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0507 PD: Growing forages for quantity and quality

David B. Fischer Published on 09 May 2007

Forages have always been an important source of nutrients to the dairy cow. Producing high-quality forages can increase dairy efficiency and help reduce the feed costs associated with purchasing added supplements and concentrates. In addition, with the constant influx of new technology and innovations, forage management has become more sophisticated and provides a greater economic significance to dairy herd profitability.

Some forage growers suggest the goal of a well-managed forage production system is to produce maximum yields with maximum feed quality. While that may sound ideal, it is important to recognize it is not possible to achieve both maximum quantity and maximum quality. In order to reach maximum tonnage, we will lose quality to the maturity of the crop. Likewise, to achieve maximum quality we lose tonnage because we harvest a crop that is too immature. Therefore, the goal should be to optimize forage quantity and quality by careful selection of seed varieties, proper soil fertility, sound pest management and timely planting and harvesting.

Producing high quantity and quality alfalfa is largely dependent on harvesting at the optimum maturity. Alfalfa producers face several challenges in deciding when is the optimum time to begin harvesting the first cutting. It is well documented that alfalfa nutrient quality decreases as the plant matures from the bud stage to full flower. At the same time, the pounds of plant material harvested per acre increases as the plant matures. Thus, the optimum harvest date is the compromise between the feed quality and the feed quantity produced.

The Predictive Equation for Alfalfa Quality (PEAQ) is an excellent tool to help determine the first harvest date in the spring. PEAQ is an in-field predictor of forage quality by monitoring plant height and maturity. The plant height and maturity provides a close estimate of the Relative Feed Value (RFV) in the field. By determining the RFV of standing alfalfa, producers can more accurately gauge when to begin the first-crop harvest schedule.

First-cutting alfalfa needs to be harvested as soon as the RFV in the field reaches 170 in order to achieve high quality and to set-up the cutting schedule for the rest of the growing season. Subsequent cuttings should be taken every 26 to 30 days. Keep in mind the PEAQ analysis in the field does not include harvesting and storing losses. Various research trials have shown field and storage losses account for 15 to 20 points of RFV.

Therefore, in order to strive for premium quality alfalfa of 150 RFV, it would be necessary to harvest the first cutting when the PEAQ hits 170 RFV. While the RFV index is recommended to determine the PEAQ stage, the Relative Forage Quality (RFQ) is the preferred index for balancing the dairy cow ration.

Relative forage quality is based on in vitro neutral detergent fiber digestibility (NDFD) and summative equations. RFQ provides a better linkage between the forage quality and the actual cow response because it is a direct measure of the forage fiber degradation, and it can more accurately predict what goes on in the cow’s digestive system. RFQ will have a similar mean range as RFV. However, when evaluating purchasing or feeding forages based on RFQ and RFV, always use the RFQ index. The RFQ equation is not used in evaluating corn silage due to the starch fraction.

Producing high quantity and quality corn silage is dependent on hybrid selection, plant population, harvest maturity and harvest and storage management. Plant population can impact dry matter (DM) yield per acre. It is suggested plant populations for corn silage be increased by 10 to 15 percent over what is recommended for grain production. Corn silage hybrid selection should be made on the quantity and quality of corn silage produced.

Since feeding high-quality forages can improve your profits by reducing your purchased feed cost and improving herd performance, it is absolutely necessary and highly recommended to have your stored forages tested for nutrient content. This will provide more accuracy when balancing the diet for your dairy herd.

A forage test report can be a bit perplexing when you are looking at 20 to 30 lines of information, and the common question is “What do these numbers mean, and how does my forage compare?” The following is a list of some of the nutrient analysis components and suggested goals for corn silage tests.

Understanding corn silage forage test results

The following values are based on 100 percent DM to standardize the laboratory values and the suggested goals are for high-quality corn silage fed to lactating dairy cows.

•Moisture – 65 to 70 percent is suggested goal (68 to 70 percent if stored in bags or bunker; 65 to 67 percent if stored in an upright silo)

•Crude protein – includes all forms of protein and will range from 6 to 10 percent; the higher the number the better. Most corn silages will run about 7.5 to 8.5 percent.

•Soluble protein – a measure of what percent of the crude protein will degrade rapidly in the rumen; the number ranges from 20 to 40 percent. A mid-range number is best.

•Acid detergent fiber (ADF) – measures the cellulose and lignin portion. These percentages will vary depending on plant maturity, variety, etc. Range for corn silage ADF is 25 to 30 percent. In all forages, as fiber levels go up, energy value goes down, so the lower the fiber numbers the more energy is available for the cow; strive for a goal of 25 to 28 percent ADF.

•Neutral detergent fiber (NDF) – measures total cell wall and is influenced by maturity, variety differences, etc. NDF will range from 30 to 60 percent. As NDF percent increases the feed intake of the forage will decrease. A lower NDF is better with a goal of less than 45 percent NDF.

•Acid detergent insoluble nitrogen (ADIN) – measures “heat-damaged” or bound protein causing the crude protein to be tied up and not available to the cow. Should be less than 15 percent of total crude protein; the lower the number the better. If it is greater than 15 percent of the total CP, then use the adjusted crude protein number to balance the ration.

•Lignin – a very important number which is the nondigestible portion of the fiber. This ranges from 1.5 to 6.0 percent. The lower the lignin the better with a goal of 3.0 to 3.5 percent.

•Starch – indicator of grain content in corn silage and will range from 25 to 35 percent. The higher the amount of starch the better because it is a major energy source for the cow. A goal of 30 percent is suggested, realizing varieties can play a major role.

•Fat or ether extract – a vegetable fat (oil) content which is an excellent source of energy to the cow. Contents will range from 1 to 4 percent with a goal of 3 percent.

•Neutral detergent fiber digestibility – 30 hour. (NDFD-30) or cell wall digestibility (CWD) – an excellent in vitro test to determine the NDF digestibility (NDFD), as a percent of total NDF. In vitro means the feed is digested in rumen fluids (simulating a rumen) in the laboratory. This is a good indicator as to what the animal will actually digest of the forage in the “real world.” The NDFD-30 will range from 40 to 50 percent; the higher the better.

•NDFD-48 – used by some labs, the same procedure as NDFD-30 with the exception that the feed is in the simulated rumen for a 48-hour duration. The range for NDFD-48 can be 50 to 60 percent; the higher the better. Be careful not to compare the 30-hour with 48-hour because we will see higher NDFD in the 48-hour test.

•Other values – there are a number of other lab tests conducted to determine mineral content, pH content and other detailed fermentation analysis. In addition to the lab tests, there are several equations used to calculate the energy values for corn silage.

•Net energy lactation (NEL) is the more commonly expressed energy value used to balance rations. This calculated value will range from 0.72 to 0.78 mcal per pound; the higher the better.  PD

References omitted but are available upon request at

—From University of Illinois Extension website

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