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a Dep. of Crop and Soil Sci., Pennsylvania State Univ., University Park, PA 16802
b Dep. of Dairy and Anim. Sci., Pennsylvania State Univ., University Park, PA 16802
* Corresponding author (hdk3{at}psu.edu)
Received for publication March 15, 2002.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: ADF, acid detergent fiber • Bmr, ‘Cargill F657’ (a bm3 brown midrib hybrid) • Conventional, ‘Pioneer brand 3335’ • CP, crude protein • Grazing Maize, ‘Baldridge grazing maize’ • NDF, neutral detergent fiber • TDN, total digestible nutrients
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Research on the management and utilization of corn for grazing is limited. In Hawaii, Singh et al. (1986) achieved animal weight gains that were comparable to gains in a feedlot when a system was developed to optimize utilization of corn at the dough–dent stage by cattle. By moving the cattle to new corn forage twice daily in a small movable pen, wastage was reduced. Mundy et al. (1997) surveyed three beef and dairy producers in Nebraska concerning their use of corn for grazing. Although cattle did not graze the bottom portions of the corn stalks, milk production was maintained, and beef weight gains were acceptable on two of the three farms. All three producers planned to continue grazing corn with some management modifications (Mundy et al., 1997). More recently, in Nebraska, Anderson et al. (2001) reported that it was more profitable to graze corn and supplement beef cattle with protein in autumn than to harvest and sell the grain. A few popular agricultural press articles (Johnston, 1998; Bower-Spence, 1999) have described producer accounts of successfully grazing corn with a range of management practices.
Our objectives were to evaluate grazing corn at two stages of development to meet pasture-based farm forage needs and to compare the economic value of some corn hybrids.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The experimental design was a randomized complete block with four blocks and a split-plot treatment structure. The silking and milk–dough stages of development were the main plots, and corn hybrids were the four subplots. The experiment was started in 1998 at the Pennsylvania State University Dairy Cattle Research and Education Center. The corn plots were established in an area where perennial grass–legume pasture had been grazed and mowed for 10 yr before the experiment. The soil series was Hagerstown silt loam (fine, mixed mesic Typic Hapludalf) with a 0 to 5% slope.
Three weeks before corn planting each year, the pasture sod was killed with a preplant burn-down application of 1.68 kg ha-1 glyphosate [N-(phosphonomethyl)glycine]. After the corn was planted, a pre-emergence application of 1.4 kg ha-1 pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] plus 1.12 kg ha-1 atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] plus an additional 0.42 kg ha-1 glyphosate was applied. Permethrin [3-(phenoxyphenyl) methyl (±)-cis, trans-3-(2,2-dichloroethenyl)-2,2-dimethyl cyclopropanecarboxylate] was also applied at 0.14 kg ha-1 in the pre-emergence pesticide for insect control. The experimental seed corn was planted with a no-till planter at 74 000 plants ha-1 with 38-cm-wide rows. The dates of planting for the 3-yr study were 21 May 1998, 18 May 1999, and 15 May 2000. At planting, 112 and 128 kg ha-1 N and 128 kg ha-1 S were applied in a broadcast application of ammonium sulfate.
In the second year of the experiment, 1999, new seed of the Grazing Maize, Bmr, and Conventional hybrids were planted. Because the silage blend is a new mix each year, seed was saved from the 1998 silage blend to compare the same silage blend with the other three hybrids in 1999. However, the silage blend did not establish well in 1999; therefore, in 1999, the silage blend was not included in the experiment. In 2000, new seed of a new silage blend and the three other corn hybrids were obtained, and all established well. In 1999, two experimental blocks of all four hybrids of the milk–dough stage were not included in the experiment because the heifers broke into two experimental blocks before they matured to the milk–dough stage.
Grazing Management
Eight Holstein heifers that weighed 350 to 400 kg, were 13 to 14 mo old, and had been acclimated to rotational grazing of perennial cool-season grass pastures were used. Before the experiment, the heifers were gradually adapted to grazing corn in an area separate from the experimental plots. Each day for a week, heifers had access to increasingly larger areas of the four corn hybrids until they were adjusted to a 100% corn-grazing diet. We gave the heifers access to equal areas of the four hybrids with adequate corn to meet their voluntary dry matter intake for 24 h.
