The main goal of dairy nutrition is to match the nutrient requirements of the cows with nutrients provided by feed ingredients. However, in addition, a quality dairy cow ration should optimize cow health and production, maximize forage feeding, minimize the excretion of nutrients and be cost-efficient. This [article] will outline current trends in feeding dairy cows and highlight some of the challenges we may face in the future when formulating dairy cow rations.

Forages
•Increased use of corn silage and less alfalfa in dairy cow diets
In the last 10 years, states that ranked within the top six in milk production (California, Wisconsin, New York, Pennsylvania, Idaho and Minnesota) increased corn silage production from 120 percent to over 200 percent. In contrast, alfalfa production has either remained steady or has slightly declined.

Increased production and use of corn silage is most likely influenced by a number of factors. For example, corn silage is harvested once per season rather than three or more cuttings for alfalfa, which simplifies harvesting and storage. With a limited land base, corn silage also allows producers to harvest more tons of dry matter and TDN per acre than with legumes and grasses. Harvesting quality corn silage is less difficult than alfalfa, resulting in a more consistent feed ingredient. In contrast to alfalfa or grasses, corn silage contains both forage and grain, and therefore provides a good source of fiber along with starch, which decreases the amount of additional grain required in the diet.

•Forage fiber sources
Dairy cows need a minimum amount of longer fiber particles from forage to maintain rumen health. Even though it has a low nutritive value, there has been an increased use of straw in diets to provide a source of longer ‘effective fiber.’ In the future, we may see more tailoring of hay species (legumes and grasses) and quality to fit feeding method.

For farms feeding long-stemmed baled hay, soft-stemmed high quality will be the desired hay forage; whereas if the hay is chopped for feeding, a lower quality may be preferred to effectively meet fiber requirements. However, in some rations where corn silage and co-products will be providing the energy in the diet, high-quality hay may not have an increased value over moderate-quality hay.

Corn
•Decreased availability of grain for use in dairy cow rations
Corn is increasingly being utilized for ethanol production. In 2000, the ethanol industry used approximately 600 million bushels of corn. This crop year, it is expected to reach 2.15 billion bushels and the projection for 2007 is 3.2 billion bushels. Currently, corn prices are at a 2.5-year high. If this trend continues, starch will be one of the scarcest and highest-priced nutrients in dairy rations and many dairy producers will be looking to alternative feeds as a replacement for corn.

High-producing cows need a certain level of starch (approximately 25 percent diet DM) for good microbial protein production, rumen function and milk yield. However, as corn prices have increased, prices for other grains that contain starch such as oats, barley and wheat have also increased.

One alternative to feeding corn grain is to feed more corn silage and fewer legumes and grass forages. Data from the University of Minnesota indicate feeding higher corn silage diets will allow dairy producers to feed decreasing corn diets with excellent performance. Early lactation cows were fed diets ranging from 31 to 50 percent corn silage (DM basis) and 28 to 0 percent corn (DM basis). Alfalfa hay was constant at 15 percent of ration DM.

All diets resulted in at least 90 pounds milk per day and cows receiving diets without any corn produced approximately 100 pounds milk per day. It is important to note, however, that cows were placed on their respective diet immediately after calving and as corn grain in the diet was decreased, additional fat was added to diets to achieve an equal energy level to the high corn diet.

Co-products
•Increased availability of co-products for use in dairy cow rations
The amount of co-products from the ethanol, biodiesel and the food industry will continue to increase. Many of these co-products make excellent livestock feed. For dairy, however, there are three limitations to feeding large quantities of co-products:

1. Starch
To get top milk production, dairy rations need to contain about 25 percent of the DM as starch. In both the ethanol and food industry, the starch is utilized in the production of their respective products. Most co-products are very low or devoid of starch.

2. Phosphorus
Most co-products from the ethanol or food industry are two to three times higher in phosphorus (P) content than corn. Feeding high amounts of these co-products increases the total P content in the ration well above animal requirements. This will result in increased excretion of P in the manure and potentially P loading of the soil.

