Processing Corn Silage

J. HARRISON and L. VAN WIERINGEN
Department of Animal Sciences, Washington State University, Puyallup, Washington

Introduction

The major factor affecting the quality of corn silage is stage of maturity at harvest. Fig. 1 depicts the change in energy value of silage corn as it progresses in maturity. The initial increase in energy content is attributed to accumulation of highly digestible starch in the ear and the high fibre digestibility of the stover fraction of the corn plant. The point of inflection occurs at about 2/3 milk-line stage of the corn kernel (see Corn Growth and Development section). Beyond this point the increased nutritive value in the corn kernel is offset by a decrease in stover digestibility and passage of undigested corn kernels into feces (1). For mechanically processed corn silage, digestibility tends to plateau past 2/3 milk-line due to counteracting effects of increased starch digestibility and decreased stover digestibility.

Figure 1. Relationship between maturity and energy content in
silage corn with and without processing.

How Processing Affects Quality of Corn Silage

Digestion in the Rumen

Our studies have shown that processing corn silage consistently increased total disappearance in the rumen of both starch and fibre (NDF) fractions (Fig. 2). Therefore, processing also tended to improve the rate of whole crop dry matter disappearance in the rumen especially in warm, dry seasons when the silage was relatively dry for its stage of maturity at harvest.

Figure 2. Processing affects rate of dry matter (top) starch (middle)
and neutral detergent fibre disappearance in the rumen.

For both processed and unprocessed corn silages, the amount of disappearance of starch in the rumen was high (> 93%) after 96 hours of incubation (Fig. 2-middle). Despite variability, there was a trend for processed corn silage to have approximately a 3.0 percentage unit improvement in ruminal starch digestibility. Processing particularly improved rate of starch disappearance in drier silages (Fig. 2-middle). Similarly, processing improved rate of fibre (NDF) disappearance most in silage grown under relatively warm and dry conditions (Fig. 2-bottom).

Total-Tract Digestion

The increase in total tract starch digestibility due to mechanical processing was similar to the increase in ruminal starch digestibility. In 11 trials, we found that processing improved total tract digestibility of corn silage by almost 1% unit. This overall increase in digestibility can be attributed to improvements in total tract digestibility of starch (0.84% units), NDF (1.65% units), and fat (0.75% units) (Fig. 3).

Figure 3. Total tract digestibility of dry matter (DM), starch, NDF and fat.

The improvement in NDF digestibility was consistently greatest (4 to 10%) for mature corn silage. This trend was also observed for starch digestibility (1 to 1.3%). The effect of processing on starch digestibility of relatively immature corn (two-thirds milkline) was more variable (0.7 to 2.5%). In unprocessed corn, total tract starch digestibility decreased as the amount of whole intact kernels increased, whereas in processed corn, the amount of intact kernels was minimal so total-tract starch digestibility was always high (Fig. 4-left).

Figure 4. Effect of percent whole intact kernels (top) and post-ensiling
vitreousness (bottom) on whole tract starch digestibility.

The amount of vitreous and floury starch in the kernels in corn silage plays a significant role in total tract starch digestibility (Fig. 4-top). Vitreous starch tends to be harder for cows to digest because the starch granules are embedded in a dense protein matrix. In unprocessed corn silage, as the amount of vitreous starch increases, total tract starch digestibility decreases (Fig. 4). Processing disrupts the dense protein matrix of vitreous starch making it available for digestion. Therefore, total-tract starch digestibility is less influenced by amount of vitreous starch in processed than in unprocessed corn silage.

Energy Content of Total Mixed Rations Containing Processed Corn Silage

We tested the energy contents of the total mixed rations (TMR) containing 27% corn silage (harvested at . milk-line to black-line) which was either unprocessed or processed. These feeding studies involved measurements of all inputs and outputs (Fig. 5). Note that digestible energy (DE) provides the most accurate energy values because it is based on direct measurements of energy consumed (gross energy) minus energy excreted as feces. In contrast, metabolizable energy (ME) and net energy of lactation (NEL) are based on estimates of energy loss in urine, expelled methane and body heat. However the NEL values are particularly useful for ration balancing.

