Managing for High Quality Stored Forage

Mr. Rory Lewandowski, Agriculture Extension Educator, Wayne County, Ohio State University Extension

The forage harvest season is well underway, starting several weeks ago with some of the small grains, particularly cereal rye, and progressing into our more traditional forage legumes or legume/grass mixtures. Bill Weiss, Ohio State University dairy nutritionist located at OARDC in Wooster, says the three laws of forage harvesting are: 1) You can’t win, 2) You can’t breakeven, and 3) You can only lose. Therefore, harvesting high quality forage is dependent upon minimizing biological and mechanical harvest system losses. 

Although there are others, two important biological factors affecting forage quality are plant maturity and plant respiration losses after mowing. Forage maturity, in particular for our first harvest during May, is the number one determinant of forage quality. Once that forage plant moves into the reproductive growth stage, beyond bud formation in legumes and beyond boot stage in grasses, there is a significant decline in quality for each day of harvest delay. Research suggests that relative feed value (RFV) or relative feed quality (RFQ) values decline about 4 points per day. Rates of decline are not as steep in July and August. The point here is that there is a narrow window of opportunity during spring and early summer harvests for the producer to make high quality forage so observation and monitoring are important. Once the forage plant is cut, the priority is to dry it down to an acceptable harvest moisture as soon as possible.

After mowing, plants continue to respire at a significantly high rate until forage moisture falls below 60%. Respiration is essentially the loss of starch and sugar, which are 100% digestible. The majority of this respiration loss occurs in the leaves of the plant. Conditioning helps to increase drying of the stems but does not speed drying of the leaves. Average dry matter (DM) losses due to plant respiration after cutting are 4 to 5% but can be as high as 8% in some situations. According to Dan Undersander, Extension forage specialist at the University of Wisconsin, a 4% loss in starch and sugar raises neutral detergent fiber (NDF) by 3% and results in a drop of almost 20 points on the RFQ scale. Management practices that will minimize respiration losses include mowing early in the day to maximize sunshine and drying conditions, and very importantly, spread the forage in a wide swath that occupies 60 to 80% of the cutter bar to expose leaves to those drying conditions.

Besides these biological losses, there are losses due to the mechanical harvesting system involved with mowing, raking, tedding, baling, chopping, hauling and storage operations. Quality losses are highly correlated with leaf loss. The degree of leaf loss and shatter generally depends upon how aggressively the forage is handled and the moisture content at the time of the mechanical operation. The harvesting operation results in DM, crude protein, and digestible DM declines and increases in NDF.  Looking at DM only, average losses due to mowing are 3.0%, raking 5.0%, tedding 3.0%, and baling 4.5%. The upper end losses for each of these operations is double (or worse) of these averages. The drier the forage is when it is handled, the greater the possibility of increased leaf loss and shatter.

Regardless of the production system used, the goal is to avoid the quality losses caused by a rainfall event. The losses due to rainfall depend upon the amount and timing of the rain event. Research has demonstrated that a one inch rainfall on a forage close to being ready to bale in a dry hay system can cause DM losses of 8 to 17%, results in NDF content increases of 6% and TDN decreases of 7%. That same rainfall within a few hours after cutting will have a less detrimental impact. Wrapped hay (baleage) and chopped haylage (silage) systems result in harvesting at higher moisture contents that can reduce quality losses due to leaf shatter. These systems also work as a strategy to avoid losses due to rainfall by decreasing the time between mowing and harvesting 

One key to making high quality baleage is to harvest forage at the proper maturity stage and moisture range. Because the forage is not chopped, one concern with baleage is overly mature forages. These forages have more fiber and less soluble sugars, resulting in poorer fermentation and a higher pH, which increases the risk of toxin producing clostridial bacteria in the baleage. Small grains, such as cereal rye, oats, wheat, and barley, are particularly at risk when used for baleage after head formation. Harvest baleage in the 45% to 55% moisture range. Moisture above 67% increases the risk of spoilage organisms like clostridial bacteria. Included in that family are botulism organisms. Tightly packed, dense bales are necessary to exclude air and promote anaerobic fermentation. Finally, wrap bales with six or more layers of 1.5 mil plastic within 24 hours after baling; sooner is better. Many producers aim for wrapping within 12 hours of baling. 

The keys to good quality haylage production begins with harvest between 55 to 62% moisture. Chop the forage at 3/8 inch theoretical length of chop to help improve packing. Fill the silo quickly to limit surface exposure to air, and in bunker silos, pack to achieve greater than 44 lb/cubic foot of silage. Bill Weiss always says that when you think you have packed enough, pack some more. Seal the bunker silo with an oxygen barrier film within hours of finishing silo filling, and then cover it on top of that with a 6 mil plastic to reduce spoilage. Research has shown a return of about $8 for each one dollar invested in sealing a bunker silo.

In a dry hay production system, forage baled too wet will mold and heat in storage. As interior bale temperatures get above 150 degrees F, the risk of a hay fire greatly increases. At 175 degrees, a hay fire is imminent and you need to call the fire department. For hay made without the use of a preservative, safe moisture levels are 20% for small square bales, 15 to 16% for large round bales, and 13 to 15% for large rectangular bales. The goal for long-term storage and stability is a moisture content of 15% or lower. The larger and more densely packed a bale is, the less likely it is to lose moisture during storage and achieve stability, so the moisture at harvest becomes more critical.

Preservatives allow baling at higher moisture contents, but they have to be used correctly and there are limits. The most effective preservatives are propionic acid based.  Research shows that they are generally very effective at allowing forage to be baled between 20 and 25% moisture, they are iffy between 25 to 30% moisture, and none of them are effective above 30% moisture. The keys to making them work in their effective range include providing enough product and making sure application is even and uniform as the bale is being formed. You need 10 lb/ton of actual propionic acid on the hay for moisture levels below 25% and 20 lb/ton of actual propionic acid on hay for moisture levels between 25 and 30%. The other limit is that the effectiveness decreases over time because the acid volatilizes and dissipates from the bale.

(References are available on request)