Using a Forage Test to Identify Improvements
in Forage Management

Edward B. Rayburn, Ph.D., Extension Forage Agronomist
1998

A forage test can be used to detect forage management problems as well as to balance an animal's ration. This fact sheet outlines variables reported in a forage test and forage management options that can be used to improve forage quality.

The first question to be addressed is, do I need to change my management? The forage quality needed is dependent on the animal's nutritional requirement, the value of the forage, and the cost of energy and protein supplements. In general it is cheaper to grow good- quality forage than to buy supplements for poor- quality forage. Table 1 lists the energy and protein requirements for different classes of cattle and the forage ADF (average± range) associated with that level of energy. In general, it is most cost effective to provide all or most of the animals' nutritional needs from quality forage.

Moisture (Dry Matter) is an indication of how well the forage was dried before storage. Hay crops should be baled when the moisture is less than 20% (dry matter greater than 80%). Haylage should be made when the forage moisture is 40-50% (dry matter 50-60%). Most hays will dry to 10-15% moisture (85-90% dry matter) during storage though some round bales can be higher in moisture when wrapped for haylage or when stored outside. Ensure that you allow hay to dry adequately before baling.

Acid Detergent Fiber (ADF) is the best measure of fiber for forage. If ADF is high, digestibility will be low. A level of total ration ADF above 21% is needed by dairy cattle to maintain butterfat production. Forage crops increase in ADF as they grow and mature. Reduce the ADF in hay by harvesting at an earlier growth stage. When managing for ADF levels that are lower than needed by the livestock, forage yield may be reduced due to harvesting too early. Balance between ADF content and yield .

Table 1. The total digestible nutrient (TDN) and crude protein (CP) requirement for different cattle classes and the approximate forage acid detergent fiber (ADF, average ± range) content which will supply the indicated TDN.

Production Status

TDN

CP

ADF

------------ % ------------

Growing steer

60-68

10-11

34 +5

Dry cow

50

7

42 +5

Last 3rd gestation

52-54

8

40 +5

Lactating beef cow

   average

55-56

9

39 +5

   above average

63-64

11-12

34 +5

   heifer

62-64

10-11

34 +5

Lactating dairy cow

   50-70 lb milk/day1

68-70

15-16

27 +5

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1 At milk production levels over 50 lb milk/day grain supplementation will be needed.

Neutral Detergent Fiber (NDF) is the best measure of forage dry matter intake by livestock. The lower the NDF content the higher the intake. Legumes are lower in NDF than grasses at the same growth stage but both increase in NDF as they grow and mature. If there is the need for animals to eat more forage, manage the stand for a lower NDF content. This can be done by harvesting at an earlier growth stage or inter-seeding legumes.

Crude Protein (CP) is a measure of the nitrogen in the forage. The CP is used by rumen bacteria in digesting forage and concentrates in the diet. The bacteria digest fiber and nonstructural carbohydrates in the ration, releasing volatile fatty acids that ruminants use for energy. Ruminants also digest the bacteria for energy and high quality protein as they pass out of the rumen. The CP content of forage can be increased by adding legumes to the stand, by harvesting the forage at an earlier growth stage, or (to a small extent) by using higher rates of nitrogen fertilizer.

Digestible Energy (DE) of forage is calculated from the measured fiber content. Several different energy systems are used in formulating livestock rations. The energy systems used in the United States are summarized in Table 2 using equivalent values. Table 2 can be used for converting the feeding value of forage or grain supplement from one energy system to another. Horses digest forages less efficiently than ruminants. To estimate an energy value for horses, multiply the energy values in Table 1 by 0.80. To increase the digestible energy in a forage, manage the stand to decrease the forage ADF content. Also, to increase digestible energy intake decrease the forage NDF by adding legumes to the stand. Livestock will eat more grass-legume forage than straight grass, be it hay or pasture. Forage containing 25-30% legumes will allow yearling cattle to grow 0.25-0.33 lb/day faster than nitrogen fertilized grass and dairy cattle will produce 6-10 lb/day more milk at the same level of grain feeding. For high producing dairy cattle grain will often be needed for supplemental energy since cool season grasses and legumes are often short of energy compared to protein.

Table 2. Equivalent values for total digestible nutrients (TDN), digestible energy (DE), metabolizable energy (ME), net energy maintenance (NEM), net energy gain (NEG), and net energy lactation (NEL) (NRC 1984 and 1988).

TDN

DE

ME

NEM

NEG

NEL

%

------------------- Mcal / lb -----------------

45

0.90

0.74

0.36

0.11

0.45

50

1.00

0.82

0.44

0.19

0.50

55

1.10

0.90

0.52

0.26

0.56

60

1.20

0.99

0.60

0.33

0.61

65

1.30

1.07

0.67

0.40

0.67

70

1.40

1.15

0.74

0.47

0.73

75

1.50

1.23

0.81

0.53

0.78

80

1.60

1.31

0.88

0.59

0.84

85

1.70

1.40

0.95

0.65

0.89

90

1.80

1.48

1.02

0.70

0.95

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Forage quality is mainly determined by harvest management and legume content. If the quality of pasture and hay is equal to or greater than that needed by the livestock being fed, then there is no need to change management. However if the forage quality is lower than needed it can often be improved by earlier harvest or by including legumes in the stand.

References:

  1. National Research Council. 1989. Nutrient Requirements of Horses. National Academy Press, 2101 Constitution Ave., NW, Washington, DC 20419.
  2. National Research Council. 1988. Nutrient Requirements of Dairy Cattle. National Academy Press, 2101 Constitution Ave., NW, Washington, DC 20418.
  3. National Research Council. 1984. Nutrient Requirements of Beef Cattle. National Academy Press, 2101 Constitution Ave., NW, Washington, DC 20418.
  4. Rayburn, E.B. 1994. Forage Quality of Intensive Rotationally Grazed Pastures. Extension Memo, Oct. 1994. West Virginia University Extension Service, PO Box 6108, Morgantown, WV 26506-6108.

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Programs and activities offered by the West Virginia University Extension Service are available to all persons without regard to race, color, sex, disability, religion, age, veteran status, sexual orientation, or national origin. Issued in furtherance of Cooperative Extension Work, Acts of Congress of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Lawrence Cote, Director, Cooperative Extension Service, West Virginia University