During the sampling period, all heifers were moved into a new experimental split block each day for 4 d at both stages of development. Each of the four blocks were 12.2 by 21.3 m. In 1998, at the silking stage, eight heifers were given access to split-block plots that were 12.2 by 12.2 m (149 m2), and at the milk–dough stage, the heifers were given access to the rest of the block: plots that were 12.2 by 9.1 m (111 m2). However, the heifers often walked into the plot to strip off leaves and ears of the plants. In the process of walking into the plot, the heifers knocked over many plants that were then contaminated with manure.
Therefore, in 1999 and 2000, we redesigned the blocks so that the heifers faced into a plot that was twice as wide (24.4 m) and half as deep (10.7 m) but with the same total area. At the silking stage, the eight heifers were provided with a block that was 24.4 m wide by 6.1 m deep (149 m2) while at the milk–dough stage, the blocks were 24.4 m wide by 4.6 m deep (111 m2). This forced the heifers to graze from outside of the plot into a wide-faced, shallow block that prevented the heifers from walking deep into the plot to access the entire area and consequently trampling many plants.
Sampling
Immediately before the heifers grazed each block, corn plants were collected to estimate yield by harvesting, at ground level, four randomly chosen 2-m2 subplots for a total of 8 m2 from each of the four hybrids. The four subplots were weighed in the field; then, fresh weight grab samples of approximately 1500 g were obtained in the field. The fresh weight grab samples were taken back to the laboratory and dried in a forced-air oven at 70°C to calculate the dry weight from the fresh weight yield for each hybrid plot.
After the heifers had grazed each block for 24 h, samples were cut at ground level from three different randomly chosen 2-m2 subplots from within each of the four corn hybrid plots. Fresh weight grab samples again were obtained in the field and dried at 70°C to estimate dry matter intake by the heifers. Average dry matter disappearance was calculated as the difference between the before- and after-grazing dry matter estimates. The proportion of the corn that the heifers utilized was also calculated from the estimated dry matter disappearance divided by the before-grazing dry matter estimates in each plot.
For forage quality analysis, a subsample of eight corn plants was selected from the pregrazing yield samples, two from each of the four subplots. Because we observed how the heifers grazed the adjustment corn and previous researchers (Richard Baldridge, personal communication, 1998) found that the heifers usually did not graze the bottom 41 cm of the corn stalks, this section of each plant was weighed and then discarded. The eight plants were then dried again at 70°C and ground through a 1-mm screen. Acid detergent fiber (ADF) and neutral detergent fiber (NDF) were analyzed according to the procedures of Goering and Van Soest (1970). Crude protein (CP) was analyzed according to Isaac and Johnson (1976).
The economic feed value ($ Mg-1 dry matter) of the corn sampled above the bottom 41 cm of corn stalks was calculated on a dry matter basis with the FEEDVAL spreadsheet (Howard and Shaver, 1997) for each experimental plot. The feed value was calculated from the CP and total digestible nutrients (TDN) of the forage. The TDN were estimated from the ADF using the Pennsylvania corn silage equations (Adams et al., 1995). The FEEDVAL spreadsheet also takes the forage Ca and P content into account when estimating the feed value. Because we did not analyze for these nutrients, reference values used in FEEDVAL of 0.02 and 0.3% for Ca and P, respectively, were used. The Pennsylvania State University Dairy and Animal Science Department feed price list for August 2001 (Ishler, 2001) was used to calculate the economic feed values in the FEEDVAL program.
Over the 3 yr, we learned how to manage the corn to decrease wastage and increase the proportion of the corn that the heifers utilized. By the third year, the heifers harvested 71% of the corn at the milk–dough stage (see Table 1). We believe that 71% is a conservative estimate of what the heifers could consume. In this experiment, the heifers were confined to relatively small plots and were not given access to grass pasture. If they had been given access to grass pasture and more space, some researchers and producers report (e.g., Mena Hautau, personal communication, 1998) that cattle lie down and chew their cud on the grass pasture and therefore trample and waste less corn. Therefore, when we calculated the economic yield value ($ ha-1) for each experimental plot, we assumed 71% of the corn yield could be utilized by the heifers. This economic yield estimate for 71% of the yield was multiplied by the economic feed value determined for each plot. Finally, the cost of the seed for each hybrid was subtracted to calculate the economic yield value according to the following formula:
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It is likely that the yields in this experiment were higher than they would be if corn were planted in a field that was previously in corn or soybean [Glycine max (L.) Merr.]. However, again we used a conservative estimate for comparison. When corn is harvested and ensiled, we assumed that about 18% of the dry matter is lost during the harvesting and ensiling process. This can vary depending on conditions of harvesting and ensiling, the type of silo, and silo management (Buckmaster et al., 1989; Rotz, 1995; Rotz and Coiner, 2001). Feeding losses of ensiled forages are typically 5% (Adams et al., 1995). Therefore, about 23% is lost between harvesting and animal consumption. To account for these harvesting, ensiling, and feeding losses, the corn yield at the milk–dough stage for each year was multiplied by 77%.
