Cooperative Extension University of Wisconsin-Extension

Issues in Agriculture

Extension Responds: Drought

Feeding Strategies When Forage Supplies Are Short

By. R. D. Shaver, Professor and Extension Dairy Nutritionist, University of Wisconsin-Madison/Extension
August 21,2003

Introduction

Low carry-over forage inventories, alfalfa winter-kill, and light first crop yields along with late-summer drought conditions in parts of Wisconsin have resulted in many questions about strategies for coping with short forage supplies for cattle. A small negative differential between hay-crop forage inventory and needs may simply mean increasing the proportion of corn silage in diets for replacement heifers, milking cows, or both, and minimizing feeding losses and refusals. A moderate to large negative differential between hay-crop forage inventory and needs and/or a corn silage short-fall may require more drastic measures -- feeding lower forage diets, purchasing and feeding higher amounts of high-fiber byproducts, purchasing and feeding higher amounts of hay, or feeding straw, depending on the severity of the situation. Diet changes intended to stretch forage supplies should be done under the supervision of a ration consultant. Forage quality will likely be highly variable because of high crop variability, so forage testing is extremely important to enable proper supplementation strategies by ration consultants.

Fibrous and Non-Fibrous Carbohydrate Guidelines

Unlike other nutrients, such as protein and calcium, where requirements are provided in grams per cow per day for specific body weight and milk production levels, fiber “requirements” are merely minimum guidelines aimed at maintaining normal ruminal pH, fiber digestion and milk fat test and preventing digestive disorders. NRC (2001) guidelines for minimum NDF from forage, minimum total diet NDF, and maximum diet NFC are presented in Table 1. Remember that these are fiber minimums and NFC maximums, and not recommended formulation targets for all situations.

Table 1 applies to diets containing ground corn as the primary starch source fed as TMR of adequate particle size, and assumes good feed delivery and bunk management practices. Greater formulation safety margins (i.e higher NDF from forage and total NDF minimums and lower NFC maximums) should be used in herds without TMR feeding or with inadequate TMR particle size, highly rumen fermentable starch sources (i.e. steam-flaked corn or high moisture corn versus dry corn), and (or) poor feed delivery and bunk management practices (Refer to Table 2). Adequate TMR particle size means having at least 8 to 10 percent retained on the top screen of the Penn State-Nasco shaker box with less than 50 percent found on the bottom pan (as-fed basis; two-screen plus pan system). If particles on the top screen come primarily from dry hay or straw rather than silage, then a TMR with 6 percent (as-fed basis) residing on the top screen may be adequate.

Low forage inventories and high relative costs of fiber and other nutrients from purchased forages versus purchased high-fiber byproducts may create the need or desire to feed minimum forage diets. Diets with less than 19 percent NDF from forage should contain high-fiber byproducts to increase total diet NDF and reduce diet NFC (Refer to Table 1). Selected high-fiber byproducts and their respective NDF and NFC concentrations are presented in Table 3 for comparison with common forages and grains. In general, replacing grains with high-fiber byproducts has the effect of raising total diet NDF and reducing diet NFC. This practice is positive in low forage diets, as it aids in meeting the total diet NDF and NFC recommendations. The NDF in high-fiber byproducts is not as effective as the NDF from forage for maintaining normal milk fat test (Armentano and Pereira, 1997). The exception to this is whole cottonseed where the NDF effectiveness factor relative to forage NDF is near 100% (Clark and Armentano, 1993). This is one of the main reasons why whole cottonseed has become such a common feed ingredient in low forage diets. The 15 percent NDF from forage row in Table 1 is not recommended, because a depression in milk fat test would be expected. Assuming an average NDF concentration for dietary forages of 45 percent, diet formulation for 19 percent or 16 percent NDF from forage would result in diets containing 42 percent or 35 percent forage (DM basis), respectively (Refer to Table 4). Again, greater formulation safety margins (i.e higher NDF from forage and total NDF minimums and lower NFC maximums) should be used in herds without TMR feeding or with inadequate TMR particle size, highly rumen fermentable starch sources (i.e. steam-flaked corn or high moisture corn versus dry corn), and (or) poor feed delivery and bunk management practices (Refer to Table 2).

