Sainfoin for Horses: Benefits, Nutrition, Parasites, and the Important Ivermectin Interaction

Sainfoin (Onobrychis viciifolia) is a perennial forage legume that’s gaining attention in equine feeding conversations for a reason: it combines the nutrient density and palatability people expect from a quality legume with a distinctive plant chemistry—condensed tannins—that can influence digestion, parasite biology, and even how certain dewormers behave in the body.

If you’re researching “sainfoin for horses,” the practical question is usually one of these: Is it a good hay or pellet to add to my program? Can it help with parasites? And is it safe alongside routine deworming? The evidence-supported answer is: sainfoin can be a useful, palatable forage with some measurable anti-parasite pressure in specific contexts, but it is not a stand-alone deworming strategy—and it may interact with orally administered ivermectin in clinically meaningful ways.

This article synthesizes key findings from published research and reference databases, focusing on what horse owners and barn managers can actually do with the information.

What Is Sainfoin and Why Horse Owners Are Interested

Sainfoin is a forage legume historically used in livestock systems. For horses, its appeal typically centers on three points:

First, it’s nutrient-dense and generally well-accepted. Second, it contains condensed tannins (also called proanthocyanidins), which can bind proteins and influence gut biology. Third, those same tannins have been studied for potential effects on equine internal parasites—particularly small strongyles—though results vary depending on the form and amount fed.

Unlike some other legumes, sainfoin is associated with “antibloat” characteristics in ruminants because tannins can reduce frothy bloat risk. That ruminant-specific issue isn’t a primary concern in horses, but it highlights that sainfoin’s tannins are biologically active—useful to understand before you feed it at meaningful levels.

Nutritional Profile: How Sainfoin Compares to Other Forages

From a straightforward feeding standpoint, sainfoin is often discussed as a legume alternative or complement to alfalfa, especially when owners want a palatable, higher-protein forage that still fits within a carefully managed ration.

According to analyses compiled by Feedipedia, typical sainfoin crude protein in fresh forage is around 13–21% of dry matter, with neutral detergent fiber (NDF) commonly in the mid-30% to mid-40% range; reported metabolizable energy is broadly similar to good-quality legume hays. These values help explain why producers view it as a viable nutrient-dense forage for horses that need more than maintenance-level grass hay can provide—especially when fed at an appropriate maturity stage and supported by an actual forage analysis from your supplier. Source: https://www.feedipedia.org/node/703?utm_source=equiniction

What does this mean in a barn context?

If you have a horse that struggles to hold weight on average grass hay, or one that benefits from a more protein-forward forage base, sainfoin hay or pellets may function similarly to other legumes: it can raise the nutrient density of the diet without automatically requiring large amounts of cereal-based concentrates. Conversely, if you have an “easy keeper,” the conversation should start with your hay analysis and total calorie intake, not the novelty of the forage.

The Defining Feature: Condensed Tannins (and Why They Matter)

Sainfoin’s condensed tannins are central to both its potential benefits and its cautions.

Condensed tannins can bind proteins and other compounds. In ruminants, this can improve nitrogen utilization and reduce bloat risk. In the parasite research space, condensed tannins from sainfoin have been linked—across laboratory and animal studies—to effects on gastrointestinal nematodes such as reduced egg hatching, impaired larval development, and reduced larval motility. Importantly for horse owners, these effects are often correlated with tannin concentration and tannin structure, and they vary by plant variety (accession) and processing method. Source discussing equine and in vitro findings: https://pubmed.ncbi.nlm.nih.gov/23639199/?utm_source=equiniction

In practical terms, tannins are not “good” or “bad” by default. They’re active compounds that can shift outcomes depending on dose, the rest of the ration, and whether medications are being administered.

Sainfoin and Parasites in Horses: What Studies Suggest (and What They Don’t)

Interest in sainfoin for horses often spikes because owners hope it can replace or reduce chemical deworming. The research does not support that conclusion. What it does support is more nuanced: sainfoin can exert measurable anti-parasitic pressure under some conditions, but the magnitude and consistency of fecal egg count (FEC) reductions are often modest and variable.

Controlled trials in naturally infected horses have evaluated diets containing dehydrated or pelleted sainfoin, sometimes replacing portions of concentrate ingredients. In some trials, higher inclusion rates (including short-term diets where sainfoin pellets contributed a large share of dietary dry matter) were associated with changes seen in coproculture assays—such as reduced larval development or reduced larval motility—and at least one study observed a transient reduction in fecal egg counts in a higher-dose group. However, other studies found little or no consistent reduction in average fecal egg counts compared with controls. A clear synthesis of this “sometimes, but not reliably” pattern is discussed here: https://www.cambridge.org/core/journals/animal/article/are-sainfoin-or-protein-supplements-alternatives-to-control-small-strongyle-infection-in-horses/A6D451C792C75E1B97FABD8C86996AD5?utm_source=equiniction

So, how should you interpret that as a horse owner?