Figure 5. Energy partitioning system

The trials showed that processing of the corn silage improved energy content of the whole mixed ration. The difference in energy content was greater at black-line than at twothirds milk-line stage (Fig. 6). Digestible energy for diets with processed corn silage was about 0.7% greater at two-thirds milk-line and 3.5% greater at black-line than for diets with unprocessed corn silage. The concentration of net energy of lactation (NEL) of processed corn silage diets was about 0.6% greater at two-thirds milk-line and 3.9% greater at black-line than NEL of unprocessed corn silage diets.

Figure 6. Effect of processing corn silage at two stages of maturity on digestible energy (left) and net energy of lactation, NEL (right) of the total mixed ration containing 27% corn silage (for MJ/kg, multiply Mcal/lb X 0.53).

Processing Corn Silage Improves Milk Production

Johnson and Harrison (1) showed that, over 22 trials, cows fed diets based on processed corn silage produced an average of 0.5 kg (range of -0.5 to 1.7 kg) or 1.1 lb (range of -1.1 to 3.7) more milk per day than cows fed diets with unprocessed corn silage (Fig. 8). In addition, processing increased milk fat concentration by 0.08% (-0.18 to 0.29). Hence fat corrected (3.5%) milk production for cows fed processed corn silage based diets was 0.9 kg (0.8 to 2.2) or 2.0 lb (- 1.78 to 4.84) greater than for cows fed diets with unprocessed corn silage. Milk protein concentration was relatively unaffected by processing. Some of the improved milk production can be attributed to increased feed intake, generally 0.5 (-1.5 to 1.4) kg per cow per day or 1.1lb per cow per day (-3.3 to 3.1). Where milk production was not increased by processing, this was due to either decreased feed intake (for unknown reasons) or to inadequate fibre in the diet caused by reduction in particle size (see below).

Figure 8. Effect of feeding unprocessed and processed corn silage on feed intake (DMI) and milk production (left) and milk composition (right) (1 lb = 0.45 kg).

Silage Processing Affects Optimum Chop Length

Processed corn silage should be chopped at a longer theoretical length of cut (TLC) than unprocessed silage to maintain adequate effective fibre in the diet. It is now common to recommend that processed corn silage be cut at 19 to 25 mm (¾ to 1 in) TLC. Table 1 compares performance of cows fed conventional unprocessed corn silage at 10 mm (3/8 in) chop to processed corn silage chopped at 10 mm (3/8 in), 14 mm (9/16 in), and 19 mm (¾ in). For processed corn silage, the longer cuts resulted in less sorting of the diet and provided for the best overall performance (at least equal milk, increased protein and fat, and lower requirement for power).

We recently found that the optimum length of chop for processed corn silage depends on stage of lactation (6). Figure 9 shows that in the first four weeks of lactation, cows performed best on processed corn silage with a relatively short chop (16 mm or 5/8 in), whereas from 4 to 9 weeks, cows performed consistently better on much longer (40 mm or 1 9/16 in) chop lengths.

Figure 9. Effect of chop length of processed corn silage on fat-corrected
(4%) milk production through first 10 weeks of lactation.

 

Table 1.  Effect of chop length and processing on feed intake and production of milk and milk components in kg (lb).

Chop Length

Unprocessed

Processed

 

10 mm (3/8in)

10mm (3/8in)

14mm (9/16in)

20mm (3/4in)

Particle length mm (in)

9.4 (3/8)

6.7 (1/4)

8.9 (1/3)

9.2 (1/3)

Feed intake kg (lb)

25.2 (55.4)

25.9 (56.9)

25.9 (56.9)

25.8 (56.7)

Milk production kg (lb)

44.8 (98.6)

46.5 (102.2)

45.3 (99.7)

46.1 (101.4)

Fat yield kg (lb)

1.3 (3.0)

1.4 (3.2)

1.4 (3.1)

1.4 (3.1)

Protein yield kg (lb)

1.4 (3.1)

1.5 (3.2)

1.5 (3.2)

1.5 (3.2)

 

Does it Pay to Process Corn Silage?