There are numerous errors in feed delivery and bunk management that can occur on commercial dairies (i.e. errors in feed sampling and analyses, errors in ingredient DM adjustments, failure to evaluate forage and TMR particle size, failure to evaluate grain moisture content and degree of processing, errors in ingredient feeding rates, mixing errors including over-mixing that causes particle size reduction, and feed sorting). Close attention should be paid to proper feed delivery and bunk management practices, especially when implementing diet changes aimed at stretching forage supplies. Factors that may make TMR prone to sorting include: DM content and particle size of forage and mix, variation in bulk density of feed ingredients, large pieces of cobs and husks in the corn silage, amount and quality of hay added to mix, improper sequencing of ingredients into the mixer, frequency of feeding and push-up, availability of bunk space, and bunk access time. An on-farm evaluation of sorting should include particle size determination of TMR, bunk mix, and refusals. If sorting is determined to be a problem, then one or more of the following options may need to be considered: feeding smaller amounts of TMR more frequently, adding less hay to the mix, processing hay finer, using higher quality hay, using hay that is more pliable, processing corn silage, addition of water to dry TMR, and addition of a liquid feed supplement to TMR.

Presented in Table 5 are example calculations of forage replacement values for alternative roughage sources and high-fiber byproducts. The feeding 5 lb./cow/day DM from coarse-chopped hay can replace 5.5 to 7.0 lb./cow/day of haylage DM. In theory, coarse-chopped straw could replace up to 10.5 lb. of haylage DM. But, in practice straw is usually limited to 2 to 4 lb./cow/day for milking cows to formulate diets of sufficient energy density resulting in a potential haylage DM replacement of 4 to 8 lb./cow/day. Feeding 5 lb./cow/day DM from high-fiber byproducts replaces only 2.0/cow/day haylage DM on average, except for whole cottonseed and cottonseed hulls with haylage replacement values of 6 and 10 lb./cow/day DM, respectively, at 5 lb./cow/day DM feeding rates. High forage replacement with cottonseed hulls should coincide with the feeding of coarse-chopped dry hay to provide adequate rumen mat formation. Because of poor growing and harvest conditions for the 2002 cotton crop, whole cottonseed quality (moisture, mold, mycotoxins, and free fatty acids) and price need to be closely evaluated when deciding whether or not to feed whole cottonseed or how much to feed. Ration consultants and feed suppliers should be called upon to assist with evaluating the potential for using whole cottonseed to stretch forage supplies.

Suggested feeding limits for selected high-fiber byproducts are presented in Table 6 (Adapted from Howard, 1988). Actual amounts fed should be determined by formulation of diets for requirements and limits for nutrients, such as CP, RUP, RDP, NDF, NFC, fat and P, especially when multiple high-fiber byproducts are used in the same diet. For a detailed discussion of by-product feeds, the following internet publication is recommended: http://www.wisc.edu/dysci/uwex/nutritn/pubs/ByProducts/ByproductFeedstuffs.html . Break-even prices for byproduct feeds can be calculated using FEEDVAL4 (Howard and Shaver, 1993) with blood meal (rumen undegraded protein), urea (rumen degraded protein), shelled corn (energy), tallow (fat), dicalcium phosphate (phosphorus), and calcium carbonate (calcium) as referee feedstuffs. Break-even prices are not provided here, because actual break-even prices vary as prices of the referee feedstuffs change. These change from month to month, year to year, supplier to supplier, and location to location. Calculation of relevant breakeven prices is recommended. The FEEDVAL4 spreadsheet can be obtained at the following internet URL: http://www.wisc.edu/dysci/uwex/nutritn/spreadsheets/sprds.htm . Remember to input currently relevant prices for referee feeds into the spreadsheet so that the calculated breakeven prices from the spreadsheet are relevant.

