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.

Advantagesof 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 (Bures, 1993). 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 (Coors et al., 1994).

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.

Brown-midribcorn 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 poor early-season vigor, increased lodging, delayed flowering, and poor grain yields.

Starch in kernels of dent corn contain about 75 percent amylopectin starch and 25 percent amylose starch. Waxy corn kernels contain 100 percent amylopectin starch which is totally digestible. Limited feeding trial data suggest that waxy corn equals, but does not exceed, dent corn for forage quality. Waxy corn is very similar to dent corn for yield, standability and other agronomic characteristics.

Sweet cornis 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 dent corn. On a dry matter basis, its nutritive value equals that of immature field corn. When whole plant sweet corn silage is allowed to mature before ensiling, its feed value equals that of dent corn with similar ear-stover ratios. Sweet corn whole plant yields are typically lower than dent corn.

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 when compared to silage of normal dent corn. Yield is usually lower in hybrids with elevated oil levels. Recently much interest has been generated with new high-oil corn hybrids being marketed under the "top-cross" brand. This method involves using between 3 to 8 percent of the plants as pollinators, while the remaining 92 to 97 percent of the plants are high performing male-sterile hybrids. The high oil trait is transferred by the pollen to the kernel via a xenia effect. Testing of the top-cross high-oil hybrids is difficult due to isolation requirements. No university tests have been published on agronomic performance of these new top-cross high oil corn hybrids.

Other corn germplasms such as dwarf corn, autotetraploiud corn, opaque-2, and teosinte-derived germplasm have been evaluated to some extent. General conclusions are that these types are unacceptable for corn silage purposes because of poor whole plant and grain yield. Opaque-2 mutants of corn have elevated levels of lysine and tryptophan. Feeding trials have shown no advantage for these genotypes over dent 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 (Coors et al., 1994). 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 (Coors et al., 1994). 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.

References

Bures, E.J. 1993. Forage quality differences among short season corn hybrids. M.S. Thesis. University of Wisconsin.

Carter, P.R., J.G. Coors, D.J. Undersander, K.A. Albrecht, and R.D. Shaver. 1991. Corn hybrids for silage: an update. 46th Ann. Corn and Sorghum Res. Conf., American Seed Trade Association, Washington, DC.

Coors, J.G., P.R. Carter, and R.B. Hunter. 1994. Silage corn. In Specialty corns. CRC Press.