What Is Horse Capillary Strength Powder and Does It Work?

Supplements for horses are nothing new—but one product that’s grown in popularity, especially among performance horses, is capillary strength powder. Often marketed as a support for circulation, respiratory function, and bleeding prevention, this supplement is commonly added to feed in powder form.

But what exactly is capillary strength powder? And does it live up to the claims?

In this post, we’ll break down what it is, who uses it, the ingredients it typically contains, and what current research (if any) says about its effectiveness. As with any supplement, knowing what’s in it and how it may affect your horse is key—especially when it’s used to manage serious symptoms like nosebleeds or signs of stress under heavy physical exertion.

If your horse has been showing vague symptoms or behavior shifts and you’re unsure what’s going on, start by reviewing early signs of illness before turning to supplements.

What Is Capillary Strength Powder for Horses?

Capillary strength powder (sometimes marketed as bleeder support or lung support powder) is a nutritional supplement promoted to help fragile blood vessels stay resilient during intense exertion. Trainers reach for it most often in high-speed sports—Thoroughbred and Quarter-Horse racing, barrel racing, polo, even eventing—where exercise-induced pulmonary hemorrhage (EIPH) is a recurring worry.

Typical Ingredient Profile

Core Component	Rationale	Evidence Snapshot
Bioflavonoids (hesperidin, rutin, citrus complexes)	Thought to improve capillary elasticity and reduce oxidative damage.	A 1984 JAVMA study found no statistical benefit of hesperidin–citrus bioflavonoids in preventing EIPH PubMed.
Vitamin C (ascorbic acid)	Antioxidant that can be depleted during heavy work.	Recent research shows IV vitamin C may modulate inflammatory responses in horses—but data in healthy athletes are sparse PubMed.
Vitamin K	Supports normal blood-clotting pathways.	A 2024 industry review notes no peer-reviewed evidence that oral vitamin K lowers EIPH incidence flairstrips.com.
Herbal extracts (yarrow, grape-seed OPCs, turmeric)	Added for natural anti-inflammatory or antioxidant activity.	Potency and standardisation vary widely between brands.

Internal tip: Before adding any supplement, establish a baseline for temperature, pulse, and respiration with our step-by-step guide to The Horse’s Vital Signs. Regular logs make it easier to judge whether a new product is actually helping.

Who Uses It and Why

• Performance horses under high cardiovascular strain, especially those with a history of EIPH or “bleeder” notation on race records.

• Proactive owners who want additional support alongside veterinary strategies such as furosemide, nasal strips, or higher-intensity conditioning programs.

• Horses in dusty or high-pollen environments where repeated airway irritation might inflame delicate capillaries.

Remember that EIPH is multifactorial; airway pressure surges, mechanical stress, and individual anatomy all play roles — supplements alone rarely solve the problem. The Merck Veterinary Manual’s overview of EIPH in Horses explains why veterinarians often combine medication, management tweaks, and equipment solutions.

Does Capillary Strength Powder Work?

Current peer-reviewed data are mixed at best. Early controlled trials failed to show significant reductions in bleeding episodes with flavonoid supplementation, and more recent papers focus on antioxidant status rather than direct EIPH outcomes. Until larger, modern studies appear, capillary strength powders should be viewed as adjuncts, not stand-alone cures.

If you decide to trial one:

1. Choose a brand with transparent labelling and third-party testing.

2. Track performance and post-work scopes or tracheal washes to see if bleeding scores actually change.

3. Review show-rules withdrawal times; certain vitamin K levels may trigger medication flags in some jurisdictions.

4. Pair it with environmental controls, such as covered feed, dust mitigation, and, if racing, the strategies outlined in our Potomac Horse Fever Case Studies (where proactive vital-sign tracking proved critical).

In short, capillary strength powder for horses can be part of a broader respiratory-health toolkit, but it is not a magic bullet. Consult your veterinarian, keep meticulous records, and combine nutritional tweaks with proven management practices for the best chance of protecting those hard-working lungs.

What Are the Claimed Benefits?

Manufacturers and some horse owners claim that capillary strength powders can offer a range of benefits, particularly for high-performance horses or those showing early signs of respiratory stress.

Here are the most commonly promoted benefits:

Reduces nosebleeds during exercise

Capillary-strength formulas are marketed to lessen post-work epistaxis in “bleeder” horses. The theory is that bioflavonoids reinforce fragile pulmonary capillaries so fewer rupture when lung pressures soar. A classic controlled trial, however, found no statistically significant drop in bleeding episodes after 90 days of a hesperidin-citrus flavonoid blend compared with untreated horses.

In other words, anecdotal success stories exist, but peer-reviewed data remain weak. For background on why those capillaries burst in the first place, see the Merck overview of exercise-induced pulmonary hemorrhage (EIPH)

Supports vascular and respiratory function

Because antioxidants such as vitamin C and grape-seed OPCs scavenge free radicals, makers suggest these powders keep small vessels elastic and bolster overall oxygen delivery. Human and small-animal studies show flavonoids can reduce capillary permeability, but comparable equine research is sparse, and most performance benefits are still theoretical. Establish a pre-supplement baseline with daily logs from The Horse’s Vital Signs so you can judge any real change in recovery times or stamina.