3. Protein
Most co-products contain more than 20 percent crude protein (CP) or two to four times the CP content of corn. If co-products are used to replace feed ingredients in the ration low in CP (such as corn), it will be very difficult to formulate rations below 18 percent CP, especially if alfalfa is the major forage utilized in the ration. Feeding high protein rations results in more nitrogen excretion in urine and manure, which will make it more difficult to comply with odor and air quality standards and increases the risk of surface and groundwater contamination.

Distillers grains
As the ethanol industry continues to rapidly develop, one of the major co-products of interest in dairy cow diets is distillers grains (DG). The ethanol industry produces 245 pounds of distillers for every dairy cow in the United States. This is the result of 17 pounds of DG being produced from every bushel of corn utilized in ethanol production.

How much distillers grains can be included in lactating dairy cow rations?
In 2005, Kalcheur et al. conducted a meta-analysis of 24 studies in which wet or dried DG were fed to lactating dairy cows. Results showed diets with greater than 30 percent DG resulted in decreased intake, milk yield and milk protein percent. However, the data indicated DG can be fed up to 20 percent of the ration DM, about 10 to 12 pounds per cow per day as fed, in lactating dairy cow diets without negatively impacting production.

Things to consider when feeding distillers grains (DG)
Feeding high levels of DG (20 percent diet DM) may be possible in some dairy cow rations, but most producers stay at 10 percent of the ration or lower. Here are some things to watch out for and consider when feeding DG:

•The nutrient composition of wet and dried DG can be quite variable. If you are going to feed 10 percent or more of the ration as DG, know your source and nutrient quality guarantees.

•Wet DG in high corn silage or other fermented forage rations may result in rations being too wet, which could limit DM intake.

•DG and corn have similar energy values, but the energy in DG is from fat and in corn, it is from starch. Substituting DG for corn grain will lower starch levels in the ration and may decrease milk production.

•Fiber from distillers is not effective at promoting cud chewing or maintaining rumen function. Fiber from forage must be maintained in rations.

•High oil diets can depress milk fat test, especially with the use of Rumensin.

•Lysine levels in corn products are low and therefore lysine may be limiting in some DG diets.

•The high P content of DG may affect crop nutrient management plans.

Economics of DG replacing corn and soybean meal in lactating dairy cow rations
The CP (28 percent) and net energy content (0.80 Mcal per pound) on an as-fed basis of dry distillers grains with solubles (DDGS) is very similar to a 50-to-50 mix of corn and 47 percent protein soybean meal. Thus, from a protein and energy basis, adding 1 pound of DDGS into a ration should replace 0.5 pound of corn and 0.5 pound of soybean meal.

Future feeding challenges

Co-product use
Increasing demand to produce energy and other products from feedstuffs will increase the availability of co-products. Diets will become increasingly diverse, depending on co-products available in a specific region. Nutritionists and dairy producers will need to better understand the feeding value of these co-products and match forage production or procurement with co-product usage.

Nutrient excretion
As farms become larger, utilizing nutrients in the manure in a fiscal and environmental manner will continue to be a challenge. Nutritionists will be required to balance diets that meet animal requirements, but minimize nutrient excretions.

Economical starch sources
Starch may become one of the highest-priced ingredients in dairy cow diets. Finding economical starch sources or optimizing production in low-starch diets may be one of our feeding challenges.

Biodiesel demand
Currently most of the discussion about alternative energy sources focuses on ethanol. However, it is estimated the United States will be producing over one billion gallons of biodiesel per year within the next five years. Estimates are that over half of this will be made from animal fat. This may increase the cost of fat for use in dairy cow diets.

Conclusion
The increased demand for land to produce energy and other products will affect how we feed our cows in the future. Availability of various co-products will increase and prices for grains may increase. Nutritionists and dairy producers should monitor these trends and develop feeding strategies accordingly. PD

References omitted but are available upon request.

—From 2nd Annual I-29 Dairy Conference Proceedings