develop improved absorption overtime as their body becomes more efficient in digesting and utilizing fat.

Proteins

The primary role of protein in the diet is to build and repair tissue, but it can also be used for energy when there are insufficient amounts of carbohydrates and fats. Protein is not a preferable energy source as the metabolic process is inefficient. This means that the horse must use energy to break down the protein. Therefore, protein is not efficient at fueling work for performance horses.

Modifying Calorie Intake

The first consideration when modifying calorie intake in a horse’s diet is whether you want them to gain, lose or maintain their body condition. Nutritional management of weight gain or loss comes down to calorie intake and output. So, if your horse needs to gain or lose weight, closely consider the number of calories in the diet and focus on adjusting that.

Another common question that clients tend to ask is if we can use diet to modify behaviour. Yes, it is possible to modify behaviour with diet, this relates to the type of calories being provided. Forage, often hay or pasture, is going to be the primary source of calories in the diet. So, you must first ensure that the program is balanced to meet the horse’s nutrient requirements. However, once we have the forage calculated, and the diet balanced, there can be opportunities to adjust the blend of supplemental calories being provided.

Hydrolysable carbohydrates like simple sugars and starches are absorbed quickly into the bloodstream and cause a rise in blood glucose. Relying heavily on HC for supplemental calories can make a horse more excitable. On the other hand, structural carbohydrates and fats are commonly referred to as ‘cool energy’ sources that do not contribute in the same way to excitability.

Putting It Together!

Let’s consider a case study. I worked with an off the track thoroughbred that regularly competed in hunters. He struggled to maintain weight, but his owner was also concerned with excitability resulting from additional calories.

His diet included free choice access to a lower energy forage, and supplemental concentrate that was primarily HCs. To increase weight, while working to reduce excitability, a higher calorie fibre source was added providing rapidly fermentable carbohydrates and a fat source was incorporated into his diet. This allowed us to increase the overall calorie intake for him, without the excitability that can be influenced by calorie type.

To conclude, optimal weight management and stamina starts with a base balanced diet that provides quality forage and meets the horse’s nutrient requirements. Choosing which type of calories to supplement depends on numerous factors. Are you trying to manipulate weight, behaviour, performance, a combination or all three? This will dictate which approach your nutritionist takes.

By: Madeline Boast, MSc. Equine Nutrition