This article has not yet been professionally approved. The information is based on the sources listed below.
Sweet itch in horses: feeding and its limits
What a ration check can clarify in sweet itch (summer eczema), how limited the feeding evidence is and why suspecting protein is no substitute for a diagnosis.
The short answer
Sweet itch is classified professionally as a hypersensitivity to the bites of certain insects. The consensus guideline puts reducing insect contact at the centre 1. A ration check can put nutrient intake into context, but it cannot make a skin diagnosis. Suspecting a protein-rich diet tells you neither the cause of the itching nor a suitable treatment.
Why should the skin question go to your vet first?
Itching can have various causes. Observing rubbing, damaged coat or skin changes is not enough to distinguish between these causes. If the trigger is unknown or symptoms persist, the professional information recommends a medical investigation 2.
- How long have you been observing these signs?
- Are season, location and insect contact documented?
- Which findings and measures have already been discussed?
- Which feed changes took place during the same period?
Where does feeding fit alongside insect protection?
The dermatological consensus guideline treats insect avoidance as the central measure. A change of diet does not automatically answer this question. Discuss the appropriate measures for your horse with your vet 1.
On the feeding side, you can document the complete ration: forage, pasture, concentrates and every other supplementary product. From this, nutrient intake can be checked against reference values. Such a balance is a feeding assessment, not a prediction of how the skin will develop 3.
What does the frequently cited linseed study show?
A blinded, placebo-controlled crossover pilot study included six horses over 42 days. It measured the response to a skin test with Culicoides extract. The smaller test reaction reported is a limited research finding; it does not demonstrate healing or a reliable improvement of natural symptoms in every horse 4.
So do not adopt either the trial preparation or a study dose as a self-treatment plan. Keep the question of a possible nutrient supplement separate from the question of diagnosis and veterinary care.
How do you assess the suspicion of too much protein?
Start with two different questions: how much protein does the horse take in, and what is causing the skin symptoms? The amino acid review describes differences in digestibility and the consequences of protein excess. It provides no evidence that an excess causes sweet itch or stomach problems 5.
Have total intake and usable protein checked on the basis of the ration. Do not remove protein-rich components solely because of the skin suspicion. A suspected feed allergy is, in turn, a separate veterinary question; the consensus guideline describes the evidence for it as limited and diagnostically difficult 1.
What belongs in a complete feeding log?
Take these documents to the professional consultation. The aim is traceable nutrient supply and a clarified skin question. An untargeted series of new products, on the other hand, makes it harder to describe what was changed and when.
- Note the amounts and analyses of hay, haylage and other forages.
- For your records, photograph the composition, analytical constituents and additives of every supplement 6.
- Enter every daily amount actually fed.
- Mark unknown pasture intake and missing values.
- Record changes with the date and keep observations separate from suspected causes.
Key takeaways
Frequently asked questions
Which feed reliably helps with sweet itch?
No generally effective feed can be derived from the evidence reviewed here. Professional assessment and limiting insect contact take priority; supplements must not be presented as a substitute for veterinary care 1.
Is too much protein the cause?
A suspicion based on the amount of feed is not a diagnosis. The cited guideline classifies sweet itch as an insect hypersensitivity. Protein excesses are a separate ration question and do not prove this link 15.
Can I just try linseed?
The pilot study in six horses examined the response to a skin test over 42 days. This does not lead to a general recommendation or a proven improvement in everyday stable life 4. Discuss possible ration changes with a professional.
Sources & studies
The content is based on the references listed below. It does not replace individual veterinary or feeding advice.
Show list of sources (6)
- Marsella R et al. (2023): Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology. Veterinary Dermatology 34(3):175–208Open-access consensus guideline (literature up to November 2022), DOI 10.1111/vde.13168: insect allergy, insect avoidance, diagnostic limits and weak evidence for feeding. Sweet itch is not equated with feed allergy or excess protein.
- Merck Veterinary Manual: Itching (Pruritus) in HorsesInformation for owners, checked on 29 September 2026: various causes of itching and veterinary investigation where the cause is unknown or symptoms persist. No diagnosis based on a feed list.
- Bayerische Landesanstalt für Landwirtschaft (LfL): Gruber Tabelle zur PferdefütterungPractical reference table with requirement and feed values based on the GfE recommendations; the basis of many ration calculations in German-speaking countries. Chapter 9.3, Table 39: most common poisonous plants for horses with habitat, toxicity and risk level (after Kamphues et al. 2014)
- O’Neill W, McKee S, Clarke AF (2002): Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Canadian Journal of Veterinary Research 66(4):272–277Abstract checked: six horses, 42 days, placebo-controlled blinded crossover pilot study; endpoint skin test reaction. No evidence of a cure or a generally reliable improvement in natural sweet itch (summer eczema) symptoms; no dosage recommendation derived.
- Mok CH, Urschel KL (2020): Amino acid requirements in horses (Invited Review). Asian-Australasian Journal of Animal Sciences 33(5):679–695Review of amino acid requirements: in horses essentially only lysine is quantitatively established; there are no robust requirement figures for methionine/threonine
- Verordnung (EG) Nr. 767/2009Placing on the market and use of feed, labelling and claims; definitions of complete feed (Art. 3(2)(i)) and complementary feed (point (j)), content of feed additives (Art. 8), feeding instructions (Annex II No. 4). Link to the current EUR-Lex consolidated version (as of 26 December 2018).