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a Horticulture and Crop Science Dep., Ohio State Univ., Columbus, OH 43210-1086
b Ohio State Univ. Ext., Columbus, OH 43210-1086
* Corresponding author (thomison.1{at}osu.edu)
Received for publication November 6, 2001.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Abbreviations: GDD, growing degree days • HO, high oil • HOC, high oil corn • ME, metabolizable energy • NIT, near infrared transmittance • NWBRF, Northwest Branch Research Farm • WBRF, Western Branch Research Farm
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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According to DuPont Specialty Grains and seed companies marketing TC Blends, TopCross HOC has higher oil and protein contents, in addition to a greater concentration of several essential amino acids, than conventional hybrids (Engelke, 1997; Cromwell, 2000; Gaspar, 2000). A more favorable fatty acid composition for feed has also been reported in HOC (Cromwell, 2000; Engelke, 1997). High oil corn is attractive as a livestock feed because it has greater energy value than normal yellow dent corn and can substitute for fats, soybean meal, and synthetic essential amino acids in feed rations (Alexander, 1988; Cromwell, 2000; Kuhn, 1996). The higher nutritional content offers a convenience to livestock producers by eliminating the need to handle and mix fats in ration formulation. Use of HOC can also add value by improving dust control (Kuhn, 1996) and promoting milling efficiency (Brown et al., 2000).
Aside from commercial literature, limited information is available comparing the grain quality attributes of currently grown commercial HOC TC Blends with conventional hybrids. Moreover, little is known concerning effects of varying environmental factors on HOC nutrient composition. According to Lambert (2001), these factors need to be evaluated and understood before large-scale production of HOC is successful.
Most university TC Blend performance trials have not included conventional (low oil) counterparts, which has prevented a comparison of grain quality attributes. Evaluating TC Blends is more difficult than for conventional hybrids due to isolation requirements needed to minimize xenia effects. If pollen from normal yellow dent corn pollinates TC Blend male sterile grain parents, compositional traits associated with HOC will not be expressed.
Growers producing HOC under contracts receive premiums for the elevated oil levels of HOC grain, but not for other potential attributes associated with HOC, including higher protein and essential amino acid levels, and modified fatty acid profiles (Brown et al., 2000). On-farm feeding operations may be able to extract greater value from other nutritional attributes associated with HOC, especially if more information is available on the consistency of these attributes in grain produced across varying growing conditions.
The primary objective of this study was to evaluate the grain oil content of TC Blends and their conventional counterparts across a range of production environments in Ohio. In addition, effects of the TopCross production system on several other economically important grain quality attributes—including protein, starch, lysine, and fatty acid composition—were determined. This evaluation assessed effects of several different types of pollinators that have been used in commercially available TC Blends in the eastern Corn Belt from 1995 to 1999.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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A description of the experimental sites and plot establishment procedures are given in a companion paper (Thomison et al., 2002). Table 1 indicates planting dates associated with each evaluation. In Experiment 1 and On-Farm Study 1, the TC Blends contained a pollinator characterized as a synthetic (R. Bergquist, personal communication, 1995). The pollinators used in Experiments 2 and 3 (and On-Farm Studies 2 and 3) were characterized as pseudo-hybrids, which, according to DuPont Specialty Grains, possess better yield potential than synthetics (S.L. Kaplan, personal communication, 1996).
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In Experiment 2, five TC Blends containing Pfister pollinator 19 (SK3049-19, SK2650-19, SK3001-19, SK2680-19, and SK2652-19) and their respective check hybrids (Pfister brand hybrids 3049, 2650, 3001, 2680, 2652) were grown at NWBRF and the OSU-OARDC Western Branch Research Farm (WBRF) near South Charleston in southwestern Ohio in 1997. The relative maturity and GDD ratings (from VE to R6; Ritchie et al., 1989) of the check hybrids ranged from 108 to 110 d (1450–1540 GDDs).