Our economic analysis of processing takes into account many factors such as:

1) Increased costs

  • Increased machinery cost (Shinners, 1999)
  • Higher feed intake

2) Decreased cost

  • Lower storage loss

3) Increased returns

  • More milk
  • Better milk composition (milk fat)

4) Other factors

  • Milk production level
  • % Corn silage in diet
  • Effective fibre in diet
  • Starch digestibility of diet
  • Fibre digestibility of diet
  • Specific energy requirements of harvester
  • Throughput capacity of harvester

Our analysis was conducted using a computer model called DAFOSYM (8) which simulates the economic and environmental aspects of crop production, feed use, and nutrient cycling on a dairy farm (Fig. 10). For example, DAFOSYM can predict how increasing the amount of corn silage in the diet would affect milk production, ration costs, and overall economics at the whole farm level.

Figure 10. DAFOSYM simulates material and nutrient flows for various
dairy farm systems over many years of weather and determines the
economics of the farm.

We tested the economic impact of processing on dairy farms having 100 or 400 high-producing Holstein cows that were fed processed corn silage at 40 and 75% of forage requirement, respectively (Table 2). On the 100-cow farm feeding 40% corn silage, processing improved packing in the silo and increased the digestibility of silage, which reduced requirement for supplemental grain and improved milk production by 2.6%. However, the amount of purchased feed increased because the cows fed processed corn silage were producing more milk and therefore consuming more feed. As in the previous analysis, increases in milk sales exceeded increases in production costs by almost 50/cow/year (Table 2). On the 400 cow farm, feeding processed corn silage for 75% of the total forage requirement, processing increased milk production by about 4% and the economic benefit was $95/cow/year.

Table 2.  Economic Analysis of supplementing processed corn silage in the diet at 40 and 75% of the forage requirement (using DAFOSYM).

 

100 Cow Dairy

400 Cow Dairy

 

40% of forage requirement

75% of forage requirement

 

 UNPROCESSED

 PROCESSED

 UNPROCESSED

 PROCESSED

Corn silage produced, tonne (ton) DM

245 (269)

248 (273)

1810 (1988)

1820 (2002)

*Purchased feed, tonne (ton)

217 (239)

220 (242)

429 (472)

449 (494)

Milk production, kg/cow/year (lb/cow/year)

10,410(22,900)

10,680 (23,500)

10,320 (22,700)

10,770 (23,700)

*Purchased feed & bedding, $

50,042

50,677

178,054

184,044

Net return to management, $/year

44,820

49,605

287,265

325,163

Increase in income due to processing, $/cow/year

-

47.85

-

94.75

* The amount of purchased feed increased because the cows fed processed corn silage were producing more milk and therefore consumed more DM.

Summary

It is commonly agreed that the desirable range of maturity to harvest corn silage is 1/2  to 2/3 milk line or 25-40% DM. If corn silage is mechanically processed before ensiling, as much as 10% additional energy can be gained from the silage. Chop lengths from 5 to 25 mm (¼ to 1 in) can be stored and fed effectively, with longer chop lengths suggested for processed silage. The length of chop should be based on whether or not the silage is mechanically processed and on other forages in the diet.

 

Recommendations for Feeding Processed Corn Silage

Since mechanically processed corn silage has reduced particle size and increased starch digestibility, several practical feeding recommendations are warranted:

1) The greater the amount of processed corn silage in the diet the greater the expected improvement in energy content of the diet.

2) Ensure that there is adequate effective fibre in the diet to avoid milk fat depression.

3) Increase the amount of corn silage in the ration progressively over several days to avoid rumen upset and possible acidosis (see Feeding High Corn Silage Diets section).

