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1108 PD: High-priced corn and dairy cow rations

Published on 24 July 2008

Corn grain usually makes up 30 to 35 percent of the total ration dry matter (DM) of a typical Midwest lactating cow diet. Changes in its price, therefore, can have significant impact on total feed costs.

Even with high corn prices, however, it is unlikely that corn grain will be removed completely from the ration.

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Corn grain, due to its high starch content, permits the formulation of energy-dense rations required by cows with high genetic merit for milk production. Adequate starch concentrations in corn grain also promote growth of rumen bacteria and protozoa essential for optimum forage fermentation. On the other hand, too much starch in the rumen may result in sub-clinical or clinical rumen acidosis.

The low protein concentration in corn grain could be considered a disadvantage from a nutritional standpoint, although this feature turns out to work in the nutritionist’s favor.

Corn protein is deficient in the amino acid lysine. As a result, there is a need for high-quality forages (e.g., alfalfa) and co-products that will supply additional lysine in the diet. But if low-protein corn did not dilute the alfalfa and co-products, the protein requirements of the lactating dairy cow could be exceeded, and the excess protein would be excreted to the environment as nitrogen in urine and feces.

Corn can be considered an “ideal” feedstuff. But what if corn prices go up more than you want to see?

Economics of using corn and forages
According to the NRC (2001), a dairy cow producing 77 pounds of milk requires only 15.2 percent protein in the ration. If corn grain was to be replaced entirely by a high- protein co-product such as distillers grains (30 percent crude protein – CP), this would limit the alfalfa hay or silage that could be included, so that the protein and phosphorus requirements of the cow would not be exceeded.

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Corn silage then becomes a natural choice as the primary forage in rations where corn grain is partially removed. Corn silage is low in protein and provides fermentable starch, energy and relative amounts of effective fiber (depending on its particle size).

From a dairy producer’s economic standpoint, the question is whether – with the current corn prices and speculations about futures – increasing the acreage devoted to corn silage would be a sound economic strategy compared to corn planted for grain and sold as a cash crop.

A $1 increased per bushel of corn will increase the average dairy cow ration between 27 and 34 cents per day. This will affect various measures of economic return, including, for example, the milk-feed price ratio. This ration represents the pounds of 16 percent protein mixed dairy feed equal in value to 1 pound of whole milk. Whenever the ratio meets or exceeds 3.0, it is considered profitable to buy feed and produce milk.

The feed price is calculated using the following formula, and average corn, soybean and hay prices:
Milk price $ per hundredweight
––––––––––––––––––––––––
[(price of corn ($/bu)/56) x 50]
[(price of soybeans ($/bu)/60) x 8]
+ [(price of hay ($/ton)/2000 x 41)]

Although all three feedstuffs used in the calculation do not constitute an entire lactating cow ration, they are among the most common feedstuffs used to provide energy, protein and forage.

Importance of forage digestibility
If you plan to decrease grain supplementation and still sustain high levels of milk production, you need to select highly digestible forages. Forage fiber represents the largest nutrient fraction in a dairy ration. At the same time it presents the greatest variation in digestibility.

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In ruminant diets, this fraction is analyzed as neutral detergent fiber (NDF) and acid detergent fiber (ADF). The residue in the NDF is negatively correlated with feed intake.

Analyzing samples for NDF digestibility (NDFD) will provide an estimation of the energy the cow is able to obtain from that forage. For example, an increase in 1 percentage unit NDFD results in 0.37 pound (lb) increase in forage dry matter intake per day. Oba and Allen also reported that a 1 percentage unit increase for forage NDF digestibility resulted in 0.37 pound per day (lb/d) increase in DM intake and a 0.55 lb/d increase in 4 percent FCM yield. Jung et al. reported that when in vitro NDFD of corn silage increased by one unit, dairy cows ate 0.26 lb/d more DM and produced 0.31 lb/d more than 3.5 percent FCM.

Cows fed forages with greater NDFD are able to eat more and obtain more total energy from the forages. This results from a faster emptying of the rumen, which reduces distension and allows for even greater feed intake. As a result, energy requirements can be fulfilled with less grain required in the diet.

Corn allocation
High NDFD alfalfa and corn grain should be designated for animals that are more efficient in converting feed into milk (early lactation cows). Always remember to pay close attention to the ration particle size, to make sure there’s enough effective fiber. Check for loose, light colored manure and off feed, changes in feeding patterns and increased incidence of lameness.

