How To Store Round Bale Hay for Horses Safely

By Dr Duncan Houston

Round bales can be a brilliant option for horse owners.

They are convenient, cost-effective, lower labour, and useful when feeding multiple horses through colder months or during pasture shortages. But round bales also have one major weakness: if they are stored badly, they can quietly turn from useful forage into expensive compost.

The problem is not just wasted money. Poorly stored hay can become mouldy, dusty, less palatable, lower in nutritional value, and unsafe for horses with respiratory disease. In some cases, poor-quality round bales can also increase serious health risks, including colic, equine asthma flare-ups, and botulism concerns. (University of Minnesota Extension)

A round bale is not safe just because it is big, wrapped, or still mostly green.

The real question is: was it made dry, stored dry, kept off the ground, protected from weather, and checked before feeding?

Quick Answer

Round bale hay should be stored under cover whenever possible, kept off direct ground contact, placed on a well-drained surface, protected from rain, and checked for mould, heat, dust, dead animals, and spoilage before feeding to horses. Outdoor round bale storage losses can range widely depending on storage method, with uncovered bales stored directly on the ground showing some of the highest losses. (SDSU Extension)

For horses, the health concern is bigger than the waste bill. Do not feed mouldy, dusty, rotten, wet, contaminated, or suspicious round bales, especially to horses with asthma, chronic cough, colic history, poor immunity, or botulism risk. (University of Minnesota Extension)

Why Round Bale Storage Matters

Hay is not dead just because it has been baled.

Moisture, heat, air exposure, ground contact, humidity, insects, rodents, and weather all affect what happens to the bale during storage. If moisture gets into the bale, mould and spoilage can develop. If the bale sits directly on wet soil, moisture can wick upward from the bottom. If bales are stacked badly outdoors, water can become trapped between bales and slow drying. (University of Minnesota Extension)

For cattle, some weathered hay may still be used in certain situations. Horses are less forgiving.

Horses are more sensitive to dusty and mouldy forage from a respiratory point of view. The University of Minnesota Extension is blunt: do not feed mouldy hay to horses, because mould spores can produce respiratory disease, and dust from mould spores can contribute to recurrent airway obstruction, now usually discussed under equine asthma. (University of Minnesota Extension)

In practice, this is the part owners underestimate.

A bale can look acceptable on the outside but have wet, sour, mouldy, or spoiled sections inside. That is especially important with large round bales because the inside can be harder to inspect properly before horses start eating into it.

How Much Hay Can Be Lost Through Poor Storage?

Storage losses are not tiny.

South Dakota State University Extension summarises dry matter loss ranges across multiple studies. The lowest losses occur with hay stored under a roof, plastic wrapped, or sleeved. The highest losses occur with uncovered bales stored directly on the ground. (SDSU Extension)

Storage method	Potential dry matter loss
Under roof	2% to 10%
Plastic wrap on ground	4% to 7%
Bale sleeve on ground	4% to 8%
Covered, rock pad or elevated	2% to 17%
Uncovered, rock pad or elevated	3% to 46%
Uncovered, on ground, net wrap	6% to 25%
Covered, on ground	4% to 46%
Uncovered, on ground	5% to 61%

That is not just a farm accounting issue. It changes what the horse actually receives.

A bale with a weather-damaged outer layer may have lower usable dry matter, poorer palatability, more waste, more dust, and more spoilage. The University of Minnesota notes that the outer 4-inch layer of a 6-foot round bale contains about 25% of the bale’s total volume, and this outer layer is most vulnerable to weather damage if the bale is not protected. (University of Minnesota Extension)

So when a bale is stored badly, you are not losing “a bit of outside hay.”

You may be losing a large part of the bale.

The Best Way To Store Round Bales

The best option is simple: store round bales under a roof, on a dry, well-drained surface, with good airflow.

A hay shed, pole barn, covered structure, or well-ventilated storage area gives the best protection from rain and ground moisture. Indoor storage can reduce round bale storage loss substantially compared with outside storage. University of Minnesota Extension reports that indoor storage usually reduces storage losses by about two-thirds. (University of Minnesota Extension)

The ideal storage system has:

• A roof

• Good ventilation

• No leaks

• No direct soil contact

• Rodent control

• Wildlife control

• Easy access to older hay first

• Space to inspect bales

• Safe separation from horses if dust or mould is present

Do not stack hay under a leaky roof and feel smug because it is “inside.” A wet roof leak is just weather with better manners.