Effect of Processing Brown Midrib (bm3) Corn Silage

Does processing increase the silage quality from the highly digestible brown midrib (bm3) corn?

One study, using low ADF diets (15.5-16.5%), found that processing bm3 corn silage with 19-mm (¾ in) chop length did not significantly improve milk production (2, 3). The explanation was that processing increased (whole-tract) starch digestibility but decreased fibre digestibility and processing also reduced eating time. The conclusion was that processing did not affect milk yield because there was very little difference in particle size of material entering the rumen after the initial mastication. A recent study reported that milk production (3.5% fat-corrected) was greater for cows eating processed than unprocessed bm3 corn silage (43.3 vs. 39.3 kg or 95.3 vs. 86.5 lb). The benefit was due to greater in-situ DM disappearance and total tract nutrient digestibility rather than increased intake (4, 5).

 

References

1. Johnson, L. and J.H. Harrison 2001a. Effects of mechanical processing on the nutritive value of corn silage and performance characteristics in lactating dairy cows: 1 Introduction. Washington State University Dairy News. V 10, No 2, March 2001.

2. Schwab, E.C. and R.D. Shaver 2001. Crop processing and chop length effects in brown midrib on dry matter intake and lactation performance by dairy cows. J. Dairy Sci. 84, 197 (Suppl 1).

3. Schwab, E.C. and R.D. Shaver 2001a. Crop processing and chop length effects in brown midrib on chewing activity and mean particle size of silage and masticates. J. Dairy Sci. 84, 197 (Suppl 1).

4. Ebling, L., J.M. Neylon, D.H. Kleinschmit, J.M. Ladd, C.C. Taylor, and L. Kung, Jr. 2002a. Comparison of physical and chemical characteristics of mechanically processed brown midrib, unprocessed brown midrib, or processed normal corn silage. J. Dairy Sci. 85, 383 (Suppl 1).

5. Ebling, L., J.M. Neylon, D.H. Kleinschmit, J.M. Ladd, C.C. Taylor, and L. Kung, Jr. 2002b. Effect of feeding mechanically processed brown midrib (PBMR), unprocessed brown midrib (UBMR), or processed normal corn silage (P7511) in diets for dairy cows on DM intake, milk production and digestion. J. Dairy Sci. 85, 383 (Suppl 1).

6. Johnson, L. and J.H. Harrison 2001b. Kernel processing: Fermentation changes in the silo due to maturity and mechanical processing of corn silage. Washington State University Dairy News. V 10, No 4, May 2001.

7. Bal, M. A., R.D. Shaver, A.G. Jirivec, K.J. Shinners and J.G. Coors 2000. Crop processing and chop length of corn silage: Effects on intake, digestion, and milk production by dairy cows. J. Dairy Sci. 83, 1264-1273.

8. Rotz, C.A., L.M. Johnson, and J.H. Harrison 1999. Economics of corn silage processing on North America dairy farms. Applied Engineering in Agriculture. Vol 15(5), 411-421.

Additional References

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Fox, D.G., C.J. Sniffen, J.D. O’Connor, J.B. Russell, and P.J. Van Soest 1990. The Cornell Net Carbohydrate and Protein System for evaluating cattle diets. Part 1: A model for predicting cattle requirements and feedstuff utilization. Pages 7-83 in Search: Agriculture No. 34. Cornell Univ. Agric. Exp. Stn., Ithaca, NY.

Harrison, J., D. Davidson, and D. Linder 2001a. Evaluation of the nutritive value of low moisture corn silage stored in Ag Bag vs bunker silo. J. Dairy Sci. 84, 154 (Suppl 1).

Harrison, J.H., D. Davidson, and L. Johnson 2001b. Evaluation of processed corn silage harvested at three chop lengths. J. Dairy Sci. 84, 154(Suppl 1).

Harrison, J.H., and L. Johnson 2001. Management practices that enhance the nutritive value of ensiled forages. Proc. 10th International Symposium on Forage Conservation, Brno, Czech Republic.

