Storing Hay to Avoid Shrink

by Haley Ruffner
13 September 2023 | [email protected] | 307.205.6628


As we become inundated with new hay crop throughout the United States, moving the final vestiges of last year’s hay has highlighted the difference that storage makes, both in terms of quality and shrink. Farmers who store their hay in fully-wrapped tarps or 3 to 4 sided barns can claim much the same quality and weight as when they put up their hay, but farmers with no tarps at all, open-sided barns, or top tarps only are finding that their bales weigh significantly less than they did at baling.  

Hay loss due to storage conditions varies greatly depending on climate, grade of hay, and condition at baling. In the dry San Luis Valley of southern Colorado, for example, hay stored outside untarped will have minimal damage even after sitting outside for a winter if it was put up below 15% moisture. It will be sun-bleached and may have a couple of inches of moisture damage on the top and bottom bales, but overall it will still make adequate cow-grade hay. In many cases, it may still even work for horses if top and bottom bales are removed first—the inside bales will very likely look the same as when they were put up. In wetter climates, though, the humidity and rain can saturate entire stacks and can deteriorate the hay beyond all usability except as a mulch product.  

The most common methods for storing hay are outside stored, tarped, fully plastic wrapped, and barn stored. Each method requires a different amount of labor and investment, which farmers must measure against the money they are losing or saving on changes in hay value and shrink. Bale size also impacts the amount of loss—smaller bales will take a greater proportion of shrink. 

Dry matter loss varies greatly depending on climate. For hay stored untarped on the ground, the percent loss ranges from 5 to 61. The low range would likely be for hay in dry, temperate climates, whereas the higher end would be more accurate in very wet regions. Even on the lowest end of the range, that means if you put up 2,000 tons of hay per year, you are losing 100 tons to shrink—that’s four or five truckloads’ worth of hay! On the high end of this range, over half the crop is lost to shrink. This measurement is significant for farmers to consider when they talk about sitting on large batches of hay in hopes of prices rising. Even in the event that prices do rise slightly over the period of a few months, the amount of shrink existing stacks will take in that period may cancel out any additional profit from prices rising.  

Storing hay under heavy-duty tarps is another popular option. Tarps can be rented and crews hired to tarp stacks, which is often a convenient option for stacks that cannot be transported to barns for storage. Many farmers even use old billboard signs as tarps, which can cut down on cost. However, the variation in how hay can be tarped makes it difficult to judge value retained using this method. Some farmers tarp their stacks thoroughly with high-quality, heavy-duty tarps that mitigate most shrink, while others may just top-tarp the stack, leaving the sides open to the elements. While full tarps are ideal to protect from all moisture as well as sun bleaching, top tarping alone will still protect against moisture damage from precipitation on the areas of the stack that are most susceptible to rain damage.  

Although building materials spiked during the first years of the pandemic, dissuading people from building hay barns, costs have lowered enough that building a barn for hay storage is worth looking into, at the very least. A three- or four-sided hay barn will almost negate loss entirely, but even a less-expensive structure with just a roof will work to preserve hay quality. Any structure built for hay storage should be placed in an area with good drainage to avoid moisture permeating the bottom bales.  

Fully plastic-wrapping bales offers another option for minimizing shrink without having to front the cost of building a hay barn. Forage that is baled at a higher moisture content (typically 40-60%) and then fully wrapped in at 6 or more layers of 1 mil plastic will begin a slow fermentation process that can produce high quality forage at a lower cost than dry hay. This option requires less time drying in the windrow, but it also poses challenges in handling bales that are wrapped without perforating the plastic, which lets in oxygen that will mold the hay quickly. 

For farmers, exploring all available options to calculate the cost of storage against shrink and the amount of value retained can make or break the year’s profit. The climate, the time frame in which they plan to move their hay, and the quality at the time of baling should all influence a farmer’s decision on which storage method to use. Decisions on storage are important and should be approached as a calculation of these factors rather than as an afterthought. The type of storage a farmer chooses to use can have just as much influence on the profit as the volume and quality of hay produced.



Haley Ruffner is a sales broker for Aden Brook, a lifelong equestrian, and an accomplished writer.


Sources and Further Reading:,increase%20the%20cost%20of%20hay.