Feeding Oil to Horses: A Nuanced Look from a Nutrition Perspective
Recently, I’ve had several clients ask me about adding “cheap” oil—usually canola or generic vegetable oil—to their horse’s diet to help them gain weight. In many cases, they’ve been advised to do this by other horse people or even well‑meaning professionals. I also shared a post from @equineherbalist that contained some really useful insights about feeding oils. It got me thinking more deeply about the role oils play in equine nutrition—how they can be beneficial, but also where they may not be the best option.
With these recent client questions fresh in my mind, I felt it was the perfect time to take a closer look at oils, how they’re digested, and the healthiest ways to use them for condition and performance.
🧬 Why pouring on oil for weight gain isn’t always best
Many well‑meaning horse owners reach for the jug of cheap canola or vegetable oil to quickly bump up condition—but horses don’t handle large oil loads the same way ruminants or humans do.
Firstly, horses don’t have a gallbladder. Unlike humans and dogs, they constantly produce bile, which flows directly from the liver into the small intestine—there’s no storage pouch to release a big dose of bile all at once. This is because horses are trickle feeders—designed to graze and eat small amounts steadily throughout the day. When you suddenly introduce a large quantity of fat, the steady bile flow can’t keep up—leading to poor digestion, possible steatorrhea (excess fat in the manure), or digestive upset.
Secondly, fat is extremely calorie‑dense. Just 300 ml of oil provides roughly the same energy as 1 kg of oats. That makes it tempting for fast weight gain, but if you increase it too quickly or feed too much, you risk oxidative stress and micronutrient imbalances. Horses require extra vitamin E—around 100 IU for every 100 ml of oil fed—to counteract the increased free radical production that comes with higher fat intake.
Lastly, too much oil can upset the essential fatty acid balance. Many grain‑based diets are already high in omega‑6. Adding more omega‑6 from oils like sunflower or soybean can promote inflammation, whereas omega‑3‑rich oils like flax (linseed) can help reduce inflammation and support joint, coat, respiratory, and immune health.
The horse’s digestive anatomy in brief
Small stomach (~15 litres capacity) – begins to empty when it’s only about two‑thirds full, even if digestion isn’t complete.
Small intestine (~15 metres) – the main site for fat digestion and absorption, with bile flowing constantly from the liver.
Hindgut fermenter – fibre is broken down in the cecum and large colon by beneficial microbes; sudden dietary changes, including large amounts of oil, can upset this delicate microbial balance and increase the risk of colic.
These unique features mean oil should be introduced gradually, in moderation, and as part of a balanced feeding plan.
Which oils can be useful—and why
When choosing an oil, it’s not just the type that matters—the way it’s processed can significantly affect its nutritional quality. Cold‑pressed or expeller‑pressed oils are extracted without high heat or harsh chemical solvents, which helps preserve delicate fatty acids (especially omega‑3s) and natural antioxidants like vitamin E. In contrast, many cheaper oils are refined using high heat and chemicals, which can strip out beneficial compounds, damage the oil’s structure, and increase the risk of oxidation (rancidity) before it even reaches your feed room. Whenever possible, choose fresh, minimally processed oils stored in dark containers to protect them from light and heat damage.
Recommended oils:
Linseed (flaxseed) oil – High in omega‑3, with a healthy omega‑6:3 ratio and a good source of vitamin E. Great for supporting joint health, reducing inflammation, and improving coat shine—especially for horses with limited pasture access.
Canola oil – Balanced omega‑3:6 ratio, calorie‑dense, mild flavour, cost‑effective, and easy to source.
Rice‑bran oil (or micronised rice‑bran) – Provides slow‑release energy, essential fatty acids, and is often well‑tolerated by hard‑keepers.
Cod‑liver oil – Highly digestible, rich in vitamins A, D3, and E—but should be used sparingly due to its high vitamin content.
Oils to avoid in large amounts:
Sunflower or soybean oil—very high in omega‑6, which can promote inflammation in already grain‑heavy diets.
Any oil that has gone rancid—light and heat break down oils, reducing nutrients and producing harmful compounds.
How to incorporate oil safely
Assess the need – Only add oil if your horse requires more condition, needs extra slow‑release energy, or would benefit from coat improvement.
Start low and go slow – Begin with 30–50 ml/day, increasing by about 100 ml per week.
Know the limits – While research suggests that a healthy 500 kg horse can tolerate up to around 500 ml/day if introduced gradually, this is a theoretical maximum. In practice, most horses thrive on far less:
Coat & skin support: 50–120 ml/day (¼–½ cup)
Moderate calorie boost: 120–240 ml/day (½–1 cup)
High calorie needs: up to ~300 ml/day (around 1¼ cups) for hard keepers or high‑performance horses.
Feeding well above this can crowd out other nutrients, increase the risk of loose manure, and may not be well tolerated by every horse.
Balance with antioxidants – Supplement with vitamin E (around 100 IU per 100 ml oil) to support the body’s defence against oxidative stress.
Mix into the feed – Combine with a mash or soaked hay cubes to aid palatability and digestion.
Monitor your horse – Watch for changes in manure, coat condition, and energy levels, and adjust accordingly.
Alternatives to cups of cheap oil
If you’re looking to increase calories or improve condition without pouring in large amounts of oil, here are healthier, more sustainable options:
Maximise forage intake – Add alfalfa cubes, beet pulp, or soaked hay cubes for more calories while supporting hindgut health.
Micronised linseed or ground flax – Adds fat, fibre, and omega‑3 without overloading the digestive system.
High‑fat concentrates – Commercial feeds designed with balanced fats, vitamins, and minerals.
Energy‑dense forages – High‑quality hay or alfalfa for slow‑release energy.
In summary
Oil can be a valuable addition to your horse’s diet, but it’s not a one‑size‑fits‑all solution—and “more” is not always “better.” With no gallbladder and a digestive system built for constant, small meals, horses need oil introduced slowly, in moderation, and balanced with antioxidants.
When you choose high‑quality, minimally processed oils like linseed, canola, or rice‑bran and keep forage as the foundation of the diet, you’ll get the benefits of added calories and coat shine without compromising digestive health.
