Drought Corn Silage in Beef Cow Diets

Drought Corn Silage in Beef Cow Diets

Drought poses many problems for cow/calf producers that they need to manage through.

The low productivity of pasture and rangeland poses the challenge of how to best manage the cattle and maintain long-term viability of the grass resource.

The other challenge, especially in areas where year-round grazing is not an option, is how to economically secure feeds for the time when cows are fed harvested forage. In drought conditions, hays and alfalfas are usually expensive because yield is low and demand is high. Corn silage is a feed that we don't typically feed to beef cows. Corn silage is usually used in growing calf and feedlot diets because of its high nutritive value, especially energy. When hays and alfalfas are expensive, corn silage is a feed that cow/calf producers should consider.

Determining Cost per Pound of Nutrient of a Feed

When comparing feeds to use in your feeding program, know the nutrient (protein, energy, phosphorus, etc.) composition of possible feeds that can be used in the ration and compare them on a dollar per nutrient basis. When this pricing procedure is used, it is important to compare the feeds on the same moisture basis. The easiest way to compare different feeds on an equal moisture basis is to compare them on a 100% dry matter (D.M.) basis. Silage and grass hay are used in cow diets as an energy source.

Let's say, for example, we need to purchase energy for the winter feeding program and alfalfa was an option priced at $100 per ton delivered. The alfalfa tested at 57% TDN, 18% crude protein, and was 88% dry matter. The cost of alfalfa per pound of TDN on a 100% D.M. basis is $0.10/lb of TDN (2000 lb/ton x .88 x .57 = 1003 lb of TDN in a ton of alfalfa that is 100% D.M.; then $100/1003 lb of TDN = $0.0997/lb of TDN).

Let's compare this to drought silage that yielded 40 bu/acre. Regular silage is 72% TDN so let's put drought corn silage at 64.8% TDN (90% of regular silage) and the dry matter is 35% (moisture content is 65% or it is 65% water) and cost in the bunker silo is $50/ton. Using the same procedure as above, the cost per pound of TDN for corn silage is $0.11/lb of TDN (2000 lb/ton x .35 x .648 = 453.6 lb of TDN in a ton silage on 100% D.M. basis; then $50/453.6 lb of TDN = $0.11/lb of TDN).

Alfalfa and corn silage priced at these rates they are priced similar. If you had the equipment to put up and deliver corn silage to the cow herd, corn silage may be an alternative to alfalfa.

These are just examples of feed prices to show how to make the calculations. Use local prices to make the calculations.

Feeding Corn Silage in Cow Diets

Drought damaged corn silage would be considered a high quality forage at 64% TDN (9% crude protein). A gestating cow will easily consume about 2.5% of her body weight on a D.M. basis of corn silage. If the cow weighs 1200 pounds, she could consume on a daily basis 30 pounds of silage on a D.M. basis. If the silage is 35% D.M., this 1200 pound cow could eat 86 lb (30 lb/.35 = 85.7 lb) of silage daily. If she is fed a full-feed of silage and the silage is 64.8% TDN, she could consume 19 lb of TDN daily (30 lb of D.M. daily x .648 = 19.44 lb of TDN). If the 1200 lb cow is in the last 1/3 of gestation, her TDN needs are between 13 and 15 pounds of TDN. So at a full feed of silage, she is consuming more silage than is needed to meet her requirement.

You could "limit-feed" corn silage to meet her energy requirement. In this example, feed her 60 lb daily (21 lb of dry mater of silage x .648 = 13.6 lb of TDN D.M. daily needed to meet TDN requirement; then 21 lb of dry matter/.35 D.M. of silage = 60 lf of silage "as-fed") to meet her TDN requirement.

Consider adding 5 to 6 lb per head per day of low quality forage like straw or corn stalks. Adding 6 lbs of ground corn stalks (50% TDN, 5% crude protein, 88% D.M.) on a D.M. basis to the diet will help in mixing and delivering the silage. These cows should gain body condition under typical winter conditions. In addition, energy requirement will be exceeded and crude protein requirement would be very close to being met (2.2 lb per day required, 1.89 lb from silage, and 0.26 lb from corn stalks) that I would not add any extra to the diet. Add vitamins and minerals and, under typical weather conditions, the herd should perform well. After calving more energy and protein will be needed in the ration.

Pricing Drought Damaged Corn Silage

To estimate the value of drought damaged silage, what do you need to consider? Start by comparing it to regular, high grain corn silage.

One common rule-of-thumb for pricing regular silage is that one ton of silage in the bunker silo is worth ten times the price of a bushel of grain. Using this rule, when corn is worth $5.00 per bushel, then regular silage is worth $50 per ton.

Drought damaged silage has lower feeding value than regular silage but not as much as you might think. Silage from corn producing 5 bushels per acre or less will have about 75 percent of the feeding value of well-eared silage. Corn producing 40 bushels per acre is worth about 95 percent that of regular silage. The value of drought damaged silage in the bunker silo can be adjusted proportionately to regular silage using this information. Feed value stays high during drought because leaves and stalks retain many nutrients that normally go into the grain.

If the corn is still standing in the field, harvest costs must be considered. These can be as low as 4 to 5 dollars a ton when yields are high and near the bunker silo to over 10 dollars a ton for fields with lowered yields due to drought that are several miles from the bunker.

One final consideration might be to compare the silage to other potential feeds. If you have ensiled drought damaged silage, let it go through the 28-day fermentation period before opening up the pit for feeding. Consider sampling and testing the silage for moisture, % crude protein, TDN, and nitrates. Even though the ensiling process will reduce nitrates by 40 to 60 percent, still consider testing for nitrates if silage is going to be the major component of the diet.

Don't give up on your drought damaged corn. It still can make some useful and valuable silage.

Dr. Rick Rasby, Professor of Animal Science
Animal Science
University of Nebraska–Lincoln