In Experiment 3, three TC Blends and their respective check hybrids were planted at NWBRF and WBRF in 1998 and 1999. Each TC Blend was associated with a different pollinator. The TC Blends evaluated were DeKalb DK595TC, Pioneer 34K79, Pfister SK3049-19 (in 1998), and Pfister SK2652-19 (in 1999); the check hybrids were DeKalb DK595, Pioneer 34K77, Pfister 3049 (in 1998), and Pfister 2652 (in 1999). The relative maturity and GDD ratings (from VE to R6; Ritchie et al., 1989) of the check hybrids ranged from 108 to 110 d (1450–1540 GDDs).
On-Farm Studies
In On-Farm Study 1, the same TC Blends and check hybrids used in Experiment 1 were established in nonreplicated strip plots at 10 on-farm locations near South Charleston, Washington Courthouse, Columbus, Hebron, Van Wert, and Hoytville in 1995 and 1996.
In On-Farm Study 2, the same TC Blends and check hybrids used in Experiment 2 were established in nonreplicated strip plots at seven on-farm locations near South Charleston, Columbus, Bellefontaine, Hebron, London, Wooster, and Hoytville in 1997. Each on-farm site was in a different Ohio county.
In On-Farm Study 3, five TC Blends containing Pfister pollinator 18 (SK3034-18, SK 2020-18, SK2025-18, SKX777-18, and SK2320-18) and their respective check hybrids (Pfister brand hybrids 3034, 2020, 2025, X777, 2320) were established in nonreplicated strip plots at five on-farm locations near Columbus, Hebron, London, Wooster, and Hoytville in 1997. The relative maturity and GDD ratings (from VE to R6; Ritchie et al., 1989) of the check hybrids ranged from 105 to 107 d (1350–1440 GDDs).
In each experiment and on-farm study, treatments were arranged as a split-plot in a randomized complete block design. Type of corn, high oil (TC Blend) corn vs. check hybrid, was assigned to the whole plot and grain parent was assigned to the subplot. Grain parent refers to the genetic background common to the fertile check hybrid and the male sterile TC Blend grain parent. In Experiments 1, 2 and 3, three replications were used, except in 1995 when five replications were used in Experiment 1. To determine if variation in TC Blend and check hybrid performance was significantly different for the nonreplicated on-farm strip tests, data from the strip tests were combined in each of the on-farm studies with locations treated as replications and analyzed as a randomized complete block split plot (10 replications for On Farm Study 1, 7 replications for On Farm Study 2, and 5 replications for On Farm Study 3).
Due to the limited number of pollinator plants in a TC Blend and the resulting reduction in pollen shed at anthesis, as well as the potential for xenia effects (from neighboring normal corn), these evaluations were conducted using field scale strip plots that would better approximate and simulate comparison of HOC and conventional corn performance in grower fields (Thomison et al., 2002). To minimize contamination of TC Blends by pollen from check hybrids, the following testing protocol was used for comparing TC Blends and their fertile grain parent counterparts. At each location, TC Blend plots were separated from the neighboring check hybrids by 80, 0.76-m rows planted with TC Blend seed. This minimized foreign pollen contamination of the TC Blends. Borders (6.1–15.2 m) on other sides of the isolation field were also planted with TC Blend seed to minimize edge row effects and ensure adequate pollen shed. At all locations, the only nearby foreign pollen source was that of the grain parent check hybrids. This method for evaluating TC Blends and check hybrids is similar to that used by various seed companies (Gaspar, 2000; Thomison et al., 1997).
Because three different pollinators were used in the various TC Blends evaluated in Experiment 3, it was also necessary to group or block TC Blends by their pollinator type to minimize cross pollination. Following guidelines established by DuPont Specialty Grains (S.L. Kaplan, personal communication, 1997), TC Blend blocks with different pollinators were separated by 24, 0.76-m border rows (12, 0.76-m adjacent rows of each pollinator type) to minimize cross pollination.
