Poultry, swine and cattle require feed with high calorie levels. High-oil corn is an attractive possibility because it has greater energy than normal corn. Oil contains approximately 2.25 times as much calories as carbohydrates. Broiler diets regularly contain added oil. Dairy cows will more readily exploit bovine growth hormone to its fullest potential if energy is increased beyond that of regular corn rations. Swine treated with porcine growth hormone can expect similar advantages with high-oil diets.

The first high-oil corn varieties were selected in 1896 at the University of Illinois. Over the years genetic selection has steadily improved agronomic performance and yield of corn hybrids with higher oil contents. Corn kernel oil concentration ranges between 1.2 and 21.3% on a weight basis. Commercial hybrids grown in the Corn Belt typically contain 3 to 5 percent oil.

The relationship between oil level and grain yield has been evaluated many times. In the mid 1950's, hybrids derived from the Illinois high-oil project yielded about 10% lower than the best available commercial hybrids. In the mid 1970's, the "Alexho" synthetic hybrids yielded 2-10% below commercially available hybrids. Hundreds of hybrids have been tested over the last 20 to 30 years, but only a few have achieved commercial significance. In general, hybrids with high-oil content have lower grain yield.

Recently there has been much interest in producing high-oil corn from hybrids using the TopCross® system. The TopCross system has the potential of producing greater yields than previously developed high-oil corn hybrids.

A TopCross Blend® is a mechanical mixture of two types of corn seed. One type, representing 90 to 95 percent of the seed in a bag, is a hybrid that is designated as the "Grain Parent." The normal male fertile version is called the "Grain Parent Check." The second type, representing all remaining seed, is a special "Pollinator." The Grain Parent is a male sterile version of an elite hybrid that may already be in commercial production. The Pollinator is a special line, available from DuPont and licenced to the seed company, that sheds pollen within a TopCross Blend production field. The pollen shed from these Pollinator plants contain special genes that cause a kernel to produce a much larger than average germ or embryo (commonly called xenia effect). Since most of the oil and protein is in the germ, the oil, and thus the energy level, and protein quality of the grain produced by fertilization with these pollinators is enhanced.

Pollinator plants contribute little to overall grain yield, but use resources such as soil nutrients, water and sunlight. Their function is to provide pollen to the male sterile Grain Parent. TopCross fields must be somewhat isolated from other "wild" corn pollen sources because wild pollen will not transfer the high-oil trait. Standard seed production procedures, require that corn fields must be isolated by 660 feet from the nearest corn field which would be the source of wild pollen. Most pollen from a plant usually falls within 50 to 100 feet of the plant.

Because of the isolation requirements needed to express the high-oil trait, it is difficult to test these hybrids and evaluate performance. Testing more than one replication, or set of hybrids, at a location is difficult if not nearly impossible. During 1995, in cooperation with a seed company, farmers and county agents, a set of high-oil TopCross Grain Parents and their normal Grain Parent Checks were evaluated at Bangor, Chippewa Falls, Dane, and Janesville, WI. Regular dent Grain Parent Checks were planted on the outside of a block where TopCross Blend Grain Parents were grown. A buffer area of 40 rows was established between the Grain Parent Checks and the Grain Parents. One Pollinator was used in the TopCross Blend area of the field. Grain yield was measured in the middle of rows which were 200 to 300 feet long. Plant populations ranged between 27,500 and 32,500 plants per acre depending upon location. Plot management was similar for all plots. Comparisons were made between the Grain Parent and the Grain Parent Check.

In 3 of 19 comparisons, grain yield of the high-oil Grain Parent was 1 to 7 percent greater than its regular dent Grain Parent Check. In 16 of 19 comparisons, grain yield of the high-oil Grain Parent was 5 to 22 percent lower than its Grain Parent Check. A statistical analysis was made on three hybrids pairs grown at four locations (Table 1). Small differences in test weight and grain moisture at harvest were observed. Oil content increased from 4.5 to 7.0 percent for the Grain Parent Checks and Grain Parents, respectively. Grain yield of the high-oil TopCross Grain Parents averaged 10 percent lower than its regular dent Grain Parent Check.