The economic feed value of a high quality corn silage in the FEEDVAL program using economic feed cost values in the feed price list of the Penn State web site was $87 Mg-1, and the average seed cost for high quality corn hybrid seed was estimated at $100 ha-1. We also accounted for the cost of custom harvesting, hauling, and silo filling using the custom rate of $21.10 Mg-1 (USDA-NASS, 2000, p. 85). We did not account for the cost of fencing and labor to move the heifers when they were grazed, labor to feed heifers in the barn and haul manure, or the fixed costs associated with a silo and animal housing maintenance.
Statistical Analysis
The composition of the silage blend differed between 1998 and 2000, and it was not evaluated in 1999. Therefore, the data from each year were analyzed separately. An analysis of variance for a split-plot design was conducted on the yield, dry matter disappearance, percentage utilized, forage quality (CP, NDF, and ADF), economic feed value, and economic yield data for each year using the General Linear Model procedure of SAS Release 8.2 (SAS Inst., 2000). The main effects, stage of development and the hybrids (the subplots), and the interaction term were considered fixed effects. The error term for the F test for stage of development was the error term for the interaction of stage of development and block; and the residual error term of the model was used for the F test for the main effect hybrid and the interaction term. Standard error for the stage of development was calculated by taking the square root of the mean square error of the stage of development by block as the estimate of variance and dividing by the mean sample size (Steel and Torrie, 1960). The standard error for hybrid was calculated as the square root of the mean square error of the residual error term of the model divided by the mean sample size. Differences were considered significant when p < 0.05, and Tukey's test was employed for the comparison of means.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The percentage of corn that the heifers utilized did not differ between milk–dough and silking stages in any year (Table 1). However, utilization tended to increase over the years, from an average of 55% in 1998 to 63% in 1999 and 69% in 2000. In 1999 and 2000, the depth of corn plots was decreased to prevent heifers from walking into the plots and wasting forage. We suspect our results from these years may be more representative of the utilization that could be obtained if producers provide cattle with access to a narrow long open face of a corn field, to prevent the cattle from walking into a field, trampling, and wasting forage. When we improved management practices to increase utilization of the grazed corn in 2000, the heifers consumed 66% at silking and 71% at the milk–dough stage compared with 77% if fed as corn silage (Adams et al., 1995; Buckmaster et al., 1989; Rotz, 1995; Rotz and Coiner, 2001). With optimum management, this suggests that heifers can graze a proportion of corn at the milk–dough stage that is similar to silage corn that is mechanically harvested and fed. Further, if the heifers had been given access to larger areas and grass pasture than they were confined to in this experiment, observations of producers and researchers (Mena Hautau, personal communication, 1998) suggest that the heifers would trample less corn and utilize more. Regardless of corn silage and grazing corn consumption similarities, when the heifers grazed the corn, they selectively grazed plant parts that were highest in forage quality and feed value (ears, leaves, and stalks above 41 cm from the soil surface).
Forage Quality
Only in 1998 were all of the forage quality variables significantly influenced by the interaction of stage and hybrid (Fig. 1–3). With the exception of CP in 1999, CP, NDF, and ADF differed between stages of development in all 3 yr (Table 4). In 2000, CP, NDF, and ADF differed among hybrids while in 1999, only ADF differed among hybrids (Fig. 1–3).