If You Must Store Round Bales Outside

Outdoor storage can work, but it needs planning.

The priorities are:

• Keep bales off wet ground

• Choose a well-drained site

• Avoid shade

• Avoid low-lying areas

• Cover bales if possible

• Store round bales end-to-end

• Space rows for airflow

• Do not trap moisture between bales

• Feed the oldest bales first

• Check bales regularly

University of Minnesota Extension recommends storing outdoor round bales on a well-drained surface, avoiding trees and low-lying areas, covering bales stored outside, and storing round bales end-to-end rather than stacked in ways that trap moisture. (University of Minnesota Extension)

South Dakota State University Extension also recommends placing bales in north-south rows with 3 to 4 feet between rows, storing bales on a slight slope or well-drained rock pad, and avoiding shade so the sun can help dry bales after rain. (SDSU Extension)

The goal is not just covering the top.

The goal is stopping water from entering from above, below, and between bales.

Why Ground Contact Is Such a Problem

Round bales stored directly on soil or grass can absorb moisture from the ground.

That bottom layer may become damp, mouldy, sour, or rotten even if the top of the bale looks acceptable. University of Minnesota Extension notes that bales resting on the ground can absorb enough moisture to grow mould, and that gravel, old tires, or wood pallets can help prevent soil moisture from wetting the hay. (University of Minnesota Extension)

This is why a rock pad, pallets, tires, concrete pad, or well-drained raised base can make such a difference.

A good base should:

• Drain water away

• Reduce soil contact

• Allow airflow under or around the bale

• Prevent bales from sitting in mud

• Keep the bottom layer from rotting

For horses, I would much rather see fewer bales stored properly than a huge supply of hay slowly turning into mouldy paddock furniture.

Should You Use Tarps, Bale Sleeves, or Plastic Wrap?

Yes, if they are used properly.

A good plastic cover can reduce round bale storage loss by about half, and storing round bales inside can reduce loss even more. (University of Minnesota Extension)

Plastic wrap, bale sleeves, tarps, and specialised covers can all help, but only when they are secured properly and do not trap moisture underneath.

The cover needs to:

• Shed rain

• Stay tight in wind

• Allow the bale area to dry

• Avoid pooling water

• Avoid trapping humidity against wet hay

• Be inspected after storms

A loose tarp flapping over a bale pile can become a moisture tent, not a storage solution.

Very dramatic. Not very useful.

Should Round Bales Be Stacked?

If round bales are stored outside without cover, stacking is usually a problem.

Stacking tends to trap moisture and reduces the drying effect from sun and wind. University of Minnesota Extension recommends storing round bales end-to-end when stored outside and notes that stacking large round bales outdoors usually increases losses. (University of Minnesota Extension)

South Dakota State University Extension also warns that pyramid stacking can create high dry matter losses because water shed from upper bales flows down into the bales below. (SDSU Extension)

If bales must be stacked outside to save space, cover the pile properly and monitor it closely.

For horse hay, I am conservative. If storage increases mould risk, it is not worth the space saved.

Moisture, Mould, and Heat Damage

Moisture is the enemy.

Horse-quality hay should be baled at appropriate moisture levels. University of Minnesota Extension states that horse-quality hay should generally be baled between 10% and 15% moisture, that hay baled over 17% is at risk of moulding, and that large round bales should be baled at 15% moisture or less to reduce mould risk. (University of Minnesota Extension)

Wet hay can also heat. Very wet hay can become a fire risk, especially when tightly packed. Illinois Extension notes that bales over 20% moisture are at risk of heating and combustion, and that temperatures over 170°F are a serious danger. (Illinois Extension)

For horses, heat-damaged hay may also be less nutritious and less palatable. If hay smells caramelised, tobacco-like, sour, musty, or mouldy, it deserves closer inspection before feeding.

Why Mouldy Round Bales Are Dangerous for Horses

Mouldy hay should not be fed to horses.

