Corn Silage in Beef Production

Historically, corn silage varieties were selected for their grain and dry matter yield capabilities. Recent work at Ridgetown College - University of Guelph has indicated that corn silages can also greatly differ in whole plant digestibility. A trial conducted in 1996 evaluated 5 varieties based on their chemical analysis and measurements of beef steer performance in the feedlot.

Two silages were harvested at a very similar dry matter and starch percentage. Cattle fed the more digestible silage gained an additional 0.4 pounds per day and were also more feed efficient. A significant increase in external fat cover was also observed for cattle fed the more digestible silage.

The following parameters should be considered when a variety is selected for silage:

(a) Grain yield is still important.

Silages that are higher in grain content are usually a more concentrated source of energy for the ruminant animal. An increase in dietary starch content will increase the energy available for gain while reducing the amount of ration needed per kilogram of weight gain. A variety's grain yield potential should be considered when a hybrid is being selected for silage.

(b) Silages that are more easily digested should be selected.

Whole plant digestibility estimates can vary greatly between silages. In vitro measurements of digestibility are used to mimic the digestive process in the live animal's digestive system. Acid detergent fibre, neutral detergent fibre and lignin levels may also be used to rank silages on their available energy content, although caution must be exercised. Plant digestibility estimates should be considered when varieties are selected for high forage feeding programs.

(c) Select varieties with high dry matter (tonnage) yield capabilities.

A variety's (dry matter) yield potential should be a major consideration if a livestock producer is interested in maximising returns from his available land base. Yield potential is a very important silage characteristic!

Corn Silage for Growing Diets

Many factors should be considered before a feeding program is implemented for the growing phase (600 to 900). A consistent, high quality end product (properly finished carcass) should also be a high priority for all cattle feeding enterprises. Cattle gains are strongly related to the energy content of the diet. In theory, higher energy rations (measured by NDF and total digestible nutrient - TDN) should increase feedlot gains if other nutrients (like protein) are balanced in accordance to the diet's energy level. Ration C growth rate results could be achieved by feeding a 60 to 70 percent (DM) corn silage diet. The level of grain corn in the diet to maximise economic returns will depend on relative feed prices, overhead costs per day, cattle prices etc.

Corn Silage in Finishing Rations

Corn silage is not only useful in the growing phase diet, but also can play a role in the finishing diet. Marbling and fat deposition can be manipulated by diet, but they are also very highly a function of genetics.

Very high grain diets, especially ones that are of small particle size, leave animals at a high risk of developing acidosis. Using a small amount (10 to 20 percent of the diet) of high quality, long-cut corn silage in this case is an option to increase and improve rumen function. This is in preference to using roughages such as straw, stover or hay as the corn silage is higher in energy.

Often, the need for feeding such an extreme diet is to achieve an acceptable level of finish on animals that have excessive lean growth. By using a moderately higher energy diet during the growing period, the opportunity to use such feeds as corn silage in the finishing phase increases. The feeding of corn silage as opposed to first-cut hay when wintering yearling calves provides the energy required for setting up such a process.

If the animal in question deposits fat easily (marbling genetics and early maturing such as a British or British cross) and is not excessively lean upon feedlot entry it appears more corn silage can be fed. Recent research has indicated that a higher level of corn silage (up to 50% of finishing rations) may be fed, resulting in similar performance but more economical feed cost per pound of gain than a diet with higher corn grain. The silages in these experiments have been those of very high quality (high grain content as well as high whole plant digestibility).

Using the Feed Analysis of Your Corn Silage

The most important fact in the use of your analysis is the quality of the lab! Ensure the lab is an accredited one, and that equipment is routinely calibrated. Projections on beef or milk per acre must also be treated with caution, as these are projections made using standard management, feeding and feed assumptions all hinging on ADF values. As a result, a corrected TDN may be used. It is known as a Weiss TDN or WTDN. The Weiss values use lignin, cellulose and fat content in the sample to help correct for the lack of information yielded by ADF-only extrapolations.

Planning Rations Using Corn Silage

Ensure that ration formulation programs or advice are derived from the databases of "The Nutrient Requirements of Beef Cattle, Seventh Revised Edition, 1996". This is a publication and model system developed by the National Research Council. Corn and corn silage tend to be low in protein, relative to the requirements of cattle. It is more important than ever to ensure sufficient protein. Although true protein sources may be used in the diet (soybean meal, corn gluten, animal by-products), non-protein nitrogen sources may be useful. This takes advantage of the rumen organisms' ability to fix nitrogen into protein, but is best used in high forage diets. Urea is toxic if the rumen cannot take advantage of it, so it must not be fed to animals with under-developed rumens nor overfed to animals that can utilise it.

Planning Your Crop

There is no magical process for determining acreage (or hectares) of corn silage required for the feeding operation. However, the following equation will allow the feed budget to be determined:

¤total feed = # head fed x lbs. gain per head x feed conversion

¤total corn silage required = total feed x % corn silage in ration ÷ 100

Summary

Corn silage is an excellent feedstuff for the production of beef. Its strength relative to grain corn is that it allows for greater beef production per acre. Corn silage can be used effectively in growing rations or in accelerated backgrounding. However, the success of corn silage inclusion in the finishing diet depends on the level of fat cover of animals at the 900 - 950 lb. mark. For successful use in finishing rations, received cattle must not have been excessively backgrounded on low quality feeds and the animals must not be too lean. If a good job is done of managing the weaned calf's growth curve, high quality corn silage can be an important and economical feed from weaning to slaughter.