Efforts to improve the management of forage storage are good investments, said Karla Hernandez, SDSU Extension Forage Field Specialist.
"Hay, haylage or silage preservatives will reduce storage losses from molds, bacteria and fungi especially when the forage is harvested at higher moisture levels," Hernandez said. "Limited microbial growth occurs in dry hay, generates a small amount of heat, and usually raises temperatures very slightly (Fig. 1 below)."
Dry matter and crude protein digestibility are reduced by excessive microbial growth explained Hernandez.
"Excessive microbial growth can raise temperatures to 130 to 150oF, increasing dry matter loss and producing Maillard reactions that reduce dry matter and crude protein," she said. "Effective preservatives to inhibit microbial growth or artificial drying to remove excess moisture help to avoid quality and yield loss in moist hay."
Hernandez said effective hay preservatives include: organic acids, buffered acids, ammonia sources, like anhydrous ammonia or urea, inoculants and enzymes. Each are described below:
Organic acids (propionic and acetic acids): inhibit mold growth and will help to reduce heating and dustiness in hay. Their effectiveness in hay depends on the application rate of active ingredients and moisture content. Application rates near 10 pounds per ton are needed for hay with 20-25 percent moisture, while 20 pounds per ton are needed for wetter hay with 25-30 percent moisture. Some issues with the use of organic acids are related to late season mold growth. Mold inhibition of acid products tends to decrease after long periods of hay storage. The acid eventually dissipates during storage while the moisture remains in the hay.
Buffered acids (Ammonium propionate and propionic acid; Fig. 2 below): are effective in control heating in moist hay but corrosiveness, high acidity, and difficult working conditions has limited their use.
Ammonia sources (Anhydrous ammonia or urea): effective reducing microbial growth in moist hay and can improve fiber digestibility by acting on lignin-carbohydrate bond in cell walls. However, it is important to recommend ammoniating low quality roughage for forages with less than 5 percent crude protein and 45 percent of total digestible nutrients (TDN). Ammoniating higher quality forage can cause toxic compounds to be formed. In terms of livestock component, ammonia increases non-protein N, which can help to meet the protein needs for a dairy or beef cattle. Anhydrous ammonia is an effective preservative for hay containing less than 30 percent moisture. As for urea, it is safer to handle than anhydrous ammonia and has similar benefits for storage and fiber digestibility. Relatively large amounts (5-7 percent of estimated bale weight) of urea applied during baling can be effective up to 30 percent moisture. However, treated hay must be covered or processed with a bale wrapper.
Inoculants: bacterial inoculants (i.e. lactic acid) are being promoted as an alternative to chemicals for improving hay preservation. How does it work? Bacteria is added to water and sprayed on hay as it is baled. The bacteria multiply and grow during the early stages of forage preservation (after baling) and help to preserve the hay. These products can be used in hay with moisture content of 25 percent moisture. Interestingly, not a lot of research has been done in order to examine their effects in large rectangular bales over a range of moisture contents. Research suggests that lower moisture content may be necessary to be effective for safe storage.
Enzymes (cellulose, amylose, and lactobacillus): These enzymes promote plant cell breakdown and render the cellulose and starch more accessible to desirable acid-producing bacteria.
Figure 1: Typical storage temperature profiles in dry and moist hay. A brief elevation in temperature could occur during the first couple of days in hay at 20% moisture. Hay with higher moisture level will reach higher temperatures and heating might be prolonged. Source: Collins and Owens, 2002.
Figure 2: Effect of moisture or ammonium propionate preservative on heating small square bales. Source: Collins M, 1995.