References

Armentano, L. E., and M. Pereira. 1997. Measuring the effectiveness of fiber by animal response trials. J. Dairy Sci. 80:1416-1425.

Clark, P. W., and L. E. Armentano. 1993. Effectiveness of neutral detergent fiber in whole cottonseed and dried distillers grains compared with alfalfa haylage. J. Dairy Sci. 76:2644-2650.

Howard, W. T. 1988. Here are suggested limits for feed ingredients. Hoard's Dairyman. March 25, 1988. pg. 301.

Mertens, D. R. 2002. Measuring fiber and its effectiveness in ruminant diets. Page 40-66 in Proc. Plains Nutr. Cncl. Spring Conf. San Antonio, TX.

National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7 th rev. ed. Natl. Acad. Sci., Washington, DC.

 

Table 1. Recommended minimum concentrations (%of DM) of NDF from forage and total diet NDF and recommended maximum concentrations (%of DM) of NFC for diets containing ground corn as primary starch source fed as TMR of adequate particle size (NRC, 2001).

Minimum NDF from forage

Minimum NDF in Diet

Maximum NFC in diet 1

 19%

 25%

 44%

 18%

 27%

 42%

 17%

 29%

 40%

 16%

 31%

 38%

 15% 2

 33%

 36%

1 Non-fiber carbohydrate = 100 – (%NDF – NDFIP + % CP + %Fat + %ash).

2 Not recommended because of depression of milk fat test.

 

Table 2. Recommended minimum concentrations (% of DM) of NDF from forage and total diet NDF and recommended maximum concentrations (% of DM) of NFC for diets of lactating dairy cows fed in herds without TMR feeding or with inadequate TMR particle size, highly rumen fermentable starch sources (i.e. steam-flaked corn or high moisture corn versus dry corn), and (or) poor feed delivery and bunk management practices (adapted from NRC, 2001).

Minimum NDF from forage

Minimum NDF in Diet

Maximum NFC in diet 1

 19%

 --

 --

 18%

 --

 --

 --

 29%

 40%

--

 31%

 38%

 --

 33%

 36%

1 Non-fiber carbohydrate = 100 – (%NDF – NDFIP + % CP + %Fat + %ash).

Table 3. Tabular mean NDF and NFC concentrations (% of DM; NRC, 2001) for selected forages, grains, and high-fiber byproducts.

Ingredient

NDF%

NFC% 1

 Alfalfa

 35-50

 20-30

Grasses

50-65

10-20

Corn Silage

45-55

30-40

 

 

 

Shelled Corn

9.5

75.4

Ear Corn

21.5

64.3

 

 

 

Alfalfa Meal

41.6

28.8

Beet Pulp

45.8

35.8

Brewers Grains

47.4

13.9

Canola Meal

29.8

25.9

Citrus Pulp

24.2

56.8

Corn Gluten Feed

35.5

30.4

Cottonseed Hulls

85.0

3.5

Cottonseed Meal

30.8

19.0

Distillers Grains

38.8

16.3

Hominy

21.1

60.1

Linseed Meal

36.1

31.0

Malt Sprouts

47.0

23.2

Soybean Hulls

60.3

18.3

Sunflower Meal

40.3

27.7

Wheat Middlings

36.7

35.3

Whole Cottonseed

50.3

2.7

1 Non-fiber carbohydrate = 100 – (%NDF – NDFIP + % CP + %Fat + %ash).

Table 4. Calculated forage concentration in the diet to meet minimum NDF from forage guidelines with forage of varying NDF concentration (DM basis).