Following physiological maturity, 10 ears were selected from plants in a 15.2-m length of row in the center of each plot. Ears from obviously stunted or damaged plants were avoided. Because pollinator plants often produced small, poorly developed ears, only ears from grain parent plants were sampled in TC Blend plots. The ears of pollinator plants were distinguished from similar ears of grain parent plants by using kernel appearance, since ears from the latter were characterized by larger, dented kernels with smaller embryos. These ears were shelled and grain samples from each plot were measured for oil, protein, and starch content using near infrared transmission spectroscopy (NIT) analysis (Itnyre, 1992) and oil composition was measured by gas chromatography (Jellum and Worthington, 1966). Metabolizable energy (ME) for nonruminants and lysine were estimated by calculation based on the oil and protein content of samples (Araba et al., 1996). These ME values were an estimate of the feed value of corn grain for swine. Lysine values of grain samples from On-Farm Study 2 (in 1997) and Experiment 3 (in 1998) were determined by liquid gas chromatography according to procedures described by Satterlee et al. (1982) and found comparable to those estimated by calculation (P.R. Thomison, unpublished data, 1997). These grain quality attributes were expressed on a dry weight basis.
For Experiments 1, 2, and 3, data for each trait were subjected to analysis of variance at each location. Data were combined over locations each year for analysis in Experiments 2 and 3. A mixed model was used with locations as random effects, and corn types and grain parents as fixed effects. In each experiment and on-farm study, least significant differences at probability level 0.05 (LSD 0.05) were calculated using the results of the analysis of variance.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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0.05) affected by corn type and grain parent in each experiment (Tables 3 and 4) and on-farm test (Table 5). Averaged across experiments (Tables 6 and 7) and on-farm tests (Table 8), oil levels in grain were 31 g kg-1 higher in TC Blends than for check hybrids. Differences in grain oil content between TC Blends and check hybrids ranged from 26 g kg-1 in Experiment 3 in 1998 (Table 7) to 37 g kg-1 in On-Farm Test 3 (Table 8). Grain parent effects on oil content were nearly always present (Tables 3, 4, and 5). However, the differences in oil levels among grain parents were generally <8 g kg-1 (ranging from 2 to 14 g kg-1 across the different evaluations), and less consistent than the differences between corn types (Tables 6, 7, and 8).
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Yield limiting weather conditions did not adversely affect the increased grain oil content of TC Blends. In Experiment 1 (Table 6), despite late planting and severe drought conditions during grain fill (Table 2), grain oil levels in 1996, averaged across TC Blends, were the same as those in 1995 (69 g kg-1); check hybrid grain oil levels averaged slightly lower in 1996 compared with 1995 (38 vs. 41 g kg-1, respectively). Environment x corn type and environment x grain parent interactions for grain oil content were evident in only one of the three combined analyses (Experiment 3 in 1998; Table 4). The interactions in 1998 may be attributed to varying levels of precipitation at the two sites, above normal at NWBRF, and below normal at WBRF (Table 2), which affected the magnitude of the differences in oil content between corn types and grain parents. In Experiment 3 (Table 7), although growing conditions were much hotter and drier in 1999 than 1998 (Table 2), grain oil levels of TC Blends averaged slightly higher in 1999 (72 vs. 69 g kg-1), whereas check hybrid grain oil levels averaged slightly lower in 1999 compared with 1998 (38 vs. 43 g kg-1, respectively). In Minnesota, Gaspar (2000) evaluated planting date effects on grain oil content of TC Blends and concluded that oil content either increased or did not change with planting dates later than mid-May.
Past studies of conventional hybrids have generally indicated that genetic factors have a greater influence on oil content than environmental factors such as planting dates, location, and year (Jellum and Marion, 1966; Weber, 1987). Earle (1977) evaluated variation in grain oil content by crop years from 1917 to 1977 and found no correlations between the oil content and variations in temperature, rainfall, or fertilization. However, others have reported that severe weather, such as drought during grain fill, can lower oil content (Jurgens et al., 1978).