Promotes stronger vessel walls

Rutin and hesperidin are frequently cited for their collagen-stabilising effects, which could make capillary walls less prone to rupture during sprint efforts or big jumping efforts. Reviews of equine EIPH management note that flavonoid trials to date are small and inconclusive, emphasising the need for larger modern studies. Until then, think of the supplement as a possible assist, not a guaranteed shield.

Helps performance horses under stress

Hauling long distances, training in heat or at altitude, and repeated high-intensity workouts all raise cardiovascular strain. Riders often use capillary strength powder proactively in these situations, hoping to buffer oxidative stress. While that strategy hasn’t been rigorously tested, keeping a keen eye on appetite, attitude, and minor coughs with How to Tell if Your Horse Is Sick is the fastest way to see whether stress is taking a measurable toll.

Supports horses prone to exercise-induced pulmonary hemorrhage (EIPH)

EIPH is multifactorial—airway pressures, cardiac output, and individual anatomy all play roles. Current AAEP and Merck references list nutritionals like flavonoids as adjuncts at best and stress that proven interventions such as furosemide, nasal strips, and careful conditioning remain first-line tools. If your horse already scopes with blood, discuss a comprehensive programme (medication, management, and perhaps supplementation) with your veterinarian rather than relying on powder alone.

While some of these benefits are based on anecdotal feedback from riders, trainers, and grooms, it’s important to look at what the science says too—which we’ll cover in the next section. If your horse is showing signs of illness or subtle changes in behavior, it’s best to start with a full health check. This early signs of sickness guide is a great place to start.

Is It Commonly Used in Equine Care?

Capillary-strength powder has become a staple in barns where lung efficiency directly affects the scoreboard. While it is nowhere near as ubiquitous as electrolytes or joint supplements, you will find a tub of “bleeder support” on most feed carts in disciplines that push horses’ cardiorespiratory systems to the limit.

Where you’ll see it most

• Thoroughbred and Quarter-Horse race barns – Trainers often pair the powder with furosemide or nasal dilator strips to support horses flagged as “bleeders.” An industry survey reported routine supplement use in more than half of U.S. race stables managing exercise-induced pulmonary hemorrhage (EIPH).

• Barrel racers, eventers, and polo strings – Short, explosive efforts spike pulmonary pressures; riders add flavonoid blends in hopes of keeping capillaries intact. Product manufacturers such as Finish Line list these sports as primary targets for their formulas.

• Senior performance horses – Age-related vascular stiffness can hamper recovery in hot or high-altitude venues. Owners sometimes combine capillary blends with the low-impact conditioning ideas in our guide to The Basics of Equine Nutrition.

How it is typically fed

Credit: Finish line horse

Most brands come as a palatable powder mixed into the concentrate once or twice daily. Core ingredients—hesperidin, rutin, vitamin C—are sometimes bundled with extras such as grape-seed extract, turmeric, or joint nutrients, letting trainers replace multiple single-function products with one scoop.

Why it has gained traction

1. EIPH is common and performance-limiting – Large cohort studies confirm that even low-grade bleeding can dent race placings.

2. Low regulatory risk (when labelled correctly) – Unlike many respiratory drugs, flavonoid powders usually fall outside medication-control rules, though vitamin K levels must still be checked for FEI or USEF competition.

3. Easy to trial and monitor – Owners can track temperature, pulse, and post-work scope scores to judge efficacy. Use the worksheets in The Horse’s Vital Signs to document before-and-after data.

4. Marketing momentum – High-profile trainers and manufacturers publish testimonials and blog posts touting “stronger lungs” and “healthier capillaries,” adding social proof to scientific curiosity.

Caveats before you jump on the bandwagon

• Quality control varies – Independent labs have found some flavonoid products under-deliver on label claims. Ask for a certificate of analysis or choose brands that publish third-party testing.

• Adjunct, not cure – Peer-reviewed trials still show mixed results; furosemide, nasal strips, and conditioning remain first-line EIPH tools.

• Needs objective tracking – Without pre-supplement baselines, perceived improvements may just be placebo.

Bottom line: Capillary-strength powder is now common in high-intensity disciplines because it is easy to add and carries minimal rule-book baggage. Use it as part of an integrated programme—veterinary diagnostics, proven medications, good nutrition, and meticulous vital-sign records—so you can tell whether the powder is truly keeping those hard-working lungs in winning shape or simply adding cost to the feed bill.

What Does the Research Say?

When it comes to capillary strength powder for horses, the scientific backing is limited and somewhat mixed. While many of the ingredients—especially bioflavonoids and antioxidants—are supported by human studies, research specific to equine health is still emerging. For example, this research summary on flavonoids and capillary function (PubMed) suggests improvements in vascular integrity in humans, though more equine-specific trials are needed.

Limited clinical trials in horses

At present, there are very few peer-reviewed studies that directly examine the effectiveness of capillary strength powders in horses. Most existing data is either anecdotal or extrapolated from human and small-animal studies. This makes it difficult to say definitively how effective these supplements are for preventing bleeding or improving vascular resilience in equine athletes.