Mould spores can irritate the respiratory tract and contribute to equine asthma, coughing, nasal discharge, reduced performance, and heavy breathing. University of Minnesota Extension specifically says not to feed dusty or mouldy hay or grain, and recommends reducing dust exposure by feeding lower, improving airflow, using dust-free bedding, feeding outside, soaking dusty hay where appropriate, or replacing hay with hay cubes in severe cases. (University of Minnesota Extension)

Round bales can be particularly problematic because horses often bury their noses into the bale as it hollows out. AAEP notes that feeding from round bales can be poor for equine respiratory health because the horse may keep its nose in a deep hay cavity for long periods, creating an unhealthy breathing zone. (AAEP)

This does not mean every round bale is bad.

It means round bales need to be clean, dry, good-quality, fed in the right setup, and removed if they become dusty, mouldy, or spoiled.

Botulism Risk and Round Bales

Botulism is rare compared with common hay-waste problems, but it is serious enough to respect.

UConn Extension explains that botulism is caused by toxins produced by Clostridium botulinum and can cause muscle weakness, inability to swallow, recumbency, respiratory failure, and death. Their prevention guidance specifically warns against feeding poor-quality round bales, especially if they were baled with excessive moisture, and recommends not allowing round bales to be exposed to weather. They also note that spoiled material can be internal in round bales, so bales may need to be opened to check quality. (extension.uconn.edu)

They also recommend that, if round bales are fed, the amount should be consumed within about one week to reduce the chance of horses eating mouldy feed. (extension.uconn.edu)

This is a big point for small groups.

One or two horses slowly picking at one large round bale for weeks is not the same as a larger group eating through a clean bale quickly. The longer the bale sits exposed to weather, saliva, manure, mud, rain, and hoof traffic, the higher the spoilage risk.

Risk Framework: How Worried Should You Be?

Low Risk

This is usually lower risk if your round bales:

• Were baled dry

• Are stored under a roof

• Are kept off the ground

• Smell fresh and clean

• Have no visible mould

• Have no heat, sour odour, or damp core

• Are protected from rodents and wildlife

• Are fed in a clean, dry area

• Are eaten within a reasonable timeframe

• Are being fed to horses without respiratory disease

This hay still needs inspection, but the storage setup is sensible.

Moderate Risk

This is more concerning if your bales:

• Are stored outside but covered

• Are stored on pallets, gravel, or a rock pad

• Have some weathering on the outer layer

• Are net wrapped but still exposed

• Sit for weeks before feeding

• Are fed to a small number of horses

• Are sometimes damp on the bottom

• Have mild dust when opened

These bales may be usable if the inside is clean, dry, and fresh, but they need regular inspection and spoiled sections should be removed.

High Risk

This is high risk if your bales:

• Are stored uncovered on soil or grass

• Sit in mud or low-lying areas

• Are under trees

• Are stacked outdoors without adequate cover

• Smell musty, sour, or rotten

• Have visible mould

• Have wet or slimy areas

• Have dead animals, rodent contamination, or bird droppings

• Are fed to horses with asthma, cough, or poor immunity

• Take more than one week for horses to consume during wet conditions

These bales should not be casually fed to horses. Open and inspect them carefully, and discard questionable hay.

Critical

This is urgent if horses eating round bales develop:

• Colic signs

• Sudden feed refusal

• Diarrhoea

• Coughing or breathing difficulty

• Nasal discharge

• Weakness or trembling

• Difficulty swallowing

• Drooling

• Recumbency

• Sudden depression

• Signs of botulism

• Multiple horses becoming unwell after eating the same bale

Remove the bale immediately and call a vet.

When Is This an Emergency?

Hay-related problems become urgent when the horse is clinically unwell, not just when the hay looks questionable.

Call a vet urgently if your horse has:

• Colic signs

• Repeated pawing, rolling, flank-watching, or sweating

• Sudden refusal to eat

• Severe coughing

• Laboured breathing

• Nostril flaring

• Heavy abdominal effort while breathing

• Feed or saliva coming from the nose

• Difficulty swallowing

• Drooling

• Weakness

• Trembling

• Stumbling

• Recumbency

• Sudden severe depression

• Multiple horses affected at the same time

Botulism red flags include weakness, inability to eat, drooling because the horse cannot swallow, stiff short-strided walking, stumbling, loss of tail tone, recumbency, and respiratory failure. (extension.uconn.edu)

If several horses become sick after eating the same round bale, remove the bale and preserve a sample for possible testing. Do not keep feeding it while you “see how they go.”

What Else Can Look Like a Hay Storage Problem?