Sainfoin may help create a less parasite-friendly environment for some life stages (especially free-living or developing stages) and may reduce larval vigor in measurable ways. But adult worm populations and egg output are influenced by many factors—existing parasite burden, immunity, season, stocking density, manure management, and more. That’s why sainfoin is best framed as a possible supportive tool within an evidence-based parasite control program, not a replacement for one.

The Most Actionable Caution: Sainfoin Can Alter Ivermectin Absorption

One of the most important and directly actionable findings in the research is that sainfoin’s condensed tannins can change the pharmacokinetics of orally administered ivermectin. In a controlled trial, horses consuming dehydrated sainfoin pellets had lower plasma ivermectin concentrations, and egg reappearance after treatment occurred sooner than in control horses. This indicates that feeding a high-tannin sainfoin product around the time of treatment may reduce exposure to the drug—potentially affecting efficacy and shortening the egg reappearance period. Source: https://pubmed.ncbi.nlm.nih.gov/35929352/?utm_source=equiniction

This matters because ivermectin (and related macrocyclic lactones) are widely used in equine parasite control. If a feed ingredient measurably reduces drug absorption, the downstream risk is not theoretical: it can complicate how you interpret treatment response and may contribute to earlier egg shedding after deworming in some circumstances.

If your horse’s program includes routine oral dewormers—especially ivermectin paste—do not assume a “natural” forage addition is neutral. The safest approach is to tell your veterinarian you’re introducing sainfoin (especially pelleted/dehydrated forms at meaningful inclusion rates) so deworming timing and follow-up testing can be adjusted if needed.

Hay vs. Pellets vs. Silage: Why Form and Processing Change Results

Not all sainfoin products behave the same way, because preservation and processing can change tannin availability and other bioactive characteristics.

Research indicates that drying temperature, ensiling, and pelleting influence how much condensed tannin remains extractable and how the forage ferments when exposed to equine hindgut inocula. That means “sainfoin hay,” “sainfoin silage,” and “dehydrated/pelleted sainfoin” are not interchangeable if your goal is to predict tannin activity or compare your feeding plan to a published trial. Source: https://www.sciencedirect.com/science/article/pii/S0377840123001748?utm_source=equiniction

This also helps explain why owners sometimes hear dramatically different anecdotes: one barn adds a little sainfoin hay and sees no measurable change in FEC trends; another uses a concentrated pelleted product and notices shifts in coproculture or post-treatment egg patterns (especially if they were monitoring closely). The processing, inclusion rate, and baseline parasite management context can be completely different.

If you’re shopping for sainfoin pellets, look for supplier transparency on nutrient testing and—ideally—condensed tannin information, because the “bioactive” aspect is one of the main reasons people choose sainfoin in the first place.

Is Sainfoin Safe for Horses?

Under normal feeding conditions, sainfoin is generally considered safe and palatable for horses, and published equine studies report good acceptance of sainfoin hay and pellets. There is not a body of evidence showing a typical “toxicity syndrome” in horses fed sainfoin as forage at conventional levels. Feedipedia also notes the overall attractiveness and usability of sainfoin as pasture, hay, silage, or pellets. Source: https://www.feedipedia.org/node/703?utm_source=equiniction

The primary safety consideration supported by current equine evidence is not classic toxicity—it’s interaction risk. Condensed tannins can bind dietary constituents and pharmaceuticals. The ivermectin interaction is documented in horses, so it should be treated as a real-world management variable, not a footnote.

Other cautions are more “good feeding practice” than sainfoin-specific: introduce it gradually, monitor manure consistency and appetite, and ensure the overall ration still meets mineral requirements (especially if you’re making multiple diet changes at once).

How to Use Sainfoin for Horses in a Practical Feeding Program

Most published equine trials that explore parasite-related outcomes use short-term feeding periods and relatively high inclusion of dehydrated/pelleted sainfoin compared with what many barns would do long-term. In real management, sainfoin is more commonly used as one component of the forage base (mixed hay) or as a supplement (pellets) rather than the sole forage source. Source discussing trial patterns and practical caution: https://www.cambridge.org/core/journals/animal/article/are-sainfoin-or-protein-supplements-alternatives-to-control-small-strongyle-infection-in-horses/A6D451C792C75E1B97FABD8C86996AD5?utm_source=equiniction

If your goal is general nutrition (not parasite pressure), sainfoin can be approached much like other higher-quality forages: start with a forage analysis, introduce gradually, and balance the ration to your horse’s body condition, workload, and health history (insulin status, ulcers, etc.). If your goal includes parasite support, your best tool is measurement: monitor fecal egg counts over time and coordinate changes with your veterinarian.

