Forage Quality Differences of Corn Hybrids as Influenced by Ensiling

Debbie J. R. Cherney, Department of Animal Science, Cornell University, Ithaca, NY 14853; and Jerome H. Cherney and William J. Cox, Department of Crop & Soil Sciences, Cornell University, Ithaca, NY 14853

Abstract

Our objective was to determine the impact of ensiling on forage quality of 54 corn hybrids (Zea mays L.). Four field replicates of each hybrid were planted at each of two locations in NY in 2003 (Groveland Station and Aurora, NY). There were differences among hybrids in pH (P < 0.01) at both sites. The pH of ensiled samples was positively correlated with silage DM (r = 0.82) and increased 0.016 pH units for each 1.0% increase in DM. Crude protein of ensiled samples was highly correlated (r = 0.95) with CP of fresh samples, but CP was 0.41% greater in the ensiled samples. Sugar of fresh samples averaged 9.9% while that of corresponding ensiled samples averaged 3.6%. Ranking of hybrids for sugar changed from fresh to ensiled, but was not consistent between sites. There were hybrid × ensiling/fresh interactions for NDF and IVTD at one site; this interaction was not significant at either site for fiber digestibility (NDFD). There was a significant correlation between fresh and ensiled sample NDFD (r = 0.74, P < 0.01). These data suggest little difference between fresh or ensiled hybrid rankings for NDFD, which implies that differences among hybrids in NDFD could be selected by using fresh samples. Inconsistencies for hybrid × ensiling/fresh interactions indicated that more research is needed to fully assess the relative benefits of ensiling prior to quality comparisons of corn hybrids.

Introduction

Hybrid selection is one of the most important management practices that can affect the feeding quality of corn (Zea mays L.) silage. In the past, many farmers selected silage hybrids based on grain yield and soluble components, but increasing emphasis is being placed on fiber digestion (10). Corn hybrids have been developed with improved forage quality which results in higher energy intake and thus higher milk production (7).

Quality measurements for hybrids are often reported for unensiled hybrids (7). Reasons for this include the time, labor, and expense of ensiling material. In addition, producers must often decide on next year’s corn hybrids before Thanksgiving to obtain the best seed prices, leaving very little time to ensile samples and obtain results in a timely fashion. Quality parameters, including temperature, pH, volatile fatty acids, and aerobic stability, however, can fluctuate during ensiling (5). Increases in protein and fiber and decreases in digestibility have been reported for ensiled versus fresh material (9,14). These differences are not unanticipated and are not an issue if relative ranking of silage hybrids is not altered. No differences in silage hybrid rankings were noted between ensiled and fresh material for forage quality parameters such as NDF digestibility, NDF, CP, or starch (3,7,16). In these studies, however, only from two to four hybrids were evaluated and the hybrids were selected for a wide range in forage quality characteristics. This may have minimized the ability to detect differences in hybrid ranking between ensiled and fresh material. The objective of this study was to evaluate the influence of ensiling using a mini-silo system (4) on forage quality of 54 corn hybrids evaluated in the Cornell University corn silage hybrid trials in 2003.

Determining the Impact of Ensiling on Forage Quality of 54 Corn Hybrids

Four field replicates of 54 corn (Zea mays L.) hybrids were sown at each of two sites in NY in 2003. The Groveland Station location (42°42'N, 77°42'W) is a Hamlin silt loam (Coarse-silty, mixed, active, mesic Dystric Fluventic Eutrudepts). The Aurora location (42°26'N, 76°26'W) is a Honeoye silt loam soil (fine-loamy, mixed, mesic Glossoboric Hapludalfs). The experimental sites were tile-drained, and soil test values indicated high levels of P and K. The experimental sites were plowed and harrow-cultipacked in April 2003. Both sites received about 80 lb/acre liquid starter fertilizer (40-61-0) banded at planting. The Aurora site, which followed soybeans in the rotation, received an additional 134 lb of N per acre at the fifth-leaf stage. The Groveland Station site was on a dairy farm and the field received ample quantities of manure, so no further N fertilizer was necessary.

Five plants from each hybrid × replication at each location were harvested at a 6-inch height at a DM content of about 30% in fall 2003. Plot size was 5 × 15 ft (two 15-ft rows). Hybrids were harvested on the same date at each location. Hybrids were chopped with a chipper-shredder (Mighty Mac LSC506, MacKissic, Inc., Parker Ford, PA) and sub-sampled for fresh and ensiled samples. Though not determined in this study, particle size of corn hybrids using this chipper-shredder in another study (4) indicated that about 90% of material passed a 19-mm screen, about 40% was retained between 19 and 8 mm, about 50% was retained between 8 and 1.18 mm, and less than 10% passed a 1.18-mm screen. Fresh samples were immediately dried at 60°C (15). Ensiled samples (500 g) were vacuum packed in polyethylene bags within one hour of sampling, placed in black plastic bags, and stored at room temperature (23°C) (4). Samples were ensiled for 30 days, upon which bags were opened and samples dried (60°C).

All samples were analyzed for DM, NDF, in vitro true digestibility (IVTD), in vitro fiber digestibility (NDFD), CP, starch, sugar, and nonstructural carbohydrates (NSC, starch + sugar). Samples were analyzed for DM, NDF, IVTD and NDFD in our laboratory. Crude protein, starch, sugar, and NSC analyses were performed by Dairy One (DHI Forage Testing Lab, Ithaca, NY). All ensiled samples were analyzed for pH and a subset of 24 samples was analyzed for fermentation profile.

