Adding fats and oils to your horse’s diet is a great way to increase calorie supply without relying on grains and high-NSC feeds.
Fats can be added to the diets of underweight horses as weight gain supplements. Oils also provide cool energy to support exercise performance, weight maintenance and gut health.
High-fat feeds are typically made with rice bran, ground flax, or vegetable fat. Oils such as canola, soybean, flax, or camelina oil are also popular options for horses.
All oils and pure fats provide the same amount of caloric energy per gram. However, not all oils are equal in terms of how they influence processes in the body.
When deciding which fat supplement to add to your horse’s diet, equine nutritionists also care about the fatty acid composition of the feed. As this article will discuss, certain fat sources have advantages over others.
Fat in the Equine Diet
Wild horses evolved to graze for up to 16 hours per day on fibrous forages on vast low-quality grasslands.
On a forage-only diet, most of the horse’s energy needs are met through hindgut fermentation of fibre, with only small amounts of fat present in the diet.
Hay and pasture typically contain 1 – 3% fat on a dry matter basis. This means that an average-sized horse consuming 10 kg (22 lb) of forage only gets 100 – 300 grams of fat in their diet per day, and not all of this will be absorbed in the gut.
Although not a significant part of the horse’s natural diet, there are some considerable advantages to supplementing your horse with fats in modern management settings.
Grains vs. Fats
Commercial feeds for horses with high calorie needs often contain grains or grain by-products as energy sources. Examples of grain-based ingredients include:
- Ground corn
- Ground wheat
- Corn germ meal
Although grains add calories to the diet, they are also high in non-structural carbohydrates (NSC) such as starch and sugar.
Horses have small stomachs and are not well-suited to digest large grain-based meals. Undigested starches and sugars spill over into the hindgut and cause gut health issues, such as dysbiosis, gastric ulcers and hindgut acidosis.
Oils and fats are often a better option than grain-based feeds to increase the calorie density of the diet because they provide calories without starch and sugar.
Replacing grain with fat sources can help to protect the health of your horse, reducing the risk of digestive issues or metabolic dysfunction.
Benefits of Feeding Fat
There are several additional benefits to meeting the energy requirements of performance horses from fat instead of carbohydrates. These benefits include:
- Reduce heat from digestion: The digestion of fats generates less heat than protein and carbohydrate digestion. Fats are a great option to provide cool calories for performance horses or for horses in hot climates.
- Spare glycogen: Glycogen is the preferred energy source for contracting muscle. However, horses performing low-intensity exercise can adapt to using more fat for energy. Horses in high-intensity exercise may still require some starch and sugars in the diet to restore glycogen stores post-exercise. 
- Improve performance: In some studies, horses adapted to added fat had faster race times, delayed fatigue, and reduced heart and respiratory rate. This could be due to reduced dry matter intake and therefore less gut fill, glycogen-sparing and reduced metabolic heat. 
- Decrease tying-up: High-starch diets contribute to high frequency of tying-up episodes. Decreasing starch and using fat for energy can help reduce the risk of recurrent exertional rhabdomyolysis. 
- Promote calm demeanour: Research suggests that replacing starch with fat reduces startled behaviour and reactivity to new noises and visual stimuli in horses. 
The fats found in your horse’s forage, feed and supplements are mostly in the form of triglycerides. These are molecules that consist of three chains of fatty acids bound to a glycerol backbone.
Fat digestion occurs in the small intestine, which is the area of the horse’s gastrointestinal tract that food passes through after it leaves the stomach.
In the small intestine, digestive enzymes and bile acids break down triglycerides into fatty acids and glycerol. These components are absorbed by the intestine and re-made into triglycerides to be delivered throughout the body.
Most mammals have a gall bladder which stores bile acids and releases them into the small intestine when a meal is consumed.
Horses do not have a gall bladder. Instead, they synthesize bile acids in the liver and continuously secrete bile into the small intestine.
Fat is a particularly efficient energy source for the horse because its digestion does not produce a lot of heat.  In contrast, fibre fermentation in the hindgut results in significant energy loss to heat production.
Research shows that horses on a high-fat diet had a 14% decrease in body heat production, meaning that more energy was available to fuel athletic performance and other metabolic functions. 
Although horses have evolved to subsist on low-fat, high-fibre diets, they can adapt to a high fat intake.
Studies show a linear relationship between the amount of fat in the diet and the amount absorbed. This means that as the fat content of the diet increases, the horse is able to absorb more fat up to intakes of over 2 kg per day. 
Fats in forages and grains are less digestible than those in added fats, such as oils or high-fat concentrates. This means that more of the fat is available for the horse to use as energy when provided in the form of fat supplements.
Fat molecules in forages and grains are found within the plant cell, which is surrounded by a rigid cell wall. This structure makes it harder for enzymes to access the fat and break it down into fatty acids for absorption.
