Currently, there is much interest by producers and seed companies in evaluating corn hybrid silage performance. Wisconsin is the largest corn silage producing state in the U.S. Between 1989 and 1993, corn silage was grown on 570 000 to 950 000 acres, which accounted for 15 to 28 percent of the total corn acreage in Wisconsin. In the past, university and seed company agronomists have suggested that the best grain hybrids were also superior hybrids for silage yield and quality. Most producers grow corn for both grain and silage purposes with the final use decision being made at harvest. High grain yield does not necessarily correlate with forage quality. Most producers are aware that there is considerable genetic variation for nutrition value among corn hybrids. Corn hybrid silage yield and quality differences can be economically important to dairy and livestock operations.

Advantages of corn silage include: 1) a palatable forage with relatively consistent quality and higher yields and energy content than most other forages, 2) requires significantly less labor and machinery time than other harvested forages due to only a single harvest activity, 3) cost per ton of dry matter also tends to be much lower than for other harvested crops. Disadvantages include: 1) few established markets for silage sales, 2) transportation costs are high so the crop must often be fed near the farm where it is produced, 3) storage facilities tend to be more expensive than those for dry hay, 4) where corn is not well adapted, the cost of production may be too high to warrant corn silage production, 5) on erodible soils corn silage production may be limited due to residue requirements in soil conservation programs.

Corn silage is primarily an energy supplying forage with its nutritive value related to digestibility and factors that affect digestibility such as intake and fiber. Silage quality of dent corn has been reported to range from 54 to 86 percent dry matter digestibility, 7 to 11 percent crude protein, 23 to 43 percent acid detergent fiber, and 40 to 68 percent neutral detergent fiber. Whole plant dry matter yields in Wisconsin have been as high as 11 ton per acre. The range in silage quality parameters may be smaller than the range in yield for corn hybrids developed for specific environments. The large range in digestibility and other silage quality parameters reported in the literature can be attributed to hybrid differences in maturity, grain-to-stover ratio, grain composition, stover composition, and methods of forage analysis.

Plant breeders have developed several types of corn differing in their silage characteristics. These corn types may have silage quality advantages, but usually are poor performers agronomically when compared to dent corn because of yield or standability deficiencies.

Desirable silage characteristics include 1) high dry matter yield, 2) high energy content, 3) high intake, and 4) optimum dry matter content at harvest for acceptable fermentation and storage. Corn silage is primarily an energy supplying feed, and its nutritive value is related to digestibility and factors that affect digestibility.

Several types of corn are available from corn breeders that differ in their genetic makeup and may affect silage characteristics (Table 1). These include brown-midrib, waxy, sugar or grainless, sweet corn and high-oil corn. Usually these types of corn are agronomically poor performers because of yield or lodging.

Table 1. Range in relative dry matter yield and forage quality characteristics of dent corn and other corn germplasms.
	Dry Matter Yield	Digestibility	Crude protein	Fiber ADF : NDF
	relative to dent corn	%	%	%
Dent corn	100	49-72	7-11	23-43 : 40-68
Brown mid-rib	81-90	56-69	7-10	21-39 : 37-65
Sweet corn	39-100	65-69	7-9	--- : 45-50
Pop corn	39-69	66	7	--- : 51
Opaque-2 hybrids	93	63-68	7	20-26 : ---
Waxy hybrids	96-114	69	8-11	22-37 : 41-57
High-oil hybrids	---	71	9	--- : 40
Tillering hybrids	62-161	60-66	6-9	29-37 : ---
Dwarf genotypes	83-100	60-70	9	--- : 65
Autotetraploids	100-113	62-73	7-8	--- : ---
Teosinite	82-145	---	8-9	--- : ---

Brown-midrib corn has reduced lignin levels in stalks and leaves compared to lignin levels in normal corn plants. Since lignin is undigestible, brown-midrib corn plants should be more digestible than normal corn plants. Increased digestibility is usually found in the stover of brown-midrib types. However, animal performance in feeding trials is inconsistent. Agronomic evaluations have shown slower growth rates, poor early season vigor, increased lodging, delayed flowering, and poor grain yields.

Normal corn starch contains about 75 percent amylopectin starch and 25 percent amylose starch. Waxy grain contains all amylopectin starch. Limited feeding trial data suggest that waxy corn could equal, but not exceed, normal corn for forage quality. Waxy corn is very similar to normal corn for agronomic characteristics.

Sweet corn is often available for ensiling as canning factory waste, stover, and as whole plants. Canning factory waste consists of husks, cobs, and some ears. This silage is usually lower in protein and energy than silage made from eared field corn. On a dry matter basis, its nutritive value equals that of immature field corn. Sweet corn stover left after removing the ears for the factory has more nutritive value than stover from ripe field corn due to greater leafiness, and greener leaves and stalks. Whole plant corn silage is made by allowing the plant to mature before ensiling, and its feed value equals that of field corn with similar ear-stalk ratios. A disadvantage of sweet corn is its slow grain dry down rate which means it must be harvested later than field corn. This not only delays harvest and increases the risk of spoilage, but reduces stover quality due to increased lignin and fiber concentrations.

High-oil corn has greater energy than normal corn because the calorie content of oil is approximately 2.5 times as great as that of carbohydrates. Feeding trials show greater dry matter intake, but lower digestibility than silage of normal corn. Field yield losses have been associated with elevated oil levels.

Opaque-2 mutants of corn have elevated levels of lysine and tryptophan. General nutritional value of this silage was similar to normal corn silage. Feeding trials have shown no advantage for these genotypes over normal corn.

Regular dent corn hybrids will continue to be used for both grain and silage purposes and will be the predominant germplasm source for many years to come. Breeding activity by seed companies has led to development of dent corn hybrids with claims of improved silage quality. Previous studies indicate that differences do exist for commercial dent corn hybrids. These small differences might be economically significant.

No hybrids are screened routinely for silage quality by University hybrid evaluation programs. Producers should select corn hybrids based on grain yield potential, standability, and pest resistance. If the decision is made at planting to grow corn for silage, then a slightly longer season hybrid (about 5 to 10 relative maturity units) should be considered. Once a high performing corn hybrid is identified, the producer should consult with the seed company representative for information on the relative quality ranking of the hybrid among the hybrids being marketed within the company.

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