Evaluation of Corn Silage Nutritive Value Using MILK2000

Eric Schwab and Randy Shaver

Department of Dairy Science

University of Wisconsin - Madison

 

 

Background

 

The primary contribution of corn silage (CS) to rations is energy, which makes prediction of its energy content important for diet formulation and economic evaluations.  The contents of crude protein (CP), fat, nonstructural carbohydrate (NSC), and neutral detergent fiber (NDF), and the digestibility of these nutrient components influence the energy content of feedstuffs (Weiss, 1994).  Despite this understanding of the factors affecting the energy value of feedstuffs, most equations to predict the energy content of CS by commercial feed analysis laboratories are based solely on its acid detergent fiber (ADF) content (Chandler, 1990).  This is a major shortcoming of current feed analysis systems for CS considering the recent advances in CS production which affect its energy content, such as harvesting prior to black-layer stage of maturity (Bal et al., 1997), high-oil (Drackley, 1997) and brown midrib (bm3; Oba and Allen, 1999) corn hybrids, and kernel processing (Bal et al., 2000b).

 

When determined by difference calculation (100-CP-NDF-Fat-Ash), the NSC component of CS is comprised of starch, sugars, and organic acids.  Weiss et al. (1992) used a constant digestibility coefficient for the NSC fraction.  However, digestibility of starch is influenced by stage of maturity at harvest (Bal et al., 1997) and kernel processing (Bal et al., 2000b; Dhiman et al., 2000).  Digestibility of NDF is increased for bm3 hybrids compared with conventional hybrids (Oba and Allen, 1999).  To the extent that lignin is related to NDF digestibility, the summative equation of Weiss et al. (1992) accounts for this difference between bm3 and conventional hybrids in their estimate of the energy content of CS.  However, in vitro NDF digestibility (IVNDFD) differences between corn hybrids cannot be incorporated directly into the summative equation developed by Weiss et al. (1992) for estimating the energy content of CS.  Also, we found a poor relationship for corn silage between potentially digestible NDF calculated using the Weiss (1996) lignin sub-equation and IVNDFD.

 

Undersander et al. (1993) presented a method for estimating milk per ton of forage dry matter (DM) as an index of forage nutritive value based on the energy content predicted from its ADF content and DM intake (DMI) predicted from its NDF content.  Again, starch and NDF digestibilities were not taken into consideration in their equations.  Also, Bal et al. (2000a) compared two CS hybrids and reported a poor relationship between estimated milk per ton and actual milk production measured in a feeding trial.

 

Analyses for CS starch and NDF concentrations and in vitro NDF digestibility are available to the industry through commercial feed testing laboratories.  Despite this fact, these analyses were not being used previously in an integrated fashion to estimate the nutritive value of CS.  Our objective with MILK2000 was to incorporate starch and NDF digestibility coefficients into estimates of the nutritive value of corn silage. 

Approach

 

A published summative energy equation (Weiss, 1996), with CP, fat, NSC, and NDF components and corresponding digestibility coefficients, was adapted for corn silage as follows: the CP and fat components were not altered, the NSC component with constant digestibility was replaced with starch and sugar plus organic acid components, the starch digestibility coefficient was varied in relationship to whole-plant DM content and kernel processing, and the NDF digestibility coefficient based on lignin content was replaced by IVNDFD.

 

Regression equations were developed from literature data to predict total tract starch digestibility from whole-plant DM content for unprocessed and processed corn silage.  Slopes of the unprocessed and processed CS starch digestibility regression equations indicate that DM content has a greater impact on the starch digestibility of unprocessed than processed CS.  At 35% DM, predicted total tract starch digestibility for unprocessed and processed CS was 86 and 91%, respectively.  At lower DM contents the difference between processed and unprocessed silage was smaller and increased as DM content increased.  The concentration of the sugar plus organic acid (SUOA) component of CS can be approximated by subtracting percent starch from percent NSC.  Alternatively, analytical values for sugars and organic acids can be used when available.  A digestion coefficient of 100% was assigned to the SUOA component.  A 48-hour or maintenance intake IVNDFD measurement was used in the summative equation. 

 

For the MILK 2000 model, we used our net energy for lactation (NEl) estimates along with DM intake estimated from NDF content and IVNDFD to estimate milk per ton of corn silage DM. 

 

Model Evaluation

 

A comparison of corn silage NEL values at varying whole-plant DM contents while holding ADF and NDF constant was conducted.  The Weiss (1996) summative equation and the ADF-based empirical equations resulted in a constant NEL value across silage DM contents ranging from 30% to 45%. Our equation (Schwab-Shaver; SSE) reduced the NEL value from 0.74 to 0.64 Mcal/lb DM and 0.74 to 0.69 Mcal/lb DM for unprocessed and processed CS, respectively, as corn silage DM content increased from 30 to 45% in relationship to the effects of silage DM content and kernel processing on starch digestibility (Bal et al., 1997; Bal et al., 2000b).