Low NDFD alfalfa, on the other hand, may not be able to fulfill the energy requirements of cows’ high genetic potential. This is when allocating the right forage to the right cattle category becomes critical. If the forage at hand is of low quality/digestibility it should be given to animals that have lower requirements.

One point to remember is that high grain supplementation in diets that contain forages of low NDFD will result in a substitution effect. High grain concentration shifts rumen bacteria populations toward those that are more efficient in fermenting starch. This drops the rumen pH and further decreases fiber digestibility.

Feed efficiency
Feed efficiency, measured by the pounds of milk produced per pound of dry matter consumed, is an issue when you are deciding whether or not to remove high-priced corn from the diet.

Normal “target” values for feed efficiency vary, depending on the stage of lactation. As a herd average it should be between 1.3 and 1.5. Although values above 1.5 usually indicate higher efficiency and profitability, remember that in early lactation high efficiency is usually attained at the expense of body reserves.

When feed efficiency is under 1.3, cows are either eating too much, milk production has dropped or other management factors have changed.

Among the factors that affect feed efficiency are days in milk, age or lactation number, pregnancy requirements, bodyweight gain, diet digestibility, rumen fermentation enhancers, excessive heat or cold stress, feed additives and the use of BST.

Forages play the biggest role in affecting feed efficiency. Forages that are low in NDFD will have a negative impact whereas the opposite will be true for those with high NDFD.

One thing to watch for when feeding high-NDFD forages is to make sure they provide adequate effective fiber. Effective fiber and an adequate rumen mat formation are essential in maintaining proper rumen function. Digestibility and rate of passage “pull” in opposite directions. When there’s insufficient effective fiber (or decreased particle size) cud chewing is reduced, which results in less saliva being produced, a drop in rumen pH and reduced NDF digestibility. The advantage of feeding high-NDFD forages might be negated in the absence of adequate particle size and a shortage of relatively coarse, less digestible roughage that stimulates adequate rumination.

Is producing more milk the answer to high-priced corn?
An example of a basic ration for a 1,400-pound lactating cow producing 80 pounds of 3.5 percent fat is shown in Table 1. Forage-to-concentrate ratio is very close to 50-to-50. For the forage fraction, alfalfa and corn silage are included at a similar ratio. Corn grain represents 31 percent of the total ration on a DM basis. According to NRC estimations, total starch is right at 36.7 percent and nonfibrous carbohydrates (NFC) at 43.5 percent.

For every $1 increase in the price of a bushel of corn, there’s roughly a 33-cent increase in the cost of feeding each cow per day. When milk is at approximately $13 per hundredweight (cwt), every $1 increment in corn price is comparable to a reduction in the gross income of 2.5 pounds of milk.

Can you reduce the corn in the diet and still maintain acceptable production performance?

It is obvious that this diet containing 43.5 percent is “pushing the limit,” and you certainly have to be looking very closely at the physical effective fiber in order to avoid digestive upsets. It has been demonstrated that NFC concentration greater than 45 percent results in reduced milk yield.

On the other end of the spectrum, Iladdad and Grant evaluated the digestion of NDF from alfalfa or corn silage at low or high rumen pH, which was representative of cows that consumed a diet either deficient or adequate in effective fiber. They found that the optimum NFC-to-NDF ration to maximize NDF digestion varied for the two forages.

For alfalfa at the higher pH, NDF digestion was greatest between 30 and 40 percent NFC; but at the lower pH, 35 percent NFC maximized digestion. In the case of corn silage, NDF digestion was greatest at 30 percent NFC regardless of rumen pH. The authors concluded that the optimal NFC content was a function of the pH in the rumen, which is in turn affected by the effective fiber in the diet.

Summary
The search for renewable fuels has spurred the growth of ethanol plants across the U.S. and has increased the demand for corn grain. Prices for corn grain have increased to a point where feed costs will reduce income.

Re-examine diet composition regularly. Forages of higher NDFD and alternative co-product feeds that provide fermentable fiber will continue to be critical components of lactating cow diets. Lactating cow diets need to be balanced for optimum nonfibrous carbohydrate concentration. Pay attention to the effectiveness of the fiber in the ration. PD

References omitted but are available upon request at

—Excerpts from 3rd Annual I-29 Dairy Conference Proceedings

Alvaro Garcia, Kenneth Kalscheur, Arnold Hippen, Dairy Science Department; and Rebecca Schafer, Extension Educator, South Dakota State University

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