How To Add Fat to a Horse’s Diet for Safe Weight Gain

By Dr Duncan Houston

Adding fat to a horse’s diet can be one of the most useful ways to increase calories without simply pouring more grain into the feed bin.

That matters because high-starch and high-sugar concentrate meals can increase the risk of digestive upset, colic, laminitis and equine gastric ulcer syndrome when overused. Fat gives you a more energy-dense option, especially for hard keepers, senior horses, horses in work, and horses that need calories while keeping starch lower. (MSD Veterinary Manual)

But fat is not a magic fix for every thin horse. If a horse is losing weight because of dental disease, parasites, ulcers, chronic pain, poor forage, kidney or liver disease, inflammatory bowel disease, or simply not getting enough hay, oil on top of dinner will not solve the real problem. The safest plan is to identify why the horse is thin, then add calories in a controlled, balanced way.

Quick Answer

Fat can help horses gain weight by adding concentrated calories without greatly increasing starch or sugar intake. Good options include high-fat commercial feeds, stabilized rice bran, flaxseed, and vegetable oils such as canola or flax oil. Introduce fat slowly over 2 to 4 weeks, monitor manure and appetite, and make sure the whole ration still provides enough forage, protein, minerals, vitamins and vitamin E. (University of Minnesota Extension)

Why Add Fat Instead of More Grain?

The main advantage of fat is calorie density.

Fat provides substantially more energy per unit than carbohydrates, and supplemental oil is highly digestible in horses. Mississippi State University Extension describes fat as a valuable energy source and notes that top-dressed oil supplements are highly digestible in horses, with digestibility reported around 88 to 98 percent. (extension.msstate.edu)

The clinical reason this matters is simple: some horses need more calories, but they do not need more large grain meals.

Large starch and sugar meals can overload the small intestine and disturb hindgut fermentation. MSD Veterinary Manual notes that feeding more than 50 percent of the ration dry matter as high-starch or high-sugar concentrate has been documented to increase the risk of laminitis, colic and equine gastric ulcer syndrome. It also recommends not feeding more than 0.5 percent of body weight in grain-based concentrate in a single meal. (MSD Veterinary Manual)

Fat can be useful when you want to:

• Increase calories without greatly increasing meal size

• Reduce reliance on high-starch grain

• Support hard keepers

• Help horses in moderate to heavy work

• Add calories for some ulcer-prone horses

• Support some low-starch diets under veterinary guidance

• Improve coat condition when the base diet is otherwise balanced

The important caveat: calories are still calories. A fat supplement can help a thin horse gain weight, but it can also make an easy keeper obese if used casually.

First, Ask Why the Horse Is Thin

Before adding fat, look for the reason your horse needs weight gain.

Common reasons include:

• Not enough total forage

• Poor quality hay

• Dental problems

• Parasites

• Gastric ulcers

• Chronic diarrhea

• Pain or lameness

• Poor access to feed in a group

• Increased workload

• Senior horse changes

• Poor absorption

• Chronic disease

• Inadequate protein, not just inadequate calories

University of Minnesota Extension recommends starting weight gain by maximizing forage, improving hay quality, and only then adding higher-calorie feeds or high-fat supplements when needed. It also notes that health problems are common causes of underweight horses and should be investigated with a veterinarian or nutritionist. (University of Minnesota Extension)

A thin horse with poor topline may not simply need fat. They may need better quality protein, amino acids, dental care, parasite control, ulcer treatment, pain management, or a full veterinary workup.

The practical checkpoint is this: if your horse is losing weight despite adequate feed, or needs increasing amounts of feed just to maintain condition, get a veterinary check before assuming the answer is more calories.

Which Horses May Benefit From Added Fat?