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Acid detergent fiber. The interaction of hybrid x stage of development was significant in 1998 because at silking, Bmr ADF was 49 g kg-1 lower than Grazing Maize and the silage blend (Fig. 2). By contrast, at the milk–dough stage, Conventional ADF averaged 19 g kg-1 lower than Bmr and the silage blend and 36 g kg-1 lower than Grazing Maize (Fig. 2). Others have found that NDF and ADF decrease as the ear develops and the stover fraction decreases (Coors and Lauer, 2001). This may explain why the low ADF content associated with the Bmr trait is less significant at the milk dough stage compared with other corn hybrids.
In 1999 and 2000, the interaction of hybrid x stage of development was not significant, but the main effects hybrid and stage of development were significant. In 1999, ADF of Bmr averaged 29 g kg-1 lower than that of Grazing Maize and Conventional (Fig. 2). In 2000, Bmr ADF averaged 32 g kg-1 lower than that of Grazing Maize, Conventional, and silage blend (Fig. 2). Oba and Allen (1999) also found that the brown midrib trait was associated with lower ADF compared with other hybrids.
Neutral detergent fiber. In 1998, at the silking stage, Bmr NDF was 26 g kg-1 lower than that of silage blend but did not differ from Grazing Maize and Conventional NDF. At the milk–dough stage, Conventional NDF was 32 g kg-1 lower than the average of Bmr and Grazing Maize and was similar to that of the silage blend (Fig. 3). Because NDF has been found to be predictive of intake (Van Soest, 1994, p. 350), the lower NDF of Conventional at the milk–dough stage may explain the higher disappearance and utilization of Conventional than Grazing Maize in 1998 (Table 3). In 1999, NDF did not differ among the hybrids, while in 2000 Bmr NDF averaged 33 g kg -1 lower than Grazing Maize and silage blend and 18 g kg -1 lower than Conventional (Fig. 3). In both 1999 and 2000, NDF differences were minor, and dry matter disappearance and the proportion of forage that the heifers utilized also did not differ among hybrids (Table 3).
Stage of Development
The CP at the milk–dough stage was lower than at silking by 34 g kg-1 in 1998 and 28 g kg-1 in 2000 (Table 4). Crude protein did not differ between stages in 1999 although it tended to be lower at the milk–dough stage (Table 4). Perry and Compton (1977) also reported lower CP in ears, leaves, and stalks with advancing maturity.
In 1998, 1999, and 2000, the ADF at the milk–dough stage was lower than at silking by 73, 26, and 17 g kg-1, respectively (Table 4). Similarly, NDF was 77 g kg-1 lower at the milk–dough stage than at silking in 1998 and was 33 g kg-1 lower in both 1999 and 2000 (Table 4). The fiber content of the corn at the milk–dough stage was likely lower than at silking stage because it contained more grain (Perry and Compton, 1977). The TDN, as predicted from ADF, were significantly higher at the milk–dough stage than at silking by 48 and 17 g kg-1 in 1998 (675 vs. 627 g kg-1) and 1999 (681 vs. 664 g kg-1). In 2000, TDN tended to be 11 g kg-1 higher (p = 0.08) at the milk–dough stage compared with the silking stage (678 vs. 667 g kg-1).
Economic Feed Value on a Dry Matter Basis
The economic feed value ranged from $89 Mg-1 at the milk–dough stage in 1999 to $99 Mg-1 at the silking stage in 1998 (Table 5). In 1998, there tended to be a significant interaction between stage of development and hybrid (p < 0.07). However, the economic feed value did not differ with the interaction of stage of development x hybrid in 1999 and 2000 nor among hybrids in 1999. In 1998, the economic feed value of Grazing Maize averaged $3.90 Mg-1 higher than that of Conventional and silage blend (p < 0.05, Table 5). In 2000, the economic feed value of Conventional averaged $2.60 Mg-1 lower than that of Grazing Maize and silage blend and was similar to that of Bmr (Table 5). These feed value differences among hybrids appeared to primarily be due to higher CP content of Grazing Maize than Conventional and silage blend in 1998 and to the higher CP content of Grazing Maize and silage blend than Conventional in 2000 (Fig. 1).
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The economic feed value of high quality corn silage as estimated with the same FEEDVAL spreadsheet and Penn State feed price list (Ishler, 2001) was valued at $87 Mg-1. The grazed corn was comparable to or higher in value than high quality corn silage because the heifers selectively grazed the higher quality plant parts. Comparable values calculated with the same FEEDVAL spreadsheet and price list for grass and alfalfa (Medicago sativa L.) silage were $118 and $146 Mg-1, respectively. These perennial stored forage values were higher than the corn silage or grazed corn, probably due to higher CP.
