Making Sure Corn Silage Makes the Grade

Reliable and economic corn silages have pH levels under 4.0 and require lactic acids to ferment appropriately, writes Rory Lewandowski, of Wayne County Extension, Ohio.
calendar icon 10 September 2013
clock icon 5 minute read

Corn silage has the reputation as a reliable and economic feedstuff, writes Mr Lewandowski. Corn silage is widely used in ruminant livestock rations, particularly with cattle, but I have also seen it used with sheep as well.

A good thought to keep in mind is that the quality of the corn silage you produce this fall will affect your livestock for many months in to the future. Producing high quality silage depends upon good management practices at several different steps.

Corn silage is a fermented product. To be effective that fermentation must take place in an anaerobic (no oxygen) environment. The goal in this fermentation process is to achieve a pH of less than 4.0. This can be accomplished when air is removed as quickly as possible after chopping so that high concentrations of organic acids, predominantly lactic acid, are rapidly produced. This may sound simple, but implementation depends upon good decisions, harvest preparation, and some cooperation from Mother Nature.

The first and most critical step is that corn must be chopped at the right moisture or dry matter (DM) content. If you don't get this right, nothing else will matter. A DM range of 30-38 per cent is acceptable. Silage put into a bunker silo should be at the lower end of this range while silage put into upright silos should be at the upper end.

A dry matter range for a store like this should be as in the lower limits of the 30-38 per cent dry matter range, advises Mr Lewandowski. 

Corn less than 27 to 30 per cent DM does not ferment properly. It produces silage that often has high concentrations of butyric acid and can have a very low pH. This silage will have an unpleasant odor and animal DM intake will be reduced.

Corn chopped at higher than 40 per cent DM does not pack well. As a result it usually does not ferment adequately, resulting in low acid concentrations, heat damage and moldy silage. Starch digestibility is usually low, causing the silage to have less energy.

Silage harvest needs to start on the wetter end of the acceptable range because corn will gain DM content or lose moisture at a rate of between 0.5 to 1.0 percentage points per day. Rapid harvest is important to ensure that corn is chopped within the acceptable moisture range.

Chop length is a consideration for silage packing, feeding and animal performance. A three-eighths inch (3/8) theoretical length of cut (TLC) is recommended for corn at 32 to 36 per cent DM. When DM is under 32 per cent , a three-quarters (3/4) inch TLC is recommended and when DM content is above 36 per cent , a TLC of less than 3/8 inch is recommended. There is a reason that this is termed "theoretical". The actual cut length in the field can vary so operators should look at the actual chopped forage and make adjustments to get the correct chop length. One practice that can change these recommendations is kernel processing.

"The guideline for packing is that 800 pounds of packing weight is needed for each ton of silage delivered"

Kernel processing involves fracturing the corn kernels as the corn plant is chopped. Research results have consistently shown benefits in animal performance when kernels are processed adequately. The goal is to crack 90 to 95 per cent of the kernels and 70 per cent of those should be fractured to smaller than one-quarter of a kernel. When kernel processing is a part of the chopping process then TLC is typically increased to three-quarters of an inch.

One question that often comes up in any silage production discussion is whether or not to use a silage inoculant. There are 2 main types of inoculants; homofermenters and heterofermenters. Homofermenters contain Lactobacillus bacteria that produce lactic acid and heterofermenters contain Lactobacillus buchneri that produce lactic and acetic acid. The lactic acid promoting inoculants are used to increase silage quality by driving the silage pH down quickly and reducing DM loss during the fermentation process.

Dry matter loss during fermentation is higher with the buchneri type inoculants but feed out losses can be reduced. The buchneri inoculants are used to increase the aerobic stability of silage during feed out. The acetic acid produced prevents yeast growth. Bill Weiss, OSU dairy nutritionist located at the OARDC in Wooster says that his standard recommendation regarding inoculant choice is that if you have historically had problems with moldy silage during feed out or if the TMR ration gets hot in the bunk, then use the buchneri type. If neither of these is an issue, then use the lactic acid promoting type of inoculant. Regardless of which inoculant type is used, the key is to purchase high quality inoculants and to apply them correctly.

After DM content, the next critical step is the rapid removal of air by packing. As layers of forage are added to the silo or pile, they need to be driven over multiple times by heavy machinery. The goal is to achieve a silage density of 15 lbs. of DM/ft3 or higher. The density is directly correlated with oxygen exclusion within the silage pack and generally high silage density results in lower DM losses. The guideline for packing is that 800 pounds of packing weight is needed for each ton of silage delivered to the silo or pack. For example, if the harvest rate is 50 tons/hr. then the packing weight needed is 50 x 800 = 40,000 lbs. or 20 tons.

In addition to the packing weight, the thickness of the layer packed should be monitored. The optimum condition is to pack layers of 6 inches or less. Another piece of advice from Bill Weiss regarding packing is: If you think you have packed enough; pack some more.

The final important step is covering the bunker or silage pile. This should be done as soon as the bunker is filled and the final packing had been done. Covering prevents oxygen, weather and animals from getting into the silage pack. Covering reduces DM and spoilage losses. The recommendation is to cover with plastic of 6 to 8 mil thickness and weigh that plastic down, sealing the edges as well. University research trials have demonstrated that the oxygen barrier 2-step products have reduced losses more than covering with the 6 to 8 mil plastic.

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