Grain Metabolizable Energy Content
Nonruminant ME averaged across grain parents, experiments and on-farm tests (Tables 6, 7, and 8) was 130 kcal kg-1 greater in grain from TC Blends compared with check hybrids, which is consistent with previous reports (Engelke, 1997; Gaspar, 2000). Metabolizable energy levels in grain were generally significantly greater in TC Blends than the check hybrids, whereas significant differences among grain parent for ME were less consistent across experiments (Tables 3 and 4) and on-farm tests (Table 5). In Experiment 1 (in 1996) and in On-Farm Tests 1 (1995 and 1996) and 2 (1997), differences among grain parents for ME were not present (Tables 2 and 4). According to Cromwell (2000), the 2.25-fold higher energy content of oil compared with starch results in more ME in HOC (approximately 150 kcal kg-1 more than typically found in conventional corn grain) and gives HOC an advantage over conventional corn as a livestock feed.
Grain Protein Content
According to seed companies and DuPont Specialty Grains (Cromwell, 2000), HOC grain contains up to 10 g kg-1 more protein than conventional grain. However, in this evaluation, protein levels were generally similar for TC Blends and check hybrids. Grain protein content was higher in TC Blends compared with check hybrids only in Experiment 1 in 1995 (Tables 3 and 6). The HO pollinator used in Experiment 1 was different from that used in subsequent experiments and this, along with differences in growing conditions and grain parent genotypes, may have affected HOC protein levels. Recent studies by Lambert et al. (1998) and Strachan and Kaplan (2001) have also found no significant differences in protein levels of conventional corn pollinated by a HO vs. normal oil pollinator.
Grain protein content, averaged across TC Blends and check hybrids, were higher in growing seasons with dry, warm conditions during grain fill—mid-to-late July through mid-September—than in those with cooler, wetter conditions (Table 2). Protein content was 100 g kg-1 for Experiment 1 in 1996 (Table 6) and Experiment 3 in 1999 (Table 7), which had dry conditions during the grain fill period, whereas it averaged 88 g kg-1 for Experiment 2 in 1997 and Experiment 3 in 1998 (Table 7), which had wetter conditions during the grain fill. Grain protein levels also averaged higher (92 g kg-1) for On-Farm Test 1, which included a number of dry sites from 1996, compared with On-Farm Tests 2 and 3 (83 and 84 g kg-1, respectively), which were conducted under the more favorable growing conditions in 1997 (Table 8). Differences existed in some of the grain parent genotypes used in these experiments and on-farm tests, and may have contributed to this variation. However, previous investigations have found similar effects of dry weather on protein content in corn (Genter et al., 1956; Earle, 1977; Jurgens et al., 1978). Decreases in grain protein concentration due to irrigation have been attributed to a decrease in the ratio of horny endosperm to floury endosperm, because horny endosperm has a protein concentration greater than floury endosperm (Bullock et al., 1989).
Grain Starch Content
Starch content, averaged across experiments and on-farm tests, was 5% less in TC Blends compared with the check hybrids (Tables 6, 7, and 8). In recent comparisons of normal and TopCross high oil grain, similar reductions in starch, from 2 to 4%, have been reported (Lambert et al., 1998; Cromwell, 2000; Strachan and Kaplan, 2001). The high metabolic cost of oil synthesis has been cited as the basis for the negative correlations between oil and starch content in corn (Lambert, 2001).
Grain Lysine Content
Lysine levels were higher in TC Blends than in check hybrids in each experiment (Tables 6 and 7) and on-farm test (Table 8). Averaged across experiments and on-farm tests, lysine content was 20% greater in grain of TC Blends. Lysine levels for TC Blends and check hybrids were lowest in Experiment 1, 1996 (2.6 vs. 2.4 g kg-1) (Table 6) and highest in Experiment 3, 1999 (4.1 vs. 3.7 g kg-1) (Table 7). These results are comparable with the increase in lysine content of about 15% reported by seed companies (Cromwell, 2000). Because most essential amino acids are contained in the kernel embryo, increased lysine content in TC Blends is attributed to the larger embryo associated with high oil corn (Lambert et al., 1998). Differences in lysine levels among grain parents were present in each experiment and on-farm test (Table 3, 4, and 5).
