PASTURE QUANTITY AND QUALITY

Lawrence D. Muller

Pennsylvania State Universitya

Pasture quantity and quality are the two most important factors in maximizing the amount of nutrients obtained from pasture. However, questions arise as to what is high quality pasture and how we can develop and maintain a high quality sward in abundant quantity.

Just like harvested forages, the nutritional quality of pastures is related to the maturity of the forage when harvested. Dairy producers strive to achieve legume forage with 20-23% crude protein (CP), 26-30% acid detergent fiber (ADF), 38-42% neutral detergent fiber (NDF), and a net energy for lactation (NEL) of 0.60 – 0.68 Mcal/NE/lb when harvested as stored forage.

With GOOD grazing management, grasses harvested by cows should be in a vegetative state and an approximate height 8 to 10 inches, depending on the type of grass. Grasses harvested as hay or silage are typically more mature than when harvested as pasture, thus pasture will be of higher quality than stored forages. Likewise, legumes such as clover or alfalfa are usually grazed at an earlier stage of growth than when harvested as stored forage. Therefore, with excellent grazing management we should expect to have higher quality forage when harvested as pasture than when harvested as stored forage. However, pasture quality will depend on many factors, including geographic location, environmental conditions (temperature, humidity, precipitation), types of grass and/or legume, and grazing management.

Seasonal Forage Growth and Quality Table 1 shows the average nutrient composition for cool season grass pastures. These are

average values and should be used as a guide. Forage testing and monitoring of nutrient composition are needed to more closely monitor the supplemental feeding program. In general, pastures containing some legumes are higher in nutrient value and will likely be consumed in higher amounts than only grass pastures. The type of grass and the inclusion of legumes will influence pasture composition. The seasonal effects on nutrient composition are illustrated with columns titled spring and summer. For most grasses and grass/legume mixtures, the protein and energy content are higher in spring and fall and lower during the summer. These fluctuations in nutrient content are closely correlated with the annual growth cycle of the forage. In appendix Table 1 is a more complete nutrient composition for several different grasses and legumes.

aDepartment of Dairy and Animal Science (lmuller@psu.edu)

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Table 1. Average nutrient composition for cool season grass pasture and legumes over a grazing season.a

Predominately grass (cool season) Grass with legumes

Nutrient Spring Summer Spring Summer

Crude protein (CP), % DM 21-25 18-22 22-26 20-24

RUPb, % of CP 20-25 25-30 20-25 25-30

RDPc, % of CP 75-80 70-75 75-80 70-75

ADF, % DM 24-28 28-34 21-25 25-30

NDF, % DM 40-45 48-55 32-37 38-43

NE, Mcal/ 0.7 1-0.76 0.66-0.72 0.74-0.80 0.70-0.74

Non-fiber carbohydrate (NFC)d, % DM 15-20 12-15 18-24 15-20

Fat, % DM 3-4 3-4 3-4 3-4

Ash, % DM 7-9 7-9 8-9 8-9

Ca, % DM .50 - .75 .50 - .75 1.1-1.3 1.1-1.3

P, % DM .30 - .35 .30 - .35 .30-.35 .30-.35

Mg, % DM .15 - .20 .15 - .20 .18-.24 .18-.24

K, % DM 2.0 - 3.0 2.0 - 3.0 2.5 – 3.5 2.5-3.5

aSummarized from Fales et al., 1995 and five other studies in the Northeast USA. bRumen undegradable protein cRumen degradable protein grazing and feeding management decisions. dNFC = 100 – (CP + NDF + Fat + Ash)

In Table 2 is shown the change in nutrient composition of a mixed mostly grass pasture in the Northeast USA throughout the grazing season. During periods of peak growth (spring and fall), CP, RDP, NFC, and NEL are higher, while NDF is lower. The reverse happens during the summer months, when growth rates are lower, fiber increases, and nutritional value declines.

Table 2. Variation in nutrient composition of a mixed mostly grass pasture throughout the grazing season (adapted from Rayburn, 1991). May June July Aug Sept Oct CP, % of DM 24 22 20 20 22 24 RDP, % of CP 74 73 72 71 71 74 NDF, % of DM 47 49 51 52 48 45 NFC, % of DM 16 15 14 13 15 16 NEL, Mcal/lb 0.73 0.70 0.66 0.66 0.72 0.75

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The nutrient composition of an orchardgrass pasture during a grazing season from a Penn State study is shown in Figure 1. These results are from well-managed pastures that were grazed at a stocking rate of 1.3 cows per acre and had nine grazing rotations during a six month grazing season. vegetative state and should be representative of most intensively-managed pastures. Crude protein remained greater than 20% for the entire grazing season. Fiber increased and in vitro dry matter digestibility (IVDMD) decreased during the summer. These results suggest the analysis of pasture perhaps three times per year to coincide with changing seasons may be adequate when pasture availability is not limiting.

feeding programs with pasture. The variability in nutritional composition throughout the grazing season or BETWEEN grazing years emphasizes the need for some re-formulation of the dairy ration throughout the grazing season. nutritional quality changes. usually taken when a change in bunkers occurs, when the field harvested changes within a silo, or when a new source of forage is fed. The same applies for pastures.

to lactating dairy cows. However, at other times of year, perhaps only concentrate, mineral and/or a rumen undegradable protein source is all that is necessary to maintain animal health and productivity. One of the most important concepts with grazing is to frequently monitor forage quality, especially the first few years, and to be flexible and be prepared for change, depending on weather patterns, forage growth, and changing nutritional composition.