How to Feed Fat to Horses
Because fats do not make up a significant portion of the horse’s natural diet, horses need to be slowly adapted to added fat sources.
Oils can be top-dressed on the current diet, mixed in with forage cubes/pellets or even poured directly onto your horse’s hay. Start with feeding 30 ml (1 oz) of oil daily and increase as needed by half an ounce (15 mL) every three to four days.
If you are starting your horse on a high-fat feed, introduce 25% of the desired feeding rate for three to four days and increase gradually after that.
This gives your horse’s body time to increase the production of digestive enzymes and adjust to handle higher fat intake.
Note that if you are giving your horse a high-fat commercial feed below its recommended feeding rate, you will be undersupplying vitamins and minerals. Horses on a high-fat diet should have adequate levels of all micronutrients, but especially antioxidant vitamins and minerals.
Monitoring for Changes
Introducing fat supplements to your horse’s diet too quickly can cause gut problems. If fats are not fully absorbed in the small intestine, they can reach the hindgut, altering gut microbial populations and impacting fibre digestion.
Monitor your horse’s feces for changes that suggest the fat was introduced too quickly: 
- Sheen on well-formed fecal balls
- Greasy or grayish appearance
- More abundant feces
- Loose feces
If you notice these signs, reduce the amount of oil or fat temporarily until your horse’s bowel movements return to normal. The fat sources can then be re-introduced at a slower rate.
How Much Fat to Feed your Horse
The amount of fat to add to your horse’s diet depends on their calorie needs and the digestible energy content of the rest of their diet.
All oils provide roughly 9 kilocalories (kcal) of energy per gram (mL) of oil. In comparison, carbohydrates and protein provide 4 kcal per gram, making fats a much more concentrated energy source.
If you were to feed your horse 30 mL (1 oz) of oil, this would provide 270 kcal of energy.
Most horses should be fed a diet with less than 8% total fat content. However, heavily-exercised horses can be fed up to 20% or more of their digestible energy requirement from fat. 
Energy Requirements for Horses
Energy requirements for mature horses are calculated from body weight and exercise level. The amount of adipose tissue (fat) they have stored also influences how many calories should be fed.
A typical mature horse at maintenance requires 16.6 mcal (16,600 kcal) per day whereas a horse in heavy exercise requires 26.64 mcal (26,640 kcal) per day. 
If your horse is overweight, some energy needs can be provided by stored body fat and they do not need as many calories added to the diet.
Underweight horses need all of their calories to be provided by the diet and require additional calories to support weight gain.
It’s important to accurately assess your horse’s body condition to determine how much fat to feed. Our nutritionists can help you body condition score your horse if you upload a photo online.
Energy Content of the Diet
To calculate how much fat to feed, you will also need to determine how much caloric energy is supplied by your horse’s overall diet.
Most horses should get the majority of their energy from forages. Legume hays and immature forages typically provide more digestible energy than grass hays or mature forages.
You can find out how much digestible energy is supplied by your horse’s hay with a forage analysis.
Submit your horse’s feeding program to our online diet balancing tool to get an estimate of the energy content of your horse’s diet. Our nutritionists can also help you determine how much fat to add to your horse’s diet.
Best Fat Supplements to Feed
There are several options for adding fat to the equine diet, including high-fat concentrates and liquid oils.
Some examples of high-fat feed ingredients include:
- Vegetable fat
- Rice bran
- Dried distiller’s grains
- Ground flax
Suitable oils for adding calories to equine diets include:
The main difference between these fat sources is their fatty acid profile. Below, we will discuss the advantages and disadvantages for different fat additives.
Oils contain many types of fatty acids, including saturated, monounsaturated, polyunsaturated, and trans fats. Generally, unsaturated fatty acids are associated with better health outcomes than saturated and trans fats.
Polyunsaturated fatty acids (PUFAs) in particular have been studied for their health benefits in humans and animals. PUFAs can be further classified into three categories:
- Omega-3 fatty acids
- Omega-6 fatty acids
- Omega-9 fatty acids
Omega-3 fatty acids are anti-inflammatory while omega-6 fatty acids are generally pro-inflammatory. Because both anti-inflammatory and pro-inflammatory processes are important for the horse’s health, both of these fatty acids are required in the equine diet in the appropriate balance.
Omega-3 to Omega-6 Ratio
Dietary recommendations often focus on providing an “optimal ratio” of omega-3 to omega-6 fatty acids in the diet. However, an optimal ratio has not been established for horses.
However, it is generally true that horses consuming forage-based diets tend to have a healthy ratio of omega-3 to omega-6 fats in the diet. Horses on a grain-based diet tend to have an over-abundance of omega-6 fats and not enough omega-3s.
Omega-3 Fat Supplements
Plant-based oils such as flax, canola and camelina oil are commonly fed to horses as a source of omega-3 fatty acids.
