Quick answer: Dry-matter loss for a round bale stored outside on the ground runs 15–25% over six months per multi-state forage research (Univ. of Wisconsin Extension A3677, Univ. of Tennessee SP437-A, USDA ARS data). The single biggest variable is ground contact, not bale shape or wrap type. Five storage methods, ranked by typical 6-month loss: barn (2–5%) → tarped on gravel (4–8%) → net-wrapped outside on gravel/pallets (5–10%) → net-wrapped outside on dirt (10–15%) → twine on dirt (15–25%).
Last updated: May 27, 2026
Storage loss is rarely a single decision. It's a stack of five — ground surface, wrap type, stacking pattern, exposure direction, and how long the bale sits before feeding. Get four of them right and you keep dry-matter loss in the single digits; get all five wrong and a quarter of the bale is gone before the cow ever sees it.
This guide compares the five practical storage methods on six-month dry-matter loss, capital cost, and labor — drawing on three university-extension references and one USDA dataset. Numbers below are ranges, not single points, because forage species, climate, and bale density move them.
Why Storage Loss Happens
Three loss mechanisms account for almost all of it:
- Ground contact wicking. Soil holds moisture year-round in most climates. A round bale resting on dirt continuously absorbs water from the bottom, feeding microbial activity inside the bale. Wisconsin research (UW Extension A3677) shows ground-contact loss alone accounts for 5–10% of bale dry matter over six months — before any UV or rainfall factor is added.
- Rainfall infiltration. A bale exposed to 30+ inches of annual rainfall absorbs water in the top 6 inches of the outer layer. That layer rots, drops in feed value, and pulls density from the bale.
- UV breakdown. Polyethylene degrades under sunlight. If net wrap or twine fails before feeding, the bale loses shape, becomes hard to handle, and exposes more surface to weathering. UV breakdown only matters if storage runs longer than the wrap's rated life.
The Five Storage Methods Compared
| Method | 6-mo DM loss | Per-bale cost (200 bales/yr) | Best for |
|---|---|---|---|
| Inside a barn or shed | 2–5% | $3–$8 amortized | High-value hay (alfalfa, dairy-quality) |
| Tarped on gravel pad | 4–8% | $1–$2 (tarp life) | Mid-volume operations without a shed |
| Net-wrapped, on pallets/gravel | 5–10% | $1.20–$1.50 (wrap) | Volume operations rotating bales within 6 months |
| Net-wrapped, on bare ground | 10–15% | $1.00–$1.20 (wrap) | Short-term storage only — under 90 days |
| Twine, on bare ground | 15–25% | ~$0.50 (twine) | Avoid for storage longer than 60 days outdoors |
The numbers reflect 6-month outdoor storage in a continental US climate (30–45 in annual rainfall). Sources: UW Extension A3677, UT Extension SP437-A, USDA ARS forage-loss studies.
What the Studies Actually Show
Net wrap reduces loss only when ground contact is also handled
A 2014 UT Extension study compared net-wrapped and twine-tied round bales stored side-by-side on bare ground. After six months, net-wrapped bales lost 14% dry matter; twine-tied bales lost 22%. The net wrap helped — but not enough to make outdoor-on-dirt acceptable. The same study tested net-wrapped bales on gravel pads with similar weather exposure and recorded 6.5% loss. The gravel/pallet decision moved more dry matter than the wrap choice did.
Stacking pattern matters more than orientation rules
Older guidance recommended orienting bales north–south for sun exposure. Recent extension data (UW A3677, 2020 revision) finds the orientation effect is small (under 1% DM) compared to the spacing effect. The cleaner rule: single-row, no stacking, 12+ inches between bales for airflow, runoff channeled away from the row. Pyramid stacking traps water on lower bales and roughly doubles their loss rate — the upper bales shed water onto the lower ones, exactly the failure mode the 2011 Mississippi State pyramid-storage study documented.
Dense bales weather better than fluffy ones
A higher-density bale (12–14 lb/ft³) loses about half as much dry matter as a lower-density bale (8–10 lb/ft³) under the same conditions. Density is set by baler chamber pressure and forage moisture at baling — not by storage. If your baler tends toward soft bales, storage method has to compensate for it.
Decision Guide by Operation
- High-value hay (dairy alfalfa, premium horse hay): Indoor storage is the only acceptable answer. The 2–5% DM advantage over outdoor methods is worth $15–$40 per bale at typical 2026 hay prices. Storage shed amortization pencils out under 5 years for any operation rotating 200+ bales/year.
- Mid-volume cow-calf operation (50–500 bales/year): A gravel pad (3–4 in crushed limestone or geotextile) plus tarp or quality net wrap puts loss in the 5–10% band. The pad costs $200–$500 to build and lasts indefinitely. This is the sweet spot for outdoor storage.
- Volume operation (500+ bales/year), 6-month or shorter storage: Net-wrapped bales on gravel or pallets, single-row, runoff channeled away. Factory-direct net wrap with verified 12-month UV resistance keeps the wrap intact across the storage cycle; verify the spec sheet calls out an ASTM G154 or DLG accelerated-weathering test, not just "UV-stabilized" language.
- Short-term storage (under 90 days), no infrastructure: Net wrap on bare ground is acceptable. Sales pressure to feed within 90 days is real. Loss accelerates fast after that.
- Custom-baler / contract work feeding within 30 days: Twine is fine. Storage loss isn't the cost center; baler-load time is.
What to Verify Before Building Outdoor Storage
Before committing to a method, three measurements decide whether it's worth doing:
- Site drainage. Stand on the site after a 1-inch rain. If water pools, the pad will fail. Move the site or grade the pad with a 2% slope away from a runoff channel.
- Annual rainfall for the storage window. NOAA climate data is the reference. Above 35 inches annual rainfall, outdoor storage past 6 months is rarely viable without indoor space.
- Bale handling cycle. If bales will be moved more than twice between baling and feeding, net wrap on gravel beats tarps — tarps tear during handling. If bales sit still until feeding, tarps are cheaper.
Loss is a process, not an event. The numbers in the table assume the bale was wrapped well, sat on a surface that drained, and didn't get moved into a worse environment partway through. Skip any one of those and the loss numbers move into the next band down.
Inline photo: Reeder Creek Ranch, CO by inkknife_2000, licensed under CC BY-SA 2.0 via Wikimedia Commons.