Not every problem after feeding a round bale is caused by storage, but poor hay should always be considered.

Important rule-outs include:

• Equine asthma from dust or mould

• Choke from coarse or stemmy hay

• Colic from poor water intake

• Impaction colic

• Sand intake around feeding areas

• Botulism

• Mycotoxin exposure

• Toxic weeds in hay

• Rodent or wildlife contamination

• Dental disease causing poor chewing

• Poor hay nutritional value causing weight loss

• Parasites

• Gastric ulcers

• Pasture changes

• Grain or supplement changes

• Viral or bacterial respiratory disease

This is why the hay history matters.

If a horse starts coughing, losing weight, refusing hay, colicking, or developing nasal discharge after a new round bale is introduced, do not ignore the timing. Open the bale, inspect the core, smell it, check for mould and foreign material, and consider changing forage immediately.

What Should You Do Next?

1. Inspect Every Bale Before Feeding

Do not judge only from the outside.

Check:

• Smell

• Colour

• Dust

• Mould

• Dampness

• Heat

• Foreign objects

• Dead animals

• Rodent contamination

• Weeds

• Rotten or slimy sections

• Tightness and density of the bale

University of Minnesota Extension recommends inspecting the inside of at least one bale before buying hay and not feeding mouldy hay to horses. (University of Minnesota Extension)

2. Store Bales Off the Ground

Use:

• Pallets

• Crushed rock pad

• Concrete pad

• Old tires

• Treated timbers

• A properly drained base

Avoid soil, grass, mud, and low areas where water pools.

3. Cover Bales Stored Outside

A proper tarp, bale sleeve, plastic cover, or weather-resistant wrap can reduce losses, but it must be secured and checked.

Covers should shed water, not trap condensation.

4. Store Bales End-to-End

For outdoor storage, end-to-end rows are usually better than stacking.

Leave enough space between rows for airflow and sunlight. University of Minnesota Extension recommends spacing adjacent lines at least 3 feet apart when more than one line is used outdoors. (University of Minnesota Extension)

5. Avoid Trees and Low Ground

Trees drop moisture, leaves, branches, bird droppings, and shade. Shade slows drying after rain.

Low ground collects water.

Both are bad hay storage decisions dressed as convenience.

6. Feed Bales Quickly Enough

For horses, round bales should not sit in the paddock for weeks becoming a weather station, toilet, bed, and buffet.

UConn Extension recommends feeding an amount that horses can consume within one week if round bales are used. (extension.uconn.edu)

This matters especially in wet weather.

7. Use a Proper Round Bale Feeder

A feeder can reduce trampling, manure contamination, mud contact, and waste.

For horses, choose a feeder designed with equine safety in mind. Avoid sharp edges, trapping points, low openings, or designs where legs, heads, halters, or shoes can get caught.

8. Remove Spoiled Sections Immediately

If a section is mouldy, wet, sour, dusty, slimy, or contaminated, remove it.

If the spoilage is widespread, remove the entire bale.

Trying to “just feed around the bad bit” is how a small hay problem becomes a vet problem.

9. Be Extra Careful With Respiratory Horses

If your horse has asthma, heaves, chronic cough, nasal discharge, poor performance, or dust sensitivity, round bales may not be the safest option.

Consider:

• Small square bales with lower dust

• Steamed hay

• Soaked hay where appropriate

• Hay cubes

• Hay pellets

• Feeding from a low, clean position

• Better ventilation

• Low-dust bedding

AAEP stresses that environmental management is central to equine asthma control, and that hay is one of the first sources to consider when reducing respirable dust. (AAEP)

Common Mistakes Owners Make

Storing Round Bales Directly on the Ground

This is one of the biggest causes of bottom spoilage. Moisture wicks upward and damages the bale from below.

Assuming Net Wrap Means Weatherproof

Net wrap helps bales hold shape and shed some water, but it does not make a bale immune to weather, ground moisture, or long-term outdoor spoilage. University of Minnesota notes that net wrap can reduce losses compared with twine, but outdoor storage still needs good site selection and protection. (University of Minnesota Extension)

Feeding Mouldy Outer Layers

If it is mouldy, do not feed it to horses. Removing a small weathered outer layer may be fine if the inside is clean, but do not let horses dig through mould to reach better hay.