Fat can be helpful for:

Horse type	Why fat may help
Hard keepers	Adds calories without large grain meals
Horses in work	Supports higher energy needs
Senior horses	Can help if chewing and digestion are also addressed
Ulcer-prone horses	Helps add calories while keeping concentrates sparing
Some metabolic horses that are genuinely underweight	Adds calories without the same starch load, but needs careful planning
Horses needing low-starch diets	May help reduce reliance on cereal grains
Horses with some muscle disorders	May be part of specific veterinary nutrition plans

For horses with equine gastric ulcer syndrome, MSD Veterinary Manual recommends forage access, sparing use of concentrates, low to moderate NSC concentrate feeds when needed, and notes that vegetable oils can be used to increase dietary energy content. (MSD Veterinary Manual)

For horses with metabolic issues, nuance matters. Fat does not create the same glucose and insulin response as starch, but horses with equine metabolic syndrome are often overweight or insulin dysregulated, so adding calories may be the wrong move unless the horse is genuinely underweight. MSD notes that equine metabolic syndrome is linked to insulin dysregulation and that hyperinsulinemia leads to laminitis in horses and ponies. (MSD Veterinary Manual)

Which Horses Should Not Get Fat Casually?

Do not add fat casually to:

• Overweight horses

• Easy keepers

• Ponies prone to obesity

• Donkeys

• Horses with active laminitis

• Horses with uncontrolled equine metabolic syndrome

• Horses gaining weight too quickly

• Horses with unexplained weight loss

• Horses with diarrhea after dietary changes

• Horses with liver disease unless your vet has advised a plan

• Horses already on a high-fat commercial feed

Idle horses usually do not need added fat. University of Minnesota Extension states that fat can be beneficial for growing, hardworking, special needs and senior horses, but idle horses usually do not need it. (University of Minnesota Extension)

The biggest mistake is adding fat because it sounds “safer” than grain, while ignoring that the horse already has too many calories.

Best Fat Sources for Horses

1. High-fat commercial feeds

High-fat performance feeds or senior feeds can be a good option because they are usually balanced with protein, minerals and vitamins.

These are often easier than adding separate oil because the feed is formulated as a complete package. University of Minnesota Extension recommends considering a performance feed with 10 to 12 percent fat rather than simply increasing grain when a horse needs more calories. (University of Minnesota Extension)

Best for:

• Hard keepers

• Horses in work

• Horses already needing a concentrate

• Owners who want a balanced, less messy option

Watch-outs:

• Follow the feeding rate on the label

• Do not underfeed a fortified feed and assume the horse still gets the promised minerals

• Check NSC if the horse is insulin dysregulated or laminitis-prone

• Split concentrate meals into smaller feeds

2. Vegetable oil

Vegetable oil is the most concentrated fat source because it is essentially 100 percent fat.

Common options include:

• Canola oil

• Soybean oil

• Corn oil

• Flaxseed oil

• Blended vegetable oils

Oil is useful because it adds calories without adding much volume. The downside is that it provides calories but no protein, calcium, phosphorus, trace minerals or vitamins. It is an energy supplement, not a balanced feed.

A practical feeding range for many horses is gradually building toward 1 cup daily if needed, with some horses receiving up to 2 cups daily under appropriate guidance. Tennessee Extension notes that vegetable oil is commonly top-dressed at 1 to 2 cups per day for many horses, while MSD gives an approximate upper limit of 500 mL, or 2 cups, of soybean oil for a 500 kg horse. (UTIA)

Best for:

• Adding calories efficiently

• Horses that tolerate oil well

• Horses needing lower-starch calorie support

• Owners who can introduce it slowly and keep feed tubs clean

Watch-outs:

• Can reduce palatability in some horses

• Can make feed messy

• Can go rancid if stored poorly

• Does not balance the ration

• May cause greasy manure or diarrhea if introduced too fast

3. Stabilized rice bran

Stabilized rice bran is popular because it is palatable and less messy than oil. It contains fat, calories, some fiber and phosphorus.

The key word is stabilized. Unstabilized rice bran can spoil more quickly because of its fat content. Many commercial rice bran products are also calcium-fortified to help correct the naturally high phosphorus level.

