Hay is dried forage, such as grasses or legumes, preserved for livestock feed. Determining how long hay can be stored before it spoils is not a fixed duration, but rather depends entirely on environmental conditions and the hay’s initial quality. Proper storage aims to retain the nutritional density and palatability of the feed for as long as possible. Poor storage practices accelerate degradation, reducing the economic value and potentially creating hazards.
Environmental Requirements for Maximum Storage Life
The most important factor governing the longevity of stored hay is the moisture content at the time of baling. To achieve the longest possible storage duration, forage must be thoroughly dried before being compressed. Small square bales should generally be baled at less than 22 percent moisture. Large round bales, which retain heat more effectively, require a lower moisture content, typically below 18 percent for safe storage.
Baling hay above these thresholds creates an internal environment conducive to the rapid growth of mold and bacteria. Once baled, the hay must be shielded from external water sources, including rain, snow, and moisture wicking up from the ground. Storing bales directly on concrete or soil allows capillary action to draw moisture into the bottom layers, initiating spoilage.
Placing bales on pallets or a thick layer of crushed stone helps create a barrier against this ground moisture and prevents significant dry matter loss. Proper stacking is another measure to manage the internal environment of the stack. Stacks should be arranged to maximize air circulation, which helps dissipate any residual heat or moisture trapped within the bales.
Good ventilation prevents the accumulation of warm, moist air pockets that encourage microbial activity and heat buildup. Managing the initial moisture and protecting the bales from subsequent wetting are preventative steps that significantly extend the useful life of the forage.
Nutritional Decline and Practical Timelines
Even when stored perfectly, hay quality begins to decline over time due to slow chemical changes, long before visible spoilage occurs. Most of the dry matter and nutrient losses happen within the first month or two of storage, primarily involving the loss of soluble carbohydrates. Hay stored under optimal conditions typically loses only about five percent of its original dry matter during the first year.
Practically, hay retains excellent feed value and palatability for a period of about six to twelve months after harvest. Beyond this timeframe, the forage is generally still safe to feed, but its nutritional density steadily decreases. Hay that is over a year old may have nearly the same protein and energy value as hay that is six to eight months old, assuming it has not been exposed to weather damage.
The most significant nutritional loss involves carotenes, which are precursors to Vitamin A, and they decline rapidly, especially when exposed to sunlight. Up to 80 percent of beta-carotene can be lost during the initial curing process, with an additional loss of about seven to ten percent per month of storage.
This decline means older hay may require supplementation to ensure animals receive sufficient Vitamin A, even if the hay looks acceptable. The rate of quality reduction is also influenced by the type of forage originally baled. Legume hays, such as alfalfa, often experience a faster degradation of protein and leaf material compared to grass hays like timothy or orchardgrass.
Identifying Spoilage and Fire Hazards
Several indicators signal that hay is no longer safe or suitable for feeding. Visible signs of spoilage include the presence of mold, which may appear as dusty white, blue-green, or black patches on the bales. Hay that has molded will also often present a musty, sour, or foul odor, which is a strong indicator of microbial growth and fermentation.
Excessive dustiness, even without visible mold, suggests the presence of microscopic fungal spores that can pose a serious respiratory hazard to animals. If any of these signs are present, the forage should be immediately separated from the rest of the supply and evaluated for safety.
A significant danger associated with improperly cured or stored hay is the risk of spontaneous combustion. Internal moisture content above safe limits allows bacteria and fungi to rapidly multiply. The metabolic process of this microbial respiration generates heat, which occurs in all hay baled above 15 percent moisture.
If the internal temperature of a stack reaches approximately 130 degrees Fahrenheit, a chemical reaction begins to produce flammable gases. Temperatures above 175 degrees Fahrenheit signal that a fire is imminent. Monitoring the core temperature of a stack is a necessary step in mitigating this serious hazard, especially within the first six weeks after baling, which is when most hay fires occur.