However, these plant sources do not contain the long-chain fatty acids that are directly involved in anti-inflammatory processes.
The major omega-3 found in forages and plant oils is alpha-linolenic acid (ALA).
ALA must get converted into the long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) to have anti-inflammatory effects.
This requires a series of enzymatic reactions that elongate and desaturate the ALA molecule into DHA and EPA. But mammals are only able to convert a small fraction of ALA to DHA and EPA, estimated between 4-10%. 
Supplementing horses with ALA from flax oil does not increase DHA or EPA levels within cells.  This means that supplementing your horse’s diet with ALA will not yield an anti-inflammatory benefit.
Benefits of DHA and EPA for Horses
If you want to supplement your horse’s diet with omega-3 fatty acids for anti-inflammatory benefits, it is better to provide DHA and/or EPA directly from marine sources such as fish oil and microalgae.
In the following section, we will discuss some of the benefits associated with feeding DHA and EPA to horses.
Cell Membrane Fluidity
Fatty acids are important components of cell membranes. The fatty acids provided by your horse’s diet are incorporated into the structure of cell membranes and affect their function.
Omega-3s like DHA and EPA make the cell membrane more fluid, alter signaling processes and modulate responses to hormones.  Immune cells, joint chondrocytes and muscle cells with a higher proportion of DHA and EPA respond differently to stress.
Research shows that DHA and EPA help to reduce inflammation and support joint comfort in horses with arthritis.
In healthy horses, feeding marine-derived oils resulted in a lower level of pro-inflammatory molecules compared to feeding flax oil. Horses fed DHA and EPA might also be protected against cartilage breakdown when inflammation occurs in the joints. 
In one equine study, feeding DHA reduced inflammation and the presence of immune cells in joint fluid. After 90 days of supplementation, the horses placed more weight on their arthritic limbs suggesting improved comfort. 
Another study found improved trot stride length in horses supplemented with fish oil. 
Although lab tests using isolated cells have suggested joint health benefits from plant oils, feeding these to horses doesn’t lower pro-inflammatory molecules.  Therefore, it is unlikely that these oils will benefit joint health in horses.
Pathological inflammation occurs in horses with respiratory allergies, heaves, and asthma. Horses with these conditions can experience excessive coughing, poor performance and management difficulties.
Several studies have assessed omega-3 supplementation in horses with recurrent airway obstruction (heaves).
Supplementing DHA decreased the number of immune cells in lung fluid and improved cough scores in horses with RAO. Inflammatory markers were also reduced suggesting improvement in the immune response to triggers of respiratory illness. 
Oils and fats support skin health by enabling sebum production. Sebum is a waxy substance that makes the coat gleam and provides a protective barrier against irritants.
Omega-3 fatty acids not only promote sebum production but also mitigate allergic reactions to reduce itching and swelling in the skin. 
Horses with equine metabolic syndrome (EMS) are less sensitive to the effects of the hormone insulin, which makes it harder for them to handle sugars in the diet.
Metabolic horses also commonly experience whole-body inflammation, which perpetuates insulin resistance. Improving insulin sensitivity can help EMS horses maintain a healthy body condition and reduce the risk of complications, such as laminitis.
Feeding fats in place of grains to meet calorie needs is a good way to decrease sugar levels in the blood. Additional benefits have been observed with metabolic horses fed omega-3 fatty acids.
In one study, horses with insulin resistance that were fed marine-sourced fatty acids or flax had improved glucose handling and insulin responses. 
In another study, DHA reduced inflammation in horses with equine metabolic syndrome.  This may further help to improve insulin sensitivity.
Other benefits of omega-3 fatty acids have been observed in horses including:
- Reduced stress response: Mares given DHA and EPA had decreased cortisol levels following trailering stress and stall confinement. 
- Improved reproductive health: DHA supplementation improves sperm quality in stallions and supports faster uterine involution in mares following delivery. 
- Improved cognitive function: Foals born to mares supplemented with DHA during pregnancy had better learning abilities and memory at 1 and 2 years of age. 
Fats are a great way to add calories to your horse’s diet. Choosing a fat source with anti-inflammatory omega-3 fatty acids can provide additional benefits.
Look for fat supplements that contain DHA and/or EPA, which can only be obtained from marine sources, such as fish oil and microalgae.
DHA derived from microalgae tends to be more palatable for horses than fish oil.
Feeding your horse DHA can help support joint mobility, exercise performance and recovery, respiratory health, reproductive function, cognitive function and healthy stress responses.
Mad Barn’s w-3 Oil is a fat supplement enriched with DHA from microalgae as well as high levels of natural Vitamin E.
Feeding w-3 Oil can support healthy regulation of inflammatory processes in the horse’s body while supplying cool energy for horses with higher calorie needs.
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