Letting One Bale Sit Too Long

A round bale sitting for weeks in a wet paddock is asking for trouble, especially with small numbers of horses.

Storing Under Trees

Trees create shade, falling debris, and slower drying. It feels practical until the hay starts growing its own ecosystem.

Ignoring the Inside of the Bale

Round bales can hide internal spoilage. Open and inspect suspicious bales.

Feeding Round Bales to Asthmatic Horses Without Thinking

A clean bale in an open paddock is one thing. A dusty round bale that horses bury their noses into is another. Respiratory horses need a stricter plan.

How To Prevent Round Bale Problems

The best prevention plan is boring and effective.

Do this:

• Buy dry, dense, good-quality bales

• Ask how and when the hay was baled

• Avoid hay baled too wet

• Store under a roof where possible

• Keep bales off the ground

• Use a rock pad, pallets, or concrete

• Cover outdoor bales properly

• Avoid trees and low-lying ground

• Store round bales end-to-end outdoors

• Space rows to improve airflow

• Use older hay first

• Inspect bales before feeding

• Remove mouldy or spoiled hay

• Use safe round bale feeders

• Feed bales quickly enough

• Keep rodents and wildlife out of storage

• Avoid feeding round bales to horses with severe asthma unless the hay and setup are genuinely low-dust

• Call your vet if multiple horses become sick after a new bale

The cheapest hay is not the hay with the lowest purchase price.

It is the hay your horses can actually eat safely.

Will My Horse Be Okay?

Most horses do well on round bales when the hay is clean, dry, properly stored, fed in a safe feeder, and eaten before it spoils.

The risk rises when bales are wet, mouldy, dusty, stored on the ground, left outside uncovered, fed slowly over many weeks, or given to horses with respiratory disease.

If your horse is bright, eating normally, passing normal manure, breathing comfortably, and the bale is clean and fresh, that is reassuring.

If your horse coughs, stops eating, develops colic signs, has nasal discharge, struggles to breathe, becomes weak, or multiple horses become unwell after eating the same bale, remove the bale and call your vet.

The bale may look like feed.

But if it is mouldy, dusty, wet, or contaminated, it is not feed anymore. It is a problem wearing hay-coloured clothes.

FAQs

Can horses eat round bales safely?

Yes, horses can eat round bales safely if the hay is clean, dry, mould-free, stored properly, and fed in a safe way. Round bales are riskier when they are stored outside uncovered, sit directly on the ground, become wet, or are fed slowly over long periods. (University of Minnesota Extension)

How long can a round bale sit out for horses?

Ideally, a round bale should be eaten quickly enough that it does not become wet, mouldy, trampled, or contaminated. UConn Extension recommends feeding an amount that horses can consume within about one week to reduce the risk of them eating mouldy feed. (extension.uconn.edu)

Is mouldy hay ever safe for horses?

No. Mouldy hay should not be fed to horses. Mould spores can cause respiratory disease, and mouldy feed may also reduce appetite and create other health concerns. (University of Minnesota Extension)

Should round bales be stored flat side down or on the round side?

For outdoor storage, round bales are generally stored on the round side and placed end-to-end in rows so they shed water more effectively. The site should be well drained, and the bales should be kept off wet ground where possible. (University of Minnesota Extension)

Are round bales bad for horses with asthma?

They can be. Horses with equine asthma are sensitive to dust and mould, and round bales can create a poor breathing zone when horses bury their noses into the bale. Horses with chronic cough or asthma often do better with lower-dust forage options and stricter environmental management. (AAEP)

Final Thoughts

Round bales can save time, labour, and money, but only when they are stored and fed properly.

A good round bale storage plan protects hay from above, below, and between bales. That means cover, airflow, drainage, elevation, rodent control, regular inspection, and using bales before they deteriorate.

For horses, the standard needs to be higher than “the cows would eat it.”

Clean hay supports weight, digestion, respiratory health, and performance. Mouldy, dusty, wet, or spoiled hay can create coughing, colic concerns, poor intake, botulism risk, and expensive problems that were avoidable.

Store hay like it matters.

Because for the horse eating it, it does.

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If you are unsure whether a round bale is safe to feed, or your horse has started coughing, losing weight, refusing hay, showing colic signs, or acting unwell after a new bale, ASK A VET™ can help you work through the warning signs and decide what needs urgent attention.