Corn Silage Management

Silage Management
Lance Kennington, Ph.D. CHS Nutrition

Introduction When harvested and preserved correctly, silage is a valuable ingredient in diets for beef and dairy cattle, and sheep. Ensiling forages such as corn, sorghum, small-grains (barley and wheat), alfalfa and grass provides the animal with a good source of digestible fiber. Corn, sorghum and small-grain silages also provide grain needed for fast and efficient growth. However, if silage is preserved in a haphazard way, large economic losses due to spoilage and subsequent reductions in silage quality can occur. Few producers realize how much money is wasted through energy losses and reduced animal performance due to spoilage. This problem has become more prevalent since silage preservation has moved from upright airtight silos to horizontal concrete bunkers and drive over piles. This article will recommend procedures necessary to properly preserve silage quality during storage and feed out.

Silage fermentation process
Producers who feed corn silage need to understand the importance of eliminating oxygen from the pile as soon as possible after harvesting. During the initial stages of fermentation, the aerobic bacteria associated with the plant will continue to use carbohydrates and oxygen for their own growth. From a preservation standpoint, this is a very inefficient process. Carbohydrates in the corn plant that could potentially be consumed by cattle or sheep for energy will be digested effectively by these aerobic bacteria for energy. This aerobic process results in rotten silage. Therefore, eliminating as much oxygen as possible from contacting the silage is essential. Oxygen exposure to the silage can be reduced by harvesting the silage at the correct moisture content, chopping to the correct length, tightly packing the silage in the bunker, and covering the silage with plastic. After an oxygen-free environment is achieved, anaerobic bacteria predominate, which are the organisms that are needed to preserve the silage. Anaerobic bacteria in the silage pile will produce lactic acid, which will drop the pH to a low level and bacteria will not be able to grow. As long as no oxygen is allowed to penetrate the pile, the silage will be preserved.

Silage preservation practices
Moisture content
Table 1 contains harvest recommendations for different silage types. Silage that is too wet will produce too much seepage and runoff and will favor poor fermentation. Silage that is too dry will not pack in the bunker very well, resulting in a lack of oxygen elimination and spoiled silage. Monitoring the corn kernel starch milk line is a good indicator that silage harvest should commence since kernel maturity is related to corn whole-plant moisture content. When the corn kernels are filled approximately one-half to two-thirds with starch the silage moisture content will usually be between 65 and 72%. If silage harvest time is lengthy, it may be necessary to begin harvest at one-half starch content to ensure the silage does not become too mature and dry when the last load is harvested. When harvesting alfalfa and grass silage, achieving the correct moisture content is critical. If these types of silage are allowed to ferment at higher moisture content, poor fermentation can lead to clostridial organisms growing in the silage.

Stage of Maturity
Monitoring maturity at harvest is also an important part of silage management since studies have shown that although grain content increases with advanced maturity, stover digestibility decreases. Therefore, to obtain optimal grain and stover digestibility, it is important to harvest silage at the proper stage of maturity. The proper stage of maturity for the majority of hybrids appears to be when corn kernels are one-half to two-thirds filled with starch.

Chop length
Proper chop length is essential in the packing process. If chop length is too long, the silage will not pack very tight and eliminating oxygen from the pile will be difficult, resulting in spoiled silage.

Packing
Improperly packing silage at harvest can cause extensive dry matter losses in silage. To avoid these losses, harvested material should be spread in thin layers (6 to 12 inches) over the entire surface and packed. Allow the tractor to pack the entire layer before adding more silage. Be sure to pay attention to the edges. Edges are commonly neglected and can allow oxygen to enter the pile if not properly packed. Weight should be added to the tractor to aid compaction.

Covering the silage with plastic
A lot of producers feel it is unnecessary and expensive to cover their silage piles with plastic to keep oxygen from penetrating the pile. Many feel the 6 to 12 inch crust left on top of the pile is worth less than the time and money spent to seal the entire pile. Researchers involved in silage preservation have observed the following about silage left uncovered

. . . . if left unprotected, dry matter losses in the top 1 to 3 feet can exceed 60 to 70%. This is particularly disturbing when one considers that in the typical "horizontal" silo, 15 to 25% of the silage might be within the top 3 feet. When the silo is opened, the spoilage is only apparent in the top 6 to 12 inches of silage, obscuring the fact that this area of spoiled silage represents substantially more silage as originally stored. Producers who do not seal need to take a second look at the economics of this highly troublesome "technology" before they reject it as unnecessary and uneconomical. The loss from a 40- x 100-foot silo filled with corn silage can exceed $2,000. Loss from a 100- x 250- foot silo can exceed $10,000 (Bolsen et al., 2001).

An additional concern associated with unsealed silage is the management necessary to deal with the rotten crust on the silage piles. Many producers feel this rotten material can be diluted with the well-preserved silage and the resulting mixture will not negatively affect performance. However, in a recent study at Kansas State University (Table 2), silage researchers found mixing the rotten layer with good silage will decrease intake and digestibility of corn silage. Diets consisted of 90% silage and 10% protein and mineral supplement. Dry matter intake of cattle consuming well preserved corn silage was 16% greater than cattle eating a 75% spoiled:25% well-preserved silage blend. This increase in intake coupled with a 10% greater organic matter digestibility for the well-preserved silage will amount to a large economic advantage for the producer.

Inoculants
Inoculants are sometimes used to ensure enough lactic acid producing bacteria are present on the silage to produce a rapid pH drop and fast, effective preservation conditions. Research has shown these inoculation products will decrease dry matter losses, even in covered bunkers. These products are particularly useful in alfalfa, grass and small-grain silage situations to help prevent clostridial diseases associated with poor fermentation conditions. It is important to remember that inoculants will not prevent losses associated with poor management practices. In other words, it is more important that silage be harvested at the correct maturity and moisture content and properly packed and covered with plastic in a well-designed bunker than to depend on inoculation to correct problems.

Feedout
Management of the bunker face is also critically important in minimizing losses. If feedout is too slow, oxygen will be able to penetrate the pile and cause heating and spoilage. During the cool times of the year, a minimum of 6-12 inches per day should be removed from the face to minimize oxygen penetration and energy losses. During the hot summer months, the amount of silage removed should be increased to 12-18 inches per day. When using a loader to remove silage from the pile, scrape the face from the top to the bottom. If the loader bucket is used from the bottom up, it can create fissures through the pile, which allow oxygen to penetrate far inside the pile and cause rotten seams of silage to appear. Keep the silage face cleaned up by feeding all the silage falling from the pile. This will help to minimize energy loss due to heating.

Conclusions
Silage will continue to be an important feed resource well into the future. Following good silage management practices at storage and feedout will ensure dry matter losses will be minimized. The Nutrition Consultant in your area can assist you in developing a silage management program to fit your operation.

Table One

Table Two