The corn type x grain parent interactions observed for oil and the other grain quality attributes (Tables 3, 4, and 5) suggest that the TopCross method had a differential effect on the grain composition of the various TC Blend grain parents evaluated. These interactions could be attributed to differences in magnitude since some grain parents showed a greater change in composition when pollinated by TC Blend pollinators than others (data not shown). Corn type x grain parent interactions were usually found for oil and starch, but were less evident for protein and lysine (Tables 3, 4, and 5).
Grain Fatty Acid Profiles
Oil composition was affected by corn type and grain parent (Tables 4 and 5). The composition of certain saturated (stearic) and monounsaturated (oleic) fatty acids was higher, whereas that of the polyunsaturated (linoleic and linolenic) fatty acids was lower in grain from the TC Blends. Averaged across Experiments 2 and 3 (Table 7), and the three on-farm tests (Table 8), the fatty acid composition of check hybrids was 11.2% palmitic (16:0), 2% stearic (18:0), 25.9% oleic (18:1), 58.8% linoleic (18:2), and 1.3% linolenic (18:3), whereas the composition of the HOC was 11.6% palmitic, 2.5% stearic, 34.6% oleic, 49.5% linoleic, and 1% linolenic. Others (Weber, 1987; Lambert, 2001; Cromwell, 2000) have also indicated that the fatty acid profile of HOC is different from normal corn, being slightly higher in oleic acid and lower in linoleic acid.
Although effects of corn type on palmitic acid composition were not found, except in On-Farm Test 1 (Table 5), palmitic acid composition was consistently affected by grain parent (Tables 4 and 5). Grain parent effects on the composition of the other fatty acids were generally less consistent, and varied considerably among experiments and on-farm tests. Differences in fatty acid composition among grain parents were of a smaller magnitude than the differences between HO and normal corn. The lack of consistent grain parent effects on fatty acid composition may be related to some of the different genotypes evaluated as well as varying weather conditions. The combined analyzes of Experiments 2 and 3 (Table 4) indicated few environment x type interactions for fatty acid composition. Environment x type interactions existed for stearic acid in 1998 and linolenic acid in 1999 in Experiment 3. Similarly, grain parent x environment interactions for fatty composition were limited to palmitic acid in Experiment 2 (Table 4).
There were no corn type x grain parent interactions for the five fatty acids in Experiment 2 (Table 4) and On-Farm Test 1 (Table 5). In Experiment 3, type x parent interactions for fatty acid composition were evident for palmitic and stearic acid for both years, and for linolenic acid in 1998, and oleic and linolenic acid in 1999 (Table 4). Type x parent interactions for fatty acid composition were evident for linoleic acid in On-Farm Test 2, and for palmitic, stearic, oleic, and linolenic acid in On-Farm Test 3 (Table 5).
The limited interactions for fatty acids involving environment, type, and grain parent may make it easier for livestock nutritionists and on-farm livestock producers to use high oil corn in feed rations. Previous investigations have shown limited environmental effects on fatty acid composition of conventional corn (Weber, 1987). Jellum and Marion (1966) studied genotype and environmental effects on corn fatty acids, and found that year, location, and hybrid effects were present, but that the year and location effects were relatively small compared with the hybrid differences.
The increased monounsaturated fatty acid composition associated with HOC may offer several health benefits (Cromwell, 2000). Corn oil with higher levels of monounsaturates reduces blood cholesterol levels, thereby reducing the incidence of cardiovascular diseases (Weaver et al., 2000). Such corn oil is also more chemically stable than conventional corn oil because it is less susceptible to oxidation. The use of corn with a greater content of monounsaturates may improve the food quality of meat (Brown et al., 2000; Cromwell, 2000). Higher levels of monounsaturates used in animal feed result in meat products that remain fresher longer, with less oxidation. Although there have been concerns that use of HOC in swine feed may create soft pork, the reduced levels of polyunsaturated fatty acids and higher levels of saturated fatty acid in HOC may help alleviate this problem (Weber, 1987).
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SUMMARY |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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1 TopCross and TC Blend are registered trademarks of DuPont Specialty Grains, Des Moines, IA. Trade names are used in this article solely for the purpose of providing specific information. Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by The Ohio State University and does not imply approval of the named product to the exclusion of other products that may be suitable. 
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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