CORN SILAGE TYPES FOR BEST PERFORMANCE

Joe Lauer, Jim Coors, and Randy Shaver

Corn Agronomist, Corn Breeder, and Dairy Nutritionist
University of Wisconsin

Until recently there was little information about the extent of variation for nutritional quality of corn germplasm in the U.S. Past studies on the nutritive value of silage corn emphasized grain to stover ratios and genetic oddities such as the brown midrib mutants. As little as 10 years ago, little information was available for U.S. germplasm. After evaluating nearly 40 different corn hybrids that are typically grown in Wisconsin, Coors (1994) reported that the highest yielding grain hybrids were not necessarily the highest yielding silage hybrids. Furthermore, whole plant digestibility and fiber ranges were rather narrow. In regions of significant silage production such as France, Germany and The Netherlands, corn germplasm has been undergoing selection for forage yield and quality for some time resulting in larger hybrid differences in stover and whole plant digestibility. Recently seed companies have been putting more effort into corn silage hybrid development and have promoted types differing for stover and kernel quality traits. A divergence has occurred with some companies emphasizing “leafy” types while other companies emphasize “digestible stover” types (i.e. brown midrib).

Much debate is currently taking place regarding important traits in grain versus silage hybrids (Table 1). It is generally agreed that most single gene mutants or germplasm stocks exhibiting radically altered morphology (profuse tillering, barren or "sugar" corn, dwarf, etc.) will not have much use as forage types due to their inherently poor productivity compared to adapted hybrids selected for grain production.

Table 1. Important traits for corn grain versus silage hybrid types.
Trait	Grain	Silage
Grain yield	High	Adequate
Forage yield	Adequate	High
Range among hybrids	60 bu/A	8,000 lb Milk/A
Stalks	Standability	Digestibility
Leaves	Unknown	Digestibility
Kernel hardness	Hard	Soft
Plant drydown	“Stay-green”	Synchronous
Plant maturity	“Full-season”	5-10 d longer

Corn hybrid selection is an important management decision in silage production. Silage hybrids should have high forage yield, high digestibility, low fiber levels and stover that is highly digestible. However, many U.S. farmers and livestock producers grow corn for both grain and silage and they decide at harvest, which fields are to be used for each purpose. This flexibility is appreciated because at planting it is difficult to predict overall forage needs later in the year or know the condition of the corn crop at harvest. Acreage of silage production will increase in years when perennial forage legume production is reduced due to winterkill or drought or when moisture stress or early frost limits corn grain production. On the other hand when adequate forage from other crops isn't readily available and corn grain yields are adequate, producers may prefer the option of selling their grain production in the cash market. Selecting hybrids for silage production depends on whether a field is planted specifically for silage or whether the field might be harvested for grain (dual purpose). A dual-purpose hybrid should have both high grain and forage yields.

For both the “dual-purpose” and “silage-only” scenarios hybrid selection should start with identifying a group of hybrids that are adapted to the area in terms of maturity, disease and insect resistance and drought tolerance. Once a group of adapted hybrids is identified evaluate them on the basis of yield potential. Whole-plant yield should be the primary criteria for silage hybrid selection. For the dual-purpose strategy select hybrids with good grain and silage yields. Generally higher silage yields are produced with hybrids that mature slightly later than those adapted for grain production perhaps 5-10 relative maturity units later. In areas with short growing seasons, hybrids should consistently reach harvest maturity just before frost. Other factors such as feed requirements, harvest timing and the potential of wet soils at harvest may dictate the selection of early maturing hybrids.

The final consideration for hybrid evaluation should be quality. Differences exist among commercial corn hybrids for digestibility, NDF digestibility and protein. Most studies have shown that within a group of commercial hybrids there will be a few with superior quality; most with average quality and a few with significantly less than average quality. Many seed companies are developing forage quality profiles of corn hybrids in their product line-up. Ask them for the data.

In 1995 a testing program was initiated to evaluate corn hybrids for silage yield and quality characteristics at the University of Wisconsin in Madison. The cultural practices used to establish these trials were similar to practices and management of growers in surrounding areas with the exception that slightly higher plant populations were used. At harvest whole plant silage plots were harvested using a tractor driven three point mounted one-row chopper. Kernel milk percent, plot weight and moisture content were measured and yields were adjusted to tons/acre of dry matter.

Beginning with the 2000 Wisconsin Corn Hybrid Performance Trial Results, ranking of corn hybrid quality was estimated using Milk2000. Previously, Milk91 and Milk95 estimated dry matter intake using NDF, and estimated NE_L (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). NE_L (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 trials, corn silage was analyzed using near infrared spectroscopy equations. 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 (Tables 2 and 3).  Milk per acre was calculated using milk per ton and dry matter yield per acre.

Forage crop should have high dry matter yield, high protein content, high energy content (high digestibility), high intake (low fiber), and optimum dry matter content at harvest for acceptable fermentation and storage. Predicting animal performance and relating it to improvements in corn silage quality is complex. In numerous studies, differences in fiber and digestibility translate into differences in animal performance. The milk performance indices described above more realistically describe how a forage might perform than specific traits like those described in Table 1 or others such as brown midrib, leafy, etc.).

Differences in milk performance indices calculated using Milk95 and Milk2000 are shown in Tables 2 and 3. Relatively little change in ranking occurred between hybrids for the two different methods. As expected, more mature (drier) hybrids tended to produce lower milk per ton and milk per Acre when calculated using Milk2000. Higher stover digestibility hybrids like brown midrib hybrids had greater milk per ton using Milk2000, but still did not yield as much milk per acre as other hybrids in the test due to poor yield.

Table 2. Relative Performance of Corn Hybrid Types Tested in the UW Silage Trials (1999-2000).
									Milk per Ton		Milk per Acre
Hybrid	Yield	Moisture	CP	ADF	NDF	IVD	CWD	Starch	1995	2000	1995	2000
	T/A	%	%	%	%	%	%	%	lb/T		lb/A
silage	8.5	66.6	7	25	50	74	47	27	1610	2900	13700	25000
Bt	8.5	62.2	7	24	47	74	46	31	1750	2910	14900	24700
HOC	8.2	66.8	8	24	48	75	48	30	1730	3050	14200	25100
leafy	8.4	63.0	7	24	48	74	46	29	1670	2900	14000	24200
average hybrid	8.4	62.5	7	24	48	74	46	31	1700	2890	14400	24300

Table 3. Relative Performance of Corn Hybrids Tested in Six locations (Coors, 2000).
									Milk per Ton		Milk per Acre
Hybrid	Yield	Moisture	CP	ADF	NDF	IVD	CWD	Starch	1995	2000	1995	2000
	T/A	%	%	%	%	%	%	%	lb/T		lb/A
Dairyland 1297	6.4	52.8	7	24	49	73	45	30	1630	2630	10400	16800
Pioneer 35R58	8.2	63.9	7	27	53	70	44	25	1250	2630	10300	21600
NK 48V8 (4687)	8.1	64.7	7	27	53	70	44	22	1280	2680	10300	21600
Cargill F657	5.7	67.5	7	25	50	75	50	27	1690	3110