Ammonia gas can be added to both dry and ensiled forages. This fact sheet will discuss ammoniation of lower quality dry forages such as straw, mature grass hay and corn stover. This technique offers no advantage for treatment of legume hays, and often may result in a toxic feed for livestock when high quality, immature forage grasses, sudangrass or small grain hays are ammoniated. The ammoniation of silage is described in Agronomy Facts AGF-018 (Silage Additives).
Lower quality forages are treated with ammonia for two reasons. First, ammonia, as described in AGF-013 (Hay Preservatives), is an effective preservative for hay containing up to 30% moisture. Secondly, treatment of mature grass hays and poorer quality crop residues is a cost-effective way of improving their feeding value. Ammoniation increases crude protein (CP) and improves forage digestibility.
When anhydrous ammonia is added to a dry forage (which still contains approximately 10% water), most of the ammonia becomes dissolved in the water within the plant forming ammonium hydroxide. Ammonia treatment increases the CP content of forages because anhydrous ammonia contains 82% nitrogen (512% CP), and between 50 and 80% of the added nitrogen is retained in the forage. About half of the retained nitrogen remains in the form of ammonia. Some of the retained nitrogen is converted by microbes present on the forage into microbial protein. Another fraction of the retained nitrogen is bound in an unknown manner to the forage fiber components.
How ammonia treatment increases digestibility is not completely understood. Ammonia treatment substantially reduces the concentration of neutral detergent fiber (NDF) in forages. Most of the loss of NDF is due to destruction of hemicellulose. Ammoniation also reduces the amount of lignin in some forages. Ammonia treatment disrupts chemical linkages between lignin and hemicellulose. Lignin inhibits fiber digestion; therefore, disruption of those linkages makes the hemicellulose more digestible. Cellulose digestibility also increases since lignified hemicellulose encases cellulose. Ammonia treatment also changes the physical characteristics of forages making them more pliable and increases their uptake of water (hydration). Hydration rate has an important role in digestion rate; the faster a forage particle is hydrated, the faster it is digested.
The amount of anhydrous ammonia necessary to improve digestibility is between 2 and 4% of the dry matter. This is equivalent to 1.8 to 3.6% on an as fed basis. In general, treating forages with about 3% (60 lbs./ton as fed basis) anhydrous ammonia produces the most economical benefits. For forages and residues that contain between 20 and 30% water, about 2% ammonia (as fed basis) is probably adequate. Hays containing more than 30% water should not be ammoniated. Both large round bales and conventional small bales can be ammoniated using the same method. Stack bales (weigh a few bales first) on plastic or concrete (stacking the forage on the ground results in less retention of added nitrogen since the ground can absorb ammonia). Stacks should be 3 bales high for large round bales (3-2-1 pyramid) and 8-10 bales high for small square bales. The width of the stack should be the same as the height. The stack can be as long as desired, but a small gap (about 1 foot) should be left in the stack every 30 to 40 feet for an application hose or pipe. After stacking, the forage is covered with a piece of black plastic (6-8 mil thick). The edges of the top plastic and bottom plastic must be sealed tightly. The best way to do this is to place the top plastic over the bottom plastic and roll the two together, then cover the roll with soil or gravel. The holes cut for the application pipe should also be sealed tightly around the pipe. The effectiveness of the treatment is related directly to how well the plastic is sealed. To calculate how many pounds of ammonia will be needed, multiply the number of bales in the stack by the average bale weight and then multiply by 0.03. Order an anhydrous ammonia nurse tank with that many pounds of ammonia. For very large stacks, several tanks may be necessary. Connect the nurse tanks to the application pipes and apply the ammonia slowly (approximately 50 lbs/minute). After the tank is empty disconnect it from the application pipes and allow the forage to remain covered for at least 3 weeks. The reaction between ammonia and fiber is dependent on temperature, so if forages are treated with ammonia during cold weather a 5 week treatment period should be used. Forage can remain covered for longer periods without problems. The hay should be uncovered carefully so that the plastic can be reused which reduces treatment cost considerably. Some people recommend that the forage be left uncovered for 3 to 5 days prior to feeding to allow free ammonia to escape. This generally is not necessary, but sometimes animal acceptance may be poor initially if ammoniated bales are not aired out prior to feeding.
Anhydrous ammonia is a toxic gas. Proper ammonia safety precautions must be followed. Work in a well ventilated area up wind from application area. Goggles and gloves should be worn for protection during application. Also have ample clean water available to promptly rinse ammonia off eyes and skin surfaces.
THE ONLY DRIED FORAGES THAT SHOULD BE CONSIDERED FOR 3% AMMONIATION ARE STRAWS, MATURE GRASS HAY AND CORN STOVER. Alfalfa and other legume forages exhibit negligible improvement from ammonia treatment. High quality grasses such as immature orchardgrass, fescue, and sudangrass, and cereal grain hays should not be ammoniated above 1% because the resulting product is often toxic to livestock.
Ammonia treatment (3%) of dry forages generally increases the CP content by about 8 percentage units. Ammoniated straw will contain 12-14% CP as compared to 4-6% for untreated straw. The CP content of ammoniated mature grasses can be increased to 18-20% compared to the 8-12% for untreated hay. Dry matter digestibility of straws can be enhanced by 10 to 20 percentage units by ammoniation. Improvement of 5 to 10 percentage units in dry matter digestibility of mature grasses usually occurs following ammoniation. Ammonia treatment also increases animal consumption of low quality forages. The increase in digestibility coupled with the increase in feed intake results in a substantial increase in consumption of digestible energy by animals fed ammoniated forages as compared to those fed untreated forage. In general, ammonia treatment of straw increases the feeding value to that of low to medium quality grass hay. In other words, ammoniated straw can provide adequate energy and protein to maintain cattle and sheep under most conditions. Ammoniated mature grass hay is generally adequate in energy and protein for lactating beef cows and ewes. When using ammoniated straw or mature grass hay, pay attention to mineral and vitamin supplementation. Vitamin A and sulfur adequacy should be examined closely. The value of ammonia treated low quality forages to dairy cattle is not known. Since the energy requirements of lactating dairy cows are quite high, the amount of ammoniated low quality forages included in the diet should be limited.
It will cost $11 to $19/ton to ammoniate hay. This cost includes the price of ammonia plus the cost of plastic. If plastic can be used more than once, the cost will be reduced considerably. The cost of ammoniation must be added to the cost of the original forage. The total cost of the ammoniated forage then should be compared to low quality alfalfa hay (14% CP). Because wheat straw is expensive relative to its feeding value, ammoniation of straw is usually not economical. Ammoniation of low quality grass may be cost-effective depending on the price of alfalfa.
Assistant Professor, Dairy Science
District Agronomy Specialist
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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