Minimum NDF from forage

40% NDF forage

45% NDF forage

50% NDF forage

 19%

 48% 1

 42%

 38%

 18%

 45%

 40%

 36%

 17%

 43%

 38%

 34%

 16%

 40%

 35%

 32%

1 Dietary forage concentration as % of DM.

Table 5. Example calculations of forage replacement values for alternative roughage sources and high-fiber byproducts.

 

Ingredient

NDF 1

% of DM

pef 2

% of NDF

peNDF 3

% of DM

Replaces

per lb. DM 4

Replaces

per 5 lb. DM

 Replaced Haylage

 

 

 

 

 

Medium Chop Length

45

85

38.3

--

--

 

 

 

 

 

 

Replacement Feeds

 

 

 

 

 

Coarse Chopped Straw

73.0

110

80.3

2.1

10.5 5

Coarse Chopped Grass Hay

55

95

52.3

1.4

7.0

Coarse Chopped Alfalfa Hay

45

90

40.5

1.1

5.5

Alfalfa Meal

41.6

40

16.6

0.4

2.0

Beet Pulp

45.8

30

13.7

0.4

2.0

Brewers Grains

47.4

40

19.0

0.5

2.5

Canola Meal

29.8

40

11.9

0.3

1.5

Citrus Pulp

24.2

30

7.3

0.2

1.0

Corn Gluten Feed

35.5

40

14.2

0.4

2.0

Cottonseed Hulls

85.0

90

76.5

2.0

10.0 6

Cottonseed Meal

30.8

40

12.3

0.3

1.5

Distillers Grains

38.8

40

15.5

0.4

2.0 7

Hominy

21.1

40

8.4

0.2

1.0

Linseed Meal

36.1

40

14.4

0.4

2.0

Malt Sprouts

47.0

40

18.8

0.5

2.5

Soybean Hulls

60.3

30

18.1

0.5

2.5

Sunflower Meal

40.3

40

16.1

0.4

2.0

Wheat Middlings

36.7

40

14.7

0.4

2.0

Whole Cottonseed

50.3

90

45.3

1.2

6.0 7

1 Adapted from NRC (2001).

2 Physical effectiveness factors (% of NDF) adapted from Mertens (2002).

3 Physically effective NDF (% of DM) calculated as NDF*(pef/100).

4 Replacment value of feeds per lb. of DM for example haylage calculated as peNDF replacement feed divided by peNDF of haylage to be replaced.

5 Straw usually limited to 2-4 lb./cow/day for milking cows to formulate diets of sufficient energy density.

6 High forage replacement with cottonseed hulls should coincide with the feeding of coarse-chopped dry hay to provide adequate rumen mat formation. Actual feeding amount should be determined by dietary NDF and NFC guidelines provided in Table 1.

7 Actual feeding amounts may be limited ingredient fat content.

Table 6. Suggested feeding limits for selected high-fiber byproducts 1 .

 

Ingredient

Suggested Limits

lb. DM per cow per day 2

 

 

Alfalfa Meal

5 - 10

Beet Pulp

8 - 12

Brewers Grains

5 - 10

Canola Meal

5 - 10

Citrus Pulp

5 - 10

Corn Gluten Feed

10 - 15

Cottonseed Hulls

5 - 10

Cottonseed Meal

5 - 10

Distillers Grains

5 - 10

Hominy

10 - 15

Linseed Meal

5 - 10

Malt Sprouts

5 - 10

Soybean Hulls

8 - 12

Sunflower Meal

5 - 10

Wheat Middlings

8 - 12

Whole Cottonseed

5 - 8

1 Adapted from Howard (1988).

2 Actual amounts fed should be determined by formulation of diets for requirements and limits for nutrients, such as CP, RUP, RDP, NDF, NFC, fat and P, especially when multiple high-fiber byproducts are used in the same diet.


For more information: R. D. Shaver, Professor and Extension Dairy Nutritionist, University of Wisconsin-Madison/Extension, 608-263-349, rdshaver@facstaff.wisc.edu