Feeding a horse with sweet itch focuses on reducing inflammation from the inside out, supporting skin barrier strength, and keeping body weight in check. Sweet itch is an allergic reaction to midge saliva that causes intense itching, and while no diet alone will cure it, the right nutritional approach can meaningfully reduce how severely your horse reacts each season.
Why Diet Matters for Sweet Itch
Sweet itch is driven by an overactive immune response. When a Culicoides midge bites, the horse’s immune system floods the area with inflammatory compounds, causing the swelling, itching, and skin damage that define the condition. What your horse eats influences how much inflammation the body produces overall, how quickly skin repairs itself, and whether excess body fat is amplifying the immune response. A targeted feeding plan won’t replace fly sheets or insect management, but it gives the body better tools to cope with each bite.
Omega-3 Fatty Acids: The Foundation
The single most impactful dietary change you can make is adding a rich source of omega-3 fatty acids. Research at the University of Guelph tested horses with Culicoides hypersensitivity and found that those fed flax meal daily for six weeks had a significant reduction in skin reactions compared to horses that received no supplement. The study used milled flaxseed at a rate of 1 pound per 1,000 pounds of body weight per day.
Flaxseed works because it’s packed with alpha-linolenic acid, an omega-3 fat the body converts into compounds that dial down inflammation. For a typical 500 kg horse, that translates to roughly a pound of milled flaxseed mixed into the daily feed. Whole flaxseeds pass through largely undigested, so always use milled (ground) or micronized flax. You can grind it fresh or buy stabilized pre-ground products. Fish oil is another omega-3 source some owners use, though flax is more palatable and widely available for horses. Expect to feed it consistently for at least four to six weeks before seeing results.
Keep Sugar and Starch Low
Horses that carry extra weight tend to have more severe sweet itch symptoms, and high-sugar diets are a major driver of both obesity and systemic inflammation. Excess body fat doesn’t just sit there. It actively releases inflammatory signaling molecules that disrupt insulin function and amplify the immune system’s overreactions, including allergic responses to insect bites.
Spring and summer pasture is often highest in water-soluble sugars, with concentrations reaching over 125 grams per kilogram of dry matter early in the grazing season. That’s exactly the time midges are most active, so your horse gets a double hit: peak allergen exposure plus peak dietary sugar. Practical steps include limiting grazing during sunny afternoons when grass sugar peaks, using a grazing muzzle, and choosing hay that has been soaked for 30 to 60 minutes to leach out sugars. Avoid cereal-based hard feeds, molassed chaffs, and treats high in starch. A forage-first diet built around soaked hay or low-sugar hay replacers keeps energy intake controlled without leaving your horse hungry.
MSM for Sulfur and Inflammation
Methylsulfonylmethane, commonly sold as MSM, is a sulfur-rich supplement widely used in horses for joint and skin support. A study in adult geldings found that 21 grams of MSM per day for 30 days reduced the expression of inflammatory genes after exercise. While that study looked at muscle rather than skin, the anti-inflammatory mechanism is the same, and MSM has a long track record among horse owners managing itchy skin conditions. It provides bioavailable sulfur, which the body needs to build keratin, the structural protein in skin, hair, and hooves. Most commercial equine MSM products recommend around 20 grams daily for an average-sized horse, and it mixes easily into feed.
Methionine and Biotin for Skin Repair
Horses with sweet itch often have damaged, thickened, or broken skin from constant rubbing. Two nutrients play a direct role in skin repair. Methionine is an essential amino acid (meaning the horse cannot make it and must get it from food) that supplies sulfur for the disulfide bonds that give keratin its toughness. Biotin signals the body to build new skin and hoof tissue. Together, they help the skin barrier recover faster between flare-ups.
Good dietary sources of methionine include soybean meal and linseed meal. If your horse’s diet is mostly forage, a balancer pellet formulated for the forage type (grass or alfalfa) will typically cover methionine and biotin needs. Standalone biotin supplements are also available, usually providing 15 to 25 mg per day for skin and hoof support. Results take time since new skin cells need to grow in, so plan on three to four months of consistent supplementation.
Nicotinamide (Vitamin B3)
One lesser-known option is nicotinamide, a form of vitamin B3. Patent research describes a trial in which five horses with sweet itch were given nicotinamide tablets mixed into their feed. After one month of treatment, the severity of their symptoms dropped substantially on a clinical scoring scale. The effective dose range was 0.5 to 2 mg per kilogram of body weight per day, which for a 500 kg horse works out to roughly 250 mg to 1,000 mg daily. Nicotinamide supports skin barrier function and has known anti-inflammatory properties in other species. It’s available as a standalone supplement, though it’s not yet a mainstream equine product, so sourcing may take some effort.
Brewers Yeast: Worth Trying?
Brewers yeast is a traditional recommendation for sweet itch, with the claim that it makes the horse’s blood taste bitter and discourages midges from biting. There’s no strong scientific evidence behind the repellent claim, but brewers yeast is a natural source of B vitamins and amino acids that support general health. It’s unlikely to do any harm and may offer modest nutritional benefits, particularly for horses on limited diets. Treat it as a low-cost addition rather than a primary strategy.
Putting It All Together
A practical daily feeding plan for a horse with sweet itch might look like this:
- Base diet: Low-sugar forage, either soaked hay or tested hay with non-structural carbohydrates below 10 to 12 percent. Limit or time-restrict pasture access, especially on sunny days.
- Omega-3 source: Roughly 1 pound of milled flaxseed per 1,000 pounds of body weight, split between meals.
- Balancer pellet: A ration balancer matched to your forage type, covering vitamins, minerals, methionine, and biotin without adding excess calories.
- MSM: Around 20 grams daily, mixed into feed.
- Optional additions: Nicotinamide at 0.5 to 2 mg/kg body weight, brewers yeast as a B-vitamin top-up.
The overarching goal is to keep your horse at a healthy weight, flood the diet with anti-inflammatory fats, and provide the building blocks for strong skin. Start supplements well before midge season if possible, since most take four to six weeks to show effects. None of these changes replace physical barriers like fly rugs or stable management during dawn and dusk when midges are most active, but a well-designed diet gives your horse a measurably better chance of getting through summer comfortably.