Harrison, J.H., and L. Johnson 2001. Processed corn silage — what have we learned? Proc. Cornell Nutrition Conf.

Harrison, J. 2001. Corn silage management in bag and bunker silos. Proc. Pacific Northwest Animal Nutrition Conference.

Holmes, B.J. 1998. Choosing forage storage facilities. Proceedings of Dairy Feeding Systems, Management, Components and Nutrients Conference. NRAES-116. Ithaca, NY.

Jirovec, A.J., K.J. Shinners, R.D. Shavers, and M.A. Bal 1999. Processing wholeplant corn silage with crop processing rolls. Presented at the Feb 8-10, 1999 ASAE Ag Equip Tech Conf. Paper # 99AEC-105. Niles Road, St Joseph, MI 49085-9659 USA.

Johnson, L., J.H. Harrison, C. Hunt, K. Shinners, C.G. Doggett, and D. Sapienza 1999. Nutritive value of corn silage as affected by maturity and mechanical processing: A contemporary review. J. Dairy Sci. 82, 2813-2825.

Johnson, L. and J.H. Harrison 2001c. Effects of mechanical processing on particle size, pack density, and aerobic stability of corn silage. Washington State University Dairy News. V 10, No 3, April 2001.

Johnson, L. and J.H. Harrison 2001d. Kernel processing article # 4: Measuring rumen digestibility of processed corn silage using the macro in situ technique. Washington State University Dairy News. V 10, No 5, July/August 2001.

Johnson, L. and J.H. Harrison 2001e. Effects of Mechanical processing on ruminal and total tract digestibility in lactating dairy cows. Washington State University Dairy News. V 10, No 6, September 2001.

Johnson, L. and J.H. Harrison 2001f. Effects of Mechanical processing of corn silage on energy content of TMR fed to lactating dairy cows. Washington State University Dairy News. V 10, No 7, November 2001.

Johnson, L. and J.H. Harrison 2002. Economics of mechanical processing corn silage. Washington State University Dairy News. V 11, No1, February 2002.

Johnson, L., J.H. Harrison, D. Davidson, W.C. Mahanna, K. Shinners and D. Linder 2002. Corn silage management: Effects of maturity, inoculation, and mechanical processing on pack density and aerobic stability. J. Dairy Sci. 85, 434-444.

Johnson, L., J.H. Harrison, D. Davidson, J.L. Robutti, M. Swift, W.C. Mahanna and K. Shinners 2002. Corn silage management I: Effects of hybrid, maturity, and mechanical processing on chemical and physical characteristics. J. Dairy Sci. 85, 833-853.

Johnson, L., J.H. Harrison, D. Davidson, M. Swift, W.C. Mahanna and K. Shinners 2002. Corn silage management II: Effects of hybrid, maturity, and mechanical processing on digestion and energy content. J. Dairy Sci. 85, 2913-2927.

Johnson, L., J.H. Harrison, D. Davidson, M. Swift, W.C. Mahanna and K. Shinners 2002. Corn silage management III: Effects of hybrid, maturity, and mechanical processing on nitrogen metabolism and ruminal fermentation. J. Dairy Sci. 85, 2928-2947.

Johnson, L., J.H. Harrison, D. Davidson, W.C. Mahanna and K. Shinners 2002. Corn silage management III: Effects of hybrid, maturity, inoculation, and mechanical processing on fermentation characteristics. J. Dairy Sci. 85, in press.

Johnson, L., J.H. Harrison, D. Davidson, W.C. Mahanna and K. Shinners. 2002. Corn silage management III: Effects of hybrid, chop length, and mechanical processing on digestion and energy content. J. Dairy Sci. 85, in press.

Johnson, L., J.H. Harrison, D. Davidson, C. Hunt, W.C. Mahanna and K. Shinners 2002. Corn Silage Management: Effects of Hybrid, Maturity, Chop Length, and Mechanical Processing on Rate and Extent of Digestion. J. Dairy Sci. 85, in press.

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