Milk2000: A New Way to Estimate Corn Hybrid Silage Performance
December 14, 2000 7(28):184
Joe Lauer, Jim Coors, and Randy Shaver
Corn Agronomist, Corn Breeder, and Dairy Nutritionist
Beginning with the 2000 Wisconsin Corn Hybrid Performance Trial Results, ranking
of corn hybrid quality was estimated using MILK2000. Previously, MILK 91 and MILK95
estimated dry matter intake using NDF, and estimated NEL (Mcal/lb) using acid detergent
fiber or in vitro true digestibility. MILK2000 estimates dry matter intake using
neutral detergent fiber and cell wall digestibility (the base dry matter intake
is increased or decreased 0.374 lb. per 1% unit change in cell wall digestibility
above or below the average cell wall digestibility of the trial). NEL (Mcal/lb)
is estimated using a modified summative energy equation. MILK2000 accounts for the
effects of whole-plant DM content and kernel processing on starch digestibility.
A MILK2000 spreadsheet can be obtained at www.wisc.edu/dysci.
In the silage hybrid trials, corn silage was analyzed using near infra-red spectroscopy
equations derived from previous work of Jim Coors and Joe Lauer (UW-Madison).
Plot samples were dried, ground and analyzed for crude protein (CP), acid detergent
fiber (ADF), neutral detergent fiber (NDF), in vitro cell wall digestibility (CWD),
in vitro digestibility (IVD), and starch.
MILK2000 silage performance indices, milk per ton and milk per acre, were calculated
using an adaptation by Eric Schwab and Randy Shaver (UW-Madison Dairy Science Department)
of the MILK95 model (Undersander, Howard and Shaver; J. Prod. Agric. 6:231-235).
In Milk2000, the energy content of corn silage was estimated using a modification
of a published summative energy equation (Weiss and co-workers, 1992; Anim. Feed
Sci. Technol. 39:95-110). In the modified summative equation, CP, fat,
NDF, starch, and sugar plus organic acid fractions were included along with their
corresponding total-tract digestibility coefficients for estimating the energy content
of corn silage. A regression equation developed from literature data was used
to predict total tract starch digestibility from the samples whole-plant dry matter
content. The samples lab measure of CWD was used for the NDF digestibility
coefficient. Digestibility coefficients used for the CP, fat, and sugar plus
organic acid fractions were constants. Dry matter intake was estimated using
the samples NDF content and CWD assuming a 1350 lb. cow consuming a 30% NDF diet.
Using National Research Council (NRC, 1989) energy requirements, the intake of energy
from corn silage was converted to expected milk per ton.
Because the cows maintenance energy requirements were partitioned against the total
diet in MILK2000 rather than against only corn silage as was done in MILK95, there
was a base increase in our new estimate of milk per ton which was of equal value
across all samples that did not influence ranking of hybrids. Milk per acre
was calculated using milk per ton and dry matter yield per acre.