MSD notes that rice bran is a high-fat product used for horses needing extra calories, but it is high in phosphorus and should be balanced for calcium. It also warns that rice bran is not a low-starch or low-sugar feed and should be avoided or used with extreme caution in insulin-dysregulated horses unless guided by a qualified equine nutritionist. (MSD Veterinary Manual)

Best for:

• Horses that dislike oil

• Hard keepers needing palatable calories

• Owners wanting a cleaner supplement than liquid oil

Watch-outs:

• Use stabilized products

• Check calcium balancing

• Do not assume it is safe for every laminitis-prone horse

• Follow label rates

• Avoid feeding large amounts without balancing the ration

4. Flaxseed

Flaxseed is useful because it provides fat, fiber, protein and omega-3 fatty acids.

It is less calorie-dense than straight oil, but it can be a good choice when you want a more whole-feed style supplement. Flaxseed oil is more concentrated than ground flaxseed, but it is more prone to oxidation and must be stored carefully.

Mississippi State University Extension lists flaxseed and flaxseed oil among omega-3-rich options and shows flaxseed oil has a much higher alpha-linolenic acid content than corn, soybean or canola oil. (extension.msstate.edu)

Best for:

• Horses needing omega-3 support

• Horses where coat and skin quality are part of the goal

• Owners who prefer a seed-based supplement rather than liquid oil

Watch-outs:

• Use ground or processed flaxseed, not whole seed that may pass through poorly digested

• Store carefully

• Introduce gradually

• Do not expect flax alone to fix major weight loss

5. Beet pulp, not fat, but still useful

Beet pulp is not a fat supplement, but it is worth mentioning because it is often a better calorie option than more grain.

It is a digestible fiber source that can add calories while keeping starch and sugar relatively low. MSD describes beet pulp as a source of calories and fiber, usually low in starch and sugar, and safer to feed daily in larger amounts than bran products. (MSD Veterinary Manual)

Best for:

• Horses needing more calories from fiber

• Horses with sensitive stomachs

• Horses where more hay is not enough

• Horses where grain intake needs to stay moderate

Watch-outs:

• Soak before feeding

• Check if molasses is added

• Balance minerals

• Introduce gradually

Which Oil Is Best?

There is no single best oil for every horse.

From a calorie perspective, most edible vegetable oils are similar. From a fatty acid perspective, they differ.

Oil type	Main point
Corn oil	Very high omega-6, low omega-3
Soybean oil	Higher omega-6, some omega-3
Canola oil	More balanced omega-6 to omega-3 profile
Flaxseed oil	High omega-3, but more expensive and more prone to oxidation
Fish oil	High omega-3, but often not palatable enough for weight gain amounts

Mississippi State University Extension shows corn oil has a much higher omega-6 to omega-3 ratio than canola or flaxseed oil, and notes that omega-3-rich sources include flaxseed, flaxseed oil, fish oil and canola oil. (extension.msstate.edu)

For weight gain, canola oil is often a sensible practical option because it is calorie-dense, usually palatable, and has a better omega balance than corn oil. Flaxseed oil may be useful when omega-3 intake is a priority, but it is not always the easiest or cheapest way to add large amounts of calories.

How Much Fat Should You Add?

Start low and build slowly.

A cautious plan for oil in a 500 kg horse might look like this:

Week	Example oil amount
Days 1 to 4	30 mL, about 1 oz, once daily
Days 5 to 8	30 mL twice daily
Days 9 to 14	60 mL twice daily if manure and appetite are normal
Weeks 3 to 4	Gradually increase toward the target amount if needed

Many horses do well around 120 to 240 mL daily, roughly 4 to 8 oz, when extra calories are needed. Some larger or harder-working horses may receive more, but high levels should be managed with a vet or nutritionist, especially if the horse has metabolic disease, diarrhea, liver disease, poor appetite or an already complex ration.