Agronomically, the TopCross hybrids had similar maturity, standability and disease resistance as the Grain Parent Checks. There were no obvious pollination problems in the trials. Plant populations were similar between hybrid pairs. Although yield decreases were observed, the TopCross hybrids were very close to the performance of the Grain Parent Checks. This has not been the case with other methods of producing high-oil corn, ie. usually yield decreases are more significant and there are other agronomic problems including lodging and disease problems.

Dairy feeding trials show greater dry matter intake of high-oil corn silage, but lower digestibility when compared to silage of normal dent corn. Milk yield and composition and component yields are not different. When feeding high-oil corn grain there is a trend for higher milk production. This is related to higher intake of dry matter for diets containing high-oil grain. No livestock performance trials have been reported using "Top-Cross" blend hybrids.

Producers should consider the following when making a decision about using high-oil corn in their management system:

Grain yield decreases of 5 to 10% (some reports as high as 20%) can be expected with high-oil corn hybrids.
Calorie yield increases may be small. For example, a hybrid with 8% oil will produce approximately 3% more calories per acre than a hybrid with 4.5% oil when both have the same yield.
Marketing opportunities and prices must be known before planting. There are no established markets for high-oil corn, so prices will fluctuate with regular dent corn prices.
If stress should occur around pollination, then the nick of pollen drop could influence grain yield since 90 to 95% of the plants are male-sterile (do not produce pollen).
Isolation from other corn fields is required to adequately express the high-oil trait associated with the "TopCross" Blend.
High-oil kernels tend to be slower in the dry-down process.
Yield differences for high-oil corn silage or grain must be weighed against any potential improvements in animal performance. Producers should try high-oil corn on a few acres before incorporating it into their operation on a large scale basis.

Table 1. Comparison of "TopCross®" high-oil corn with its regular dent corn counterpart.
Hybrid	Trait	Grain yield	Grain moisture	Test weight	Oil content
		bushels/acre	percent	lbs/bushel	percent

Hybrid A	high-oil	136	26.0	53	7.0
	regular dent	154	25.2	53	4.7
Hybrid B	high-oil	146	27.6	54	7.0
	regular dent	158	25.2	54	4.4
Hybrid C	high-oil	147	28.7	53	7.0
	regular dent	165	26.9	52	4.5
LSD0.10		NS	NS	NS	NS

	high-oil	143	27.4	53	7.0
	regular dent	159	25.7	53	4.5
LSD0.10		8	1.0	1	0.3

Mean		151	26.6	53	5.8

References

Alexander, D.E. 1988. Breeding special nutritional and industrial types. In G.F. Sprague and J.W. Dudley (ed.) Corn and corn improvement. Agronomy Monograph 18. ASA, Madison, WI. pp. 869-880.

Dudley, J.W. (ed.). 1974. Seventy generations of selection for oil and protein in maize. CSSA, Madison, WI.

Dudley, J. W. 1977. Seventy-six generations of selection for oil and protein percentage in maize. pp. 459-473. In E. Pollak et al. (ed.) Proc. Int. Conf. Quant. Genet., Iowa State University, Ames, IA. 16-21 Aug. 1976. Iowa State Univ. Press, Ames, IA.

Glover, D.V., and E.T. Mertz. 1987. Corn. In R.A. Olson and K.J. Frey (ed.) Nutritional quality of cereal grains: genetic and agronomic improvement. Agronomy Monograph 28. ASA Madison, WI. pp. 183-336.

Hopkins, C.G. 1899. Improvement in the chemical composition of the corn kernel. Illinois Agric. Exp. Stn. Bull. 55.

Miller, R.L., J.W. Dudley, and D.E. Alexander. 1981. High intensity selection for percent oil in corn. Crop Sci. 21:433-437.

Weber, E.J. and D.E. Alexander. 1975. Breeding for lipid composition in corn. J. Am. Oil Chem. Soc. 52:370-373.