Introduce sainfoin gradually over 7–14 days, especially if switching from a very different forage base.
Ask your supplier for nutrient analysis; if the product is marketed for its bioactive properties, request condensed tannin information when available.
Decide what role it plays: forage base (hay/mixed hay) versus supplement (dehydrated sainfoin pellets)—these are not equivalent from a tannin-availability standpoint.
If you rely on oral macrocyclic lactone dewormers, avoid making a major sainfoin increase right at treatment time without a plan for follow-up monitoring.
Track outcomes that matter: body condition, topline, manure quality, and parasite metrics (FEC trends and, when appropriate, fecal egg count reduction testing).

Parasite Control: Where Sainfoin Fits (and Where It Doesn’t)

Sainfoin is best viewed as a potential adjunct to modern parasite control—not a replacement. Evidence suggests it can apply some anthelmintic pressure, especially in larval development or motility measures, but in vivo reductions in fecal egg counts are inconsistent and often modest. Source: https://pubmed.ncbi.nlm.nih.gov/23639199/?utm_source=equiniction and https://www.cambridge.org/core/journals/animal/article/are-sainfoin-or-protein-supplements-alternatives-to-control-small-strongyle-infection-in-horses/A6D451C792C75E1B97FABD8C86996AD5?utm_source=equiniction

Practically, that means:

If your barn already uses targeted selective treatment (TST) with regular fecal egg counts, sainfoin may be something you trial while keeping the rest of your program stable—so you can actually interpret changes. If your barn does not test, adding sainfoin and hoping it “handles parasites naturally” is a gamble, and it may also confuse interpretation of drug response if you deworm at the same time.

Owners who want to operationalize this without guesswork often use a fecal egg count test kit (or submit samples through their veterinarian or a lab) before and after major management changes. The point isn’t to “prove” sainfoin works in a single horse; it’s to maintain parasite control while exploring supportive strategies.

Video: Sainfoin Overview

If you want a quick visual overview of why people are excited about this forage, this video is a helpful starting point:

Questions to Discuss With Your Veterinarian Before Making Big Changes

Because the strongest “watch out” in the literature is the drug interaction signal (not a toxicity signal), it’s worth having a short, specific conversation with your veterinarian—especially if your horses are on timed deworming or if you’re evaluating early egg reappearance after treatment.

If we increase sainfoin (especially pelleted/dehydrated forms), should we adjust the timing of oral dewormers like horse ivermectin dewormer?
Should we run a fecal egg count reduction test (FECRT) after the next treatment to confirm expected drug efficacy?
How will we interpret “earlier egg reappearance” if we change the forage base at the same time?

What We Still Don’t Know: Evidence Gaps Worth Respecting

Sainfoin research for horses is promising, but it’s not complete. Many equine studies are relatively short-term and frequently use specific processed forms (notably dehydrated/pelleted products) and inclusion rates that don’t always match typical long-term feeding at home. Outcomes also differ depending on sainfoin variety, harvest maturity, and processing—variables that change condensed tannin concentration and biological activity. A practical overview of condensed tannin preservation considerations is discussed here: https://dellait.com/sainfoin-forage-hay-or-silage-for-preserving-condensed-tannins/?utm_source=equiniction

Most importantly, the documented ivermectin interaction underscores a broader gap: we need more data on how tannin-rich forages may interact with other equine medications and supplements. Until that evidence exists, the safest approach is simple: avoid making multiple major changes at once, and measure what you care about (body condition, manure quality, FEC trends, and post-treatment response) when introducing a bioactive forage.

Bottom Line: When Sainfoin for Horses Makes Sense

Sainfoin can be a highly palatable, nutrient-dense forage option that may offer modest parasite-related benefits in certain contexts. It’s most compelling for owners who are already committed to monitoring—through forage analysis and fecal testing—because that’s how you turn an interesting forage into a managed, evidence-aligned part of the program.

The key caution is also the clearest: significant sainfoin intake, particularly from dehydrated/pelleted sources, may reduce plasma concentrations of orally administered ivermectin and shorten egg reappearance time after treatment. If you use sainfoin, do it deliberately, coordinate with your veterinarian, and confirm your deworming program is performing as expected.