UMN recommends making feed changes gradually over about two weeks and notes horses take about three weeks to adapt to a high-fat diet. MSD notes that horses can tolerate about 10 percent fat in the total daily ration if introduced slowly and given 3 to 4 weeks to adapt. (University of Minnesota Extension)

For rice bran, follow the product label and check whether it is calcium-balanced. MSD notes rice bran is generally intended to be fed in limited amounts, often less than 1 kg per day. (MSD Veterinary Manual)

How Fast Should a Horse Gain Weight?

Weight gain should be gradual.

University of Minnesota Extension suggests feeding for a gain of about 0.5 to 0.75 pounds per day when the horse is otherwise stable and simply needs more calories. (University of Minnesota Extension)

In real life, I prefer owners to track progress over weeks, not days.

Use:

• Weekly weight tape measurements

• Body condition scoring every 2 to 4 weeks

• Photos from the side, front and behind

• Notes on appetite, manure and energy

• Saddle fit checks

• Topline assessment

Mississippi State University Extension notes that body condition cannot be changed dramatically in short periods and that energy increases should be gradual. If progress has not been made after a month, calorie intake may need reassessment. (extension.msstate.edu)

What Should You Monitor?

When adding fat, watch for:

• Reduced appetite

• Feed left behind

• Greasy manure

• Loose manure or diarrhea

• Weight gain that is too fast

• Increased body condition in the wrong places

• Dullness or poor performance

• Colic signs

• Laminitis signs in at-risk horses

• Feed tub residue or rancid smell

• Coat quality

• Muscle loss despite weight gain

Fat should improve the calorie balance, not create a new digestive problem.

If manure becomes loose, reduce the amount and slow the introduction. If the horse refuses the feed, switch strategy rather than forcing the issue.

Do High-Fat Diets Need Vitamin E?

Often, yes.

Vitamin E is an antioxidant, and high-fat diets can increase the need for antioxidant support. MSD Veterinary Manual states that horses consuming high-fat diets should also be supplemented with vitamin E to offset the increase in reactive oxygen species associated with fat metabolism. (MSD Veterinary Manual)

This is especially relevant for:

• Horses on little or no fresh pasture

• Horses on stored hay

• Horses in heavy work

• Horses receiving larger amounts of oil

• Horses with muscle disease

• Horses with poor coat or recovery issues

Do not guess large vitamin E doses blindly. A vet or equine nutritionist can help decide whether standard supplementation is enough or whether blood testing and higher therapeutic support are needed.

Special Case: Horses With EMS or Laminitis Risk

This is where owners can get into trouble.

Fat may be lower in starch than grain, but adding fat to an already overweight, insulin-dysregulated horse is usually the wrong direction. The priority for most EMS horses is controlled weight loss, low-NSC forage, exercise if sound, and reducing hyperinsulinemia risk. UMN notes that forages high in carbohydrates can be problematic for horses prone to laminitis and metabolic disease, and that sensitive horses are often managed with forage carbohydrate levels around 10 to 12 percent or less. (University of Minnesota Extension)

For an underweight insulin-dysregulated horse, the plan needs to be more careful. Possible options may include:

• Tested low-NSC hay

• Low-starch balancer

• Controlled beet pulp

• Carefully selected low-NSC senior or performance feed

• Small amounts of oil if needed

• Veterinary monitoring

• Insulin testing

• Regular hoof monitoring

Do not assume rice bran is automatically safe for EMS horses. MSD specifically warns that rice bran is not a low-starch or low-sugar feed and should be avoided or used with extreme caution in insulin-dysregulated horses. (MSD Veterinary Manual)

Special Case: Ulcer-Prone Horses

For ulcer-prone horses, fat can be useful because it helps increase energy without relying heavily on starch.

But the foundation is still forage.

MSD recommends ad lib forage access when possible, or at least avoiding more than 4 hours without forage, and using concentrates sparingly for horses with equine gastric ulcer syndrome. It also notes that vegetable oils can be used to increase dietary energy content. (MSD Veterinary Manual)

A good ulcer-conscious weight plan often includes:

• More forage time

• Suitable alfalfa or alfalfa mix where appropriate

• Smaller concentrate meals

• Low to moderate NSC feeds

• Added fat if extra calories are still needed

• Reduced long fasting periods

• Veterinary treatment if ulcers are suspected

Oil does not treat ulcers. It is a calorie tool that may help reduce the need for large grain meals.