Economic Yield Value per Hectare
The economic yield value of grazed corn (the economic value produced per hectare) ranged from $518 ha-1 at silking in 1998 to $1039 ha-1 at the milk–dough stage in 2000 (Table 5). In none of the 3 yr was the interaction of stage of development x hybrid significant. Because of the higher yield of the grazed corn at the milk–dough stage, the economic yield value was often superior. The silking and milk–dough stages tended to be different in 1998 (p = 0.09) and were statistically different in 2000 (p < 0.05) but not in 1999 when the power of the statistical tests was limited by smaller sample sizes. The average economic yield value over all 3 yr was $641 ha-1 at the silking stage and $826 ha-1 at the milk–dough stage.
Hybrids
Economic yield values did not differ among Grazing Maize, Conventional, and silage blend in all years, except in 2000 when the economic yield value of silage blend was higher than that of Grazing Maize (Table 5). The economic yield value of Bmr hybrid, however, was lower than that of all of the other hybrids, except in 1998 when it was similar to the silage blend (Table 5). This was likely due to a combination of the higher seed cost for Bmr and because the spreadsheet did not credit the economic value of the higher fiber digestibility that is often associated with this hybrid (Oba and Allen, 1999). For high-producing dairy cows, higher NDF digestibility could improve milk production and add value to Bmr (Oba and Allen, 1999).
We estimated the average economic yield value of harvesting the hybrids at the milk–dough stage as whole-plant corn silage in 1998–2000 to be $1058 ha-1. When we accounted for custom harvesting, chopping, and silo filling, the economic yield value was $693 ha-1, or $133 ha-1 less profitable than grazing the corn. This indicates that grazing corn at the milk–dough stage can provide an alternative that is economically comparable to or more profitable than harvesting some corn for silage.
Management Implications
Stage of Development
Delaying grazing by an average of 3 wk for the corn to reach the milk–dough stage resulted in a number of benefits: (i) Yields increased by 2.4 to 6 Mg ha-1, (ii) forage disappearance increased by 2.2 to 4.9 Mg ha-1, and (iii) the economic yield values tended to be higher in 2 out of 3 yr at the milk–dough stage compared with at silking.
As the corn matured from silking to the milk–dough stage, the CP concentration decreased by an average of 30 g kg-1, resulting in a $6.60 to $7.50 Mg-1 lower economic feed value at the milk–dough stage. However, the economic yield values of grazing corn increased from the silking to milk–dough stage by $104 to $310 ha-1 (Table 5) because the corn yields increased by 26 to 50% at the milk–dough stage. And, even though the corn had significant ear development and more mature stalks at the late-milk stage, heifers were able to utilize 60 to 70% of the available forage, leaving mostly the lower stalks in the field. On highly erodible lands, the corn stalk residues could be beneficial for soil conservation purposes.
Grazing corn at the milk–dough stage was also economically favorable to harvesting a similar corn crop for silage by $133 ha-1. However, grazing corn at silking was $52 ha-1 less profitable than harvesting corn for silage. Grazing corn 2 wk earlier than typical for silage harvest (at the milk–dough stage) may permit planting a new perennial pasture or a cereal rye (Secale cereale L.) cover crop afterwards that could also be grazed in late October or November.
Hybrids
The four hybrids rarely differed in yield, dry matter disappearance, or the proportion of corn utilized. Only in 1998, at the silking stage, did the heifers utilize a higher proportion of Bmr than the other hybrids. At the milk–dough stage in 1998, the heifers grazed a higher proportion of Conventional and Bmr than Grazing Maize. Although ADF and NDF of Bmr were lower than ADF and NDF of the other hybrids at some stages in 1999 and 2000, the heifers did not consume or utilize a higher proportion of Bmr or any other hybrid that was superior in ADF and NDF.
None of the hybrids differed significantly in economic feed value ($ Mg-1), except Grazing Maize at the milk–dough stage in 1998. There were also minor differences in economic yield value ($ ha-1) among the hybrids, except for Bmr, which cost more for seed and had a lower economic yield value than the other hybrids in all 3 yr. Therefore, grazing Grazing Maize, Conventional, or the silage blend is likely to be more profitable than grazing Bmr.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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