           

A comparison of corn silage NEL estimates from the two summative equations was conducted by varying CS nutrient components.  As starch or NSC content was increased and NDF content was decreased, the corn silage NEL estimate increased for both summative equations.  Processing increased NEL by 0.02 Mcal/lb DM with the SSE.  This effect of processing was unaccounted for with the Weiss (1996) summative equation.  The effects of either increasing IVNDFD (SSE) or decreasing lignin (Weiss, 1996) were evaluated.  While both equations consider NDF and its digestibility, the SSE estimates digestible nutrients from NDF based on IVNDFD and the Weiss (1996) equation uses potentially digestible NDF based on NDF and lignin concentrations.  As IVNDFD was increased at 10%-unit increments, the NEL estimate from SSE increased by 0.05 Mcal/lb DM.  As lignin content was reduced at 1%-unit increments, the NEL estimate from the Weiss (1996) equation increased by 0.02 Mcal/lb DM.

 

A comparison of milk per ton of corn silage DM estimates from the milk per ton model was conducted.  As found for the NEL estimates, the milk per ton estimates were constant for all equations across silage DM contents except the SSE.  Milk production declines as corn silage DM content increases (Bal et al., 1997) and for unprocessed vs. processed CS (Bal et al., 2000b) have been reported.  Milk per ton estimates as corn silage ADF and NDF concentrations or IVNDFD were varied followed similar trends as for NEL estimates.

    

Current Status

 

Near infrared reflectance (NIR) calibrations were available for fresh whole-plant corn samples for all components needed to run MILK2000 except starch.  An NIR calibration was developed for starch.  A comparison of MILK2000 versus MILK95 for reporting the 2000 WI corn silage hybrid performance trial results was conducted.  MILK2000 results appear in the 2000 publication (Lauer et al., 2000).

 

Near infrared calibrations were generally available in commercial forage testing labs for all components needed to calculate the SSE NEl on corn silage samples for nutritionists except IVNDFD.  In fact, wet chemistry IVNDFD was not being done in WI on a commercial basis previously.  The Marshfield Soil and Forage Analysis Laboratory now performs wet chemistry IVNDFD and development of an NIR calibration for IVNDFD on corn silage is in progress.  The SSE summative equations have been made available to commercial forage testing labs and as of 1/01 the AgSource (Bonduel, WI), Dairyland (Arcadia, WI), Rock River (Watertown, WI), and Marshfield labs have programmed these equations into their reporting system.  As of 1/01, the commercial labs are in various stages of development of an NIR calibration for IVNDFD and offering the SSE NEl and milk per ton values to their customers.

 

A Power Point presentation describing MILK2000 and an Excel spreadsheet to calculate SSE NEl and milk per ton are available on the internet at www.wisc.edu/dysci.         

     

References

 

Bal, M. A., J. G. Coors, and R. D. Shaver. 1997. Impact of the maturity of corn for use as silage in the diets of dairy cows on intake, digestion, and milk production. J. Dairy Sci. 80:2497-2503.

 

Bal, M. A., R. D. Shaver, H. Al-Jobeile, J. G. Coors, and J. G. Lauer.  2000a.  Corn silage hybrid effects on intake, digestion, and milk production by dairy cows.  J. Dairy Sci.  83:2849-2858.

 

Bal, M. A., R. D. Shaver, A. G. Jirovec, K. J. Shinners, and J. G. Coors. 2000b. Crop processing and chop length of corn silage:  effects on intake, digestion, and milk production by dairy cows. J. Dairy Sci. 83:1264-1373.

 

Chandler, P. T. 1990. Energy prediction of feeds by forage testing explored. Feedstuffs. 62:36.

 

Dhiman, T. R., M. A. Bal, Z. Wu, V. R. Moreira, R. D. Shaver, L. D. Satter, K. J. Shinners, and R. P. Walgenbach.  2000.  Influence of mechanical processing on utilization of corn silage by lactating dairy cows.  J. Dairy Sci.  83:2521-2528.

 

Drackley, J. K. 1997. Update on high oil corn for dairy cattle. Pages 108-114 in Proc. Four-State Applied Nutrition and Management Conference, La Crosse, WI.

 

Lauer, J., K. Kohn, P. Flannery, and M. Kral.  2000.  Wisconsin Corn Hybrid Performance Trial Results: Grain and Silage.  A3653.  Univ. of WI Extension, Madison, WI.

 

Oba, M. and M. S. Allen. 1999. Evaluation of the importance of the digestibility of neutral detergent fiber from forage: effects on dry matter intake and milk yield of dairy cows. J. Dairy Sci. 82:589-596.

 

Undersander, D.J., W.T. Howard, and R.D. Shaver. 1993. Milk per acre spreadsheet for

combining yield and quality into a single term.  J. Prod. Ag.  6:231‑235.

 

Weiss, W. P. 1996. Estimating available energy content of ruminant feeds. Pages 1-11 in Proc. California Nutrition Conference, Fresno, CA.

 

Weiss, W. P. 1994. Estimation of digestibility of forages by laboratory methods. pp 644-681 in Forage Quality, Evaluation, and Utilization. G.C. Fahey, Jr., ed. Amer. Soc. Agronomy, Madison, WI.

 

Weiss, W. P., H. R. Conrad, and N.R. St. Pierre. 1992. A theoretically-based model for predicting total digestible nutrient values of forages and concentrates. Anim. Feed Sci. Technol. 39:95-110.