Special Case: Senior Horses

Senior horses often lose weight because they cannot chew forage properly.

In that case, adding oil may help a little, but the bigger fix is usually dental care and forage replacement. University of Minnesota Extension notes that older horses may have worn or missing teeth and may need a complete feed when they can no longer chew hay effectively. (University of Minnesota Extension)

For senior horses, consider:

• Dental examination

• Complete senior feed if hay chewing is poor

• Soaked hay cubes or pellets

• Beet pulp

• Adequate protein and amino acids

• Fat as an add-on if needed

• Monitoring for PPID, pain, parasites and chronic disease

Do not use oil to cover up a senior horse that can no longer process their base forage.

Special Case: Topline Problems

Fat helps with body condition. It does not directly build muscle.

A horse with a poor topline may need:

• Better quality protein

• Essential amino acids, especially lysine

• Correct workload

• Pain assessment

• Saddle fit assessment

• Dental care

• Treatment for PPID or chronic disease where relevant

If you add fat and the horse gains a belly but the topline stays poor, you have added calories without solving the muscle problem.

What To Do Right Now

1. Body condition score the horse

Use your hands, not just your eyes.

Check fat over:

• Ribs

• Neck crest

• Withers

• Shoulder

• Behind the elbow

• Loin

• Tailhead

UMN notes that a body condition score between 4 and 6 is generally ideal, and that owners should feel the horse rather than only looking from a distance. (University of Minnesota Extension)

2. Check forage first

Before adding oil, ask:

• Is the horse getting enough hay?

• Is the hay good quality?

• Is the horse actually eating it?

• Is another horse pushing them away?

• Is there enough feeding space?

• Are teeth limiting chewing?

• Would better hay solve the problem?

Forage should remain the foundation. UMN recommends feeding mature horses at least 1 percent and ideally 1.5 to 2.5 percent of body weight in forage daily. (University of Minnesota Extension)

3. Choose one fat source

Do not add oil, rice bran, flaxseed and a new high-fat feed all at once.

Pick one change so you can see what the horse tolerates.

4. Start small

Start with a small amount and increase every few days.

If manure changes, appetite drops or the horse refuses feed, reduce the amount and slow down.

5. Balance the ration

Fat adds calories, but it does not automatically add protein, minerals or vitamins.

If you add oil to a forage-only diet, you may still need a ration balancer. MSD notes ration balancers are useful for horses on forage-only or low-concentrate diets to ensure proper nutrient intake. (MSD Veterinary Manual)

6. Recheck after 4 weeks

If there is no improvement after 4 to 6 weeks, reassess.

That may mean:

• Increase calories again

• Improve forage quality

• Check dental health

• Run fecal testing

• Screen for PPID

• Investigate ulcers

• Assess pain or chronic disease

• Work with an equine nutritionist

When Is This Urgent?

Adding fat is not usually urgent, but unexplained weight loss can be.

Call your vet promptly if your horse has:

• Sudden weight loss

• Weight loss despite good appetite

• Poor appetite

• Diarrhea

• Recurrent colic

• Fever

• Depression

• Difficulty chewing

• Quidding hay

• Dropping grain

• Bad breath or facial swelling

• Ventral edema

• Chronic cough or breathing effort

• Increased drinking and urination

• Laminitis signs

• A senior horse losing condition quickly

• A donkey, pony or miniature going off feed

Also call your vet if adding fat causes diarrhea, colic, complete feed refusal or marked behavioural change.

Common Mistakes Owners Make

Adding fat before checking teeth

A horse that cannot chew hay properly does not just need oil. They need dental assessment and often a different forage strategy.

Using fat to replace forage

Fat is not forage. Horses still need fiber moving through the gut.