0

10

20

30

40

50

60

70

80

CP NDF IVDMD

%of

DM

Figure 1. Nutrient composition of orchardgrass-based pasture during six month grazing with 9 rotations per paddock.

Quality remained high with this well-managed pasture where grass was grazed in the

The values presented in Tables 1 and 2, and Figure 1 can be important when formulating

In addition, regular forage testing is important as the When formulating rations with stored forages, forage tests are

During periods of summer heat and drought, additional forages may need to be provided

Grazing Cycle

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If cows are moving to pastures that have a different forage composition, forage testing is recommended. Keep in mind that forage tests are always subject to errors and good judgment is necessary when interpreting results and developing feeding strategies.

Summary:

Well-managed pastures, regardless of the plant species, can be high in nutrient quality and often exceed the nutrient composition of high quality stored forages. Good grazing management is essential to maintaining quality pasture. Changes in season trigger changes in rate of plant growth and subsequent changes in nutrient composition. The continual changing of pasture quantity and quality during the grazing season provides challenges to dairy producers using a grazing system. Use of available information about forage quality and nutrition can lead to sound grazing and feeding management decisions.

Keys to High Quality Forage Production

• Know when the forage canopy is ready to be grazed • Know how much residual to leave before moving to another paddock • Know how long it takes to use the canopy to the desired residual • Use a stocking density which allows quick removal of forage and uniform distribution of

excreta

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Reference Table 1. Average nutrient composition of typical high quality pastures (dm basis). Cool Season

Grass, Spring

Cool Season Grass,

Summer

Cool Season Grass,

Fall

MMG1

Pasture, Spring

MMG1

Pasture, Summer

MMG1

Pasture, Fall

LegumePasture, Spring

LegumePasture, Summer

DM, % CP, % RUP, % of CP Sol.P,% of CP ADF, % NDF, % NEL, Mcal/lb NSC/NFC, % Ca, % P, % Mg, % K, % S, % Mn, ppm Cu, ppm Zn, ppm Fe, ppm Se, ppm Vit. A, IU/lb Vit. D, IU/lb Vit. E, IU/lb Fat, % Ash, %

20 20-22 20 40 26-30 43-47 .72-.75 15-20 .50 .30 .16 3 .22 70 8 28 146 0.04 40,000

250 3 10

--

20 18-20 30 35 30-34 48-54 .68-.72 14-18 .50 .30 .18 3 .22 70 8 28 146 0.04 40,000

250 3 10

--

20 20-22 25 40 24-28 42-46 .71-.74 17-21 .50 .30 0.20 3 .22 70 8 28 146 0.04 40,000

250 4 10

--

20 21-23 20 40 25-29 41-45 .73-.77 16-21 .75 .28 .16 3 .22 70 9 28 205 0.04 40,000

250 4 11

--

20 20-22 30 35 29-33 45-50 .68-.72 13-18 .75 .28 .18 3 .22 70 9 28 205 0.04 40,000

250 4 11

--

20 22-24 25 40 24-28 40-44 .73-.77 16-20 .75 .30 .21 3 .22 70 9 28 205 0.04 40,000

250 4 11

--

20 21-25 15 40 26-30 37-41 .73-.76 16-20 1.3 .30 .22 3.3 .22 56 9 30 194 0.04 40,000

250 4.30 11

--

20 21-25 20 35 28-32 39-43 .68-.72 15-19 1.3 .30 .22 3.3 .22 56 9 30 194 0.04 40,000

250 4.30 11

--

1MMG = Mixed Mostly Grass.

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Reference Table 1 continued. Average nutrient composition of typical high quality pastures (dm basis). LegumePasture,

Fall MML1 Pasture,

Spring MML1 Pasture,

Summer MML1 Pasture,

Fall Sor-Sud2

Pasture, 30 inches

Sor-Sud2

Pasture, 40 inches

Kale Tops, Brassicas

DM, % CP, % RUP, % of CP Sol.P, % of CP ADF, % NDF, % NEL, Mcal/lb NSC/NFC, % Ca, % P, % Mg, % K, % S, % Mn, ppm Cu, ppm Zn, ppm Fe, ppm Se, ppm Vit. A, IU/lb Vit. D, IU/lb Vit. E, IU/lb Fat, % Ash, %

20 27 20 40-45 25-29 33-38 .72-.75 16-20 1.3 .30 .26 3.31 0.24 56 9 30 194 0.04 40,000

250 4.30 13

--

20 22-24 20 40 26-30 35-39 .73-.77 15-20 1.0 .30 .16 3.3 .20 60 9 28 186 0.04 40,000

250.00 4 11

--

20 22-24 25 35 28-32 40-45 .68-.72 15-20 1.0 .30 .22 3 .20 60 9 28 186 0.04 40,000

250 4 11

--

20 23-25 20 40 24-28 36-40 .72-.76 15-20 1.0 0.30 .23 3 .20 60 9 28 186 0.04 40,000

250 4 13

--

20 15 36 35 34-38 56-60 .63-.67 13-16 .55 0.27 .28 2.1 0.1 68 9 34 267 0.03 36,000

216 3 9.5

--

22 13 38 32 38-42 60-65 .60-.64 11-14 0.50 0.30 0.30 2.60 0.12 68 9 34 268 0.03 34,000

204 3.10 9.5

--

12 16-18 37 35 28-32 38-42 .74-.78 26-30 1.61 0.34 0.30 2.78 0.29 52 17 36 93 0.03

4 10

-- -- --

1MML = Mixed Mostly Legume. 2Sor-Sud = Sorghum-Sudangrass.

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