Supportive findings in human and veterinary research

Bioflavonoids like hesperidin and rutin have been shown in human studies to support vascular health, reduce inflammation, and improve capillary integrity. These compounds may be beneficial in horses as well, but more equine-specific studies are needed to confirm dosage, absorption, and overall impact.

Use in EIPH management protocols

Some veterinarians may recommend capillary support supplements as part of a larger protocol for managing exercise-induced pulmonary hemorrhage (EIPH)—a condition where horses bleed from the lungs during intense exertion. However, these supplements are typically used alongside prescription medications, not as standalone treatments.

Veterinary oversight is essential

Because of the lack of regulated studies and the variation in supplement formulas, it's important to consult your veterinarian before adding capillary strength powder to your horse’s routine. Certain ingredients could interact with medications or mask symptoms of underlying conditions, making it harder to catch problems early.

Supplements should never replace veterinary care. If you suspect your horse has respiratory issues, review our post on average horse heart rate and how to check it to identify potential warning signs.

If your horse is experiencing symptoms like recurrent nosebleeds, labored breathing, or behavioral changes under stress, it’s worth addressing those concerns with your vet first—before turning to supplements.

Are There Any Risks or Side Effects?

Capillary strength powders are usually marketed as “natural” and therefore harmless, but any product that influences blood flow, clotting, or inflammation carries caveats. Treat these supplements the same way you would a prescription drug: know the active ingredients, check compatibility with existing treatments, and monitor your horse’s vital signs so you can catch problems early.

May interfere with medications

Many formulas contain bioflavonoids, vitamin K, or herbal vasodilators. These can theoretically blunt or enhance the action of NSAIDs, furosemide, or other prescription options for exercise-induced pulmonary hemorrhage (EIPH). Before combining products, run the ingredient list past your veterinarian and, if you compete, confirm withdrawal times with your governing body’s medication rules (see current FEI guidelines on controlled substances).

Can mask symptoms

A slight drop in post-work nosebleeds or a mild uptick in stamina can lull owners into thinking the underlying airway or cardiovascular problem is solved. If performance is still below baseline, book an endoscopic exam instead of upping the supplement scoop. Track daily TPR with The Horse’s Vital Signs so you can separate placebo effect from true improvement.

Not a replacement for veterinary care

Capillary powders are marketed as support, not treatment. They do not replace veterinary diagnostics like tracheal washes, BAL cytology, or thoracic ultrasound. For horses already diagnosed with EIPH, first-line therapies such as furosemide or nasal dilator strips remain the evidence-based core.

Caution with certain conditions

Unbuffered vitamin C can irritate the stomach, and abrupt withdrawal after high-dose use can suppress endogenous ascorbate production. Horses with gastric ulcers, recent surgery, or known bleeding disorders should avoid high-acid or pro-anticoagulant blends unless your veterinarian signs off.

Conclusion

Capillary strength powder is a widely used supplement in the performance horse world, promoted for its ability to support vascular health, reduce bleeding episodes, and aid in respiratory resilience. While some of its ingredients are supported by research in humans and small animals, equine-specific data remains limited.

That doesn’t mean it’s without value—many riders and trainers report improvements when using it as part of a larger care routine. But as with any supplement, it should be used thoughtfully and under the guidance of your veterinarian.

If your horse is showing signs of respiratory stress, exercise-related bleeding, or discomfort during training, the first step is always to rule out medical issues. From there, capillary strength powder may have a role to play in keeping your horse performing at their best.

FAQ

Is capillary strength powder suitable for everyday horses or just performance horses?

While it’s most commonly used in racehorses and competitive athletes, some owners choose to use it for older horses or those with minor respiratory concerns. However, for non-performance horses without symptoms, there’s usually no proven benefit. Your vet can help determine if your horse would actually benefit from vascular support.

Can I give capillary support powder alongside other supplements like electrolytes or joint support?

In many cases, yes—but it depends on the product formulations. Some supplements share overlapping nutrients like vitamin C or bioflavonoids, which could lead to oversupplementation. Always review ingredient labels and consult your veterinarian to avoid potential interactions.

How long does a horse need to be on capillary support before seeing results?

Results vary widely. Some owners report improvements in a few weeks, while others see no change at all. If you don’t observe any benefit after 30 to 60 days, it’s worth re-evaluating your horse’s needs with a vet rather than continuing indefinitely.

Is capillary strength powder legal for competition horses?

Most products use naturally sourced ingredients and are generally considered legal. However, competition rules vary between organizations. If you compete under FEI, USEF, or breed-specific rules, confirm with your governing body to ensure compliance.

Can this supplement help with recovery after intense training or hauling?

Possibly. While not marketed as a recovery product, the circulatory support it offers may help horses bounce back more comfortably from stress. It should be used in addition to, not in place of, hydration, proper rest, and post-exercise care.

Does every horse with EIPH need capillary strength powder?

Not necessarily. EIPH is a serious condition that often requires veterinary management with medications and adjusted training plans. Capillary strength powder may help reduce symptoms in some horses, but it’s not a standalone solution and should only be part of a broader care plan.