Adding too much too quickly

This can cause feed refusal, greasy manure or diarrhea. UMN specifically notes that introducing a high-fat diet too quickly can cause greasy feces or diarrhea. (University of Minnesota Extension)

Forgetting vitamin E

High-fat diets may increase vitamin E needs, especially in horses on stored hay or in heavy work. (MSD Veterinary Manual)

Assuming rice bran is low-starch

It is not automatically suitable for insulin-dysregulated horses. (MSD Veterinary Manual)

Using rancid oil

Oils should be stored in a cool, dry place and protected from rancidity. Tennessee Extension recommends storing oils and high-fat feeds properly to prevent them from becoming rancid. (UTIA)

Expecting fat to build topline

Fat adds calories. Muscle needs protein, amino acids, correct work and a horse that is comfortable enough to use their body properly.

How To Prevent Weight Loss Coming Back

Long-term weight maintenance is usually about consistency.

Helpful steps include:

• Weigh tape weekly during weight gain

• Body condition score every 2 to 4 weeks

• Test hay when possible

• Keep forage intake consistent

• Make all feed changes gradually

• Maintain dental care

• Use fecal testing and parasite control

• Avoid large grain meals

• Split concentrates into multiple smaller meals

• Use a ration balancer when needed

• Match calories to workload

• Watch for seasonal weight loss early

• Reassess senior horses regularly

• Monitor metabolic horses carefully

UMN emphasizes gradual feed changes, routine dental care, body condition monitoring, fresh water, forage as the base of the diet, and feeding each horse as an individual. (University of Minnesota Extension)

Will My Horse Be Okay?

Most horses tolerate added fat well when it is introduced slowly and the rest of the ration is balanced.

The best outcomes happen when:

• The cause of thinness is understood

• Forage is adequate

• Dental problems are addressed

• Fat is introduced gradually

• Rice bran is calcium-balanced

• Vitamin E is considered

• Metabolic risk is respected

• Progress is tracked over weeks

• Calories are adjusted based on body condition

If the horse is simply a hard keeper, fat can be a very useful tool. If the horse is thin because of disease, pain, dental problems or poor absorption, fat may help temporarily but will not fix the underlying issue.

FAQs

Is oil safe for horses?

Oil can be safe for many horses when introduced slowly and fed as part of a balanced ration. It should not be poured in suddenly, and it is not appropriate for every overweight, laminitic or insulin-dysregulated horse.

Which oil is best for horse weight gain?

Canola oil is often a practical choice because it is calorie-dense, usually palatable and has a better omega-3 to omega-6 balance than corn oil. Flaxseed oil is richer in omega-3 but can be more expensive and more prone to oxidation. (extension.msstate.edu)

Is rice bran better than oil?

Not always. Rice bran is less messy and often very palatable, but it is not as calorie-dense as oil and must be calcium-balanced because of its phosphorus content. It is also not automatically suitable for insulin-dysregulated horses. (MSD Veterinary Manual)

How long does it take for fat to help a horse gain weight?

Expect changes over weeks, not days. Horses may take around 3 weeks to adapt to a high-fat diet, and visible body condition changes often need 4 to 8 weeks or more depending on the calorie deficit. (University of Minnesota Extension)

Can fat cause diarrhea in horses?

Yes, especially if introduced too quickly or fed in amounts the horse does not tolerate. Reduce the amount, slow the introduction and speak with your vet if diarrhea persists.

Final Thoughts

Fat can be an excellent tool for helping horses gain weight safely, especially when you need more calories without large grain meals.

But the best nutrition plan still starts with the basics: forage, water, teeth, parasite control, body condition, workload and overall health. Fat should support a balanced ration, not cover up an undiagnosed problem.

Use it thoughtfully. Start small, build slowly, choose the right source, balance the minerals and vitamins, and monitor the horse in front of you. A shiny coat is nice, but steady condition, normal manure, good appetite and safe metabolic control matter more.

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If you are unsure whether your horse needs fat, more forage, a senior feed, a low-starch plan, metabolic testing or a veterinary workup for weight loss, ASK A VET™ can help you work through the signs and decide what to do next.