Fresh and ensiled dried samples were ground through a Wiley mill fitted with a 4-mm screen, followed by grinding with a Udy mill (Udy Corp., Ft. Collins, CO) fitted with a 1-mm screen. Dry matter was determined by drying at 105°C for 24 h (15). Nitrogen was determined by combustion (Leco Instruments Inc., St. Joseph, MI) (2) and multiplied by 6.25 to obtain CP. Neutral detergent fiber was analyzed according to Van Soest et al. (18) using the ANKOM system for NDF. Sulfite and heat stable alpha-amylase were used for NDF analysis of all samples. Starch samples were thermally solubilized, incubated with glucoamylase enzyme to hydrolyze starch and analyzed for glucose using a YSI 2700 SELECT Biochemistry Analyzer (YSI Inc., Yellow Springs, Ohio) (6). Water soluble sugars were analyzed according to the method of Hall et al. (8).

In vitro fiber digestibility was determined according to Cherney et al. (4), using the rumen buffer described by Marten and Barnes (13) and using the Daisy II 200/220 in vitro incubator (ANKOM Technology, Macedon, NY) and the ANKOM 200/220 fiber analyzer (ANKOM Technology, Macedon, NY). The buffer contained urea. Ruminal fluid inoculum was obtained from a non-lactating, rumen-fistulated Holstein cow offered a medium quality orchardgrass (Dactylis glomerata L.) hay diet for ad libitum intake. Samples (0.25 g) were incubated for 48 h at 39°C, and undigested residues were treated with neutral detergent solution. The NDFD was determined using the following formula:

NDFD = 100 —	NDF remaining at t = 48 hours	× 100
	NDF at t = 0 hours

The mini silos were opened at the end of 30 days to determine pH and volatile fatty acids. An aliquot of 50 g wet sample was homogenized with 500 ml of deionized water in a Waring blender (2 min), and filtered through two layers of cheesecloth, prior to measuring pH, and 8.35 ml of 1 M m-phosphoric acid was then added to 25 ml of the extract, which was frozen, and later analyzed for volatile fatty acids [procedure adapted from Wiseman and Irvin (20)]. Fermentation analysis of silage samples was performed by Dairy One. Samples were filtered again through a disposable syringe filter [Millipore Millex 5.0 µm PVDF (Durapore) membrane, Millipore Corp., Billerica, MA] and analyzed for acetic, propionic, butyric, and iso-butyric acids using gas chromatography (1). Lactic acid was determined using an YSI 2700 SELECT Biochemistry Analyzer equipped with an L-lactate membrane. Total lactic acid was determined by multiplying L-lactate by 2.0.

Statistical design was a split-plot with two locations as the main plot and 54 hybrids as the subplot and four replications per site. A split-plot analysis of variance was used to test for statistical significance of treatment effects and interactions using PROC MIXED (12) in SAS, version 7.0 software (SAS Institute Inc., Cary, NC). Ensiling and hybrids were considered fixed effects, while replication was considered a random effect. The Waller-Duncan K-ratio t test option of the LSMEANS statement was used to generate differences among least square means, with comparisons at P ≤ 0.05. Pearson correlation coefficients were determined using PROC CORR in SAS.

Ensiling

Based on fermentation results, all hybrids were well ensiled (Fig. 1). Kung and Shaver (11) report that the typical range of pH for corn silage is 3.7 to 4.2. Kung and Shaver (11) also indicated that lactic acid should be 65 to 70% of total acids. Using these values as indicative of adequate ensiling, all silage samples fell within the value considered adequate for normal fermentation (range 3.43 to 3.91). In addition, there was very little or no propionic acid, butyric acid, or isobutyric acid in any of the corn hybrid samples (data not shown), indicators of poor silage fermentation.

Fig. 1. Relationship between mean silage percent DM at harvest and silage pH for both locations.

There were no significant differences in rankings among hybrids between fresh and ensiled sample DM at either location, as evidenced by the lack of a hybrid*ensiling method interaction at either location (Table 1). There also was a high correlation (r = 0.98, P < 0.01) between fresh and ensiled samples. Ensiled samples were about 1 percentage unit lower in DM than fresh samples. Ensiling usually results in lower DM due to plant respiration (16). Dry matter was highly correlated with pH (r = 0.81, P < 0.01), with every 1 percentage unit increase in silage DM resulting in a 0.016 pH unit increase (Fig. 1). Differences in pH among hybrids was noticable, as indicated previously (4).

Table 1. Means (± standard deviation) and probabilities for DM, IVTD^x, NDF, and NDFD of fresh and ensiled corn silage.

Location	Forage	DM, %	IVTD, % of DM	NDF, % of DM	NDFD, % of DM
Groveland Station	Fresh	26.80 (2.026)	80.3 (2.51)	42.93 (2.374)	54.2 (4.93)
	Ensiled	25.83 (1.858)	78.3 (3.00)	41.25 (3.373)	47.5 (5.41)
		Probability <^y
	Ensiling	0.0001	0.0001	0.0001	0.0001
	Hybrid	0.0001	0.0001	0.0001	0.0001
	Hybrid*Ensiling	0.9985	0.0008	0.0027	0.1718
Aurora	Fresh	32.96 (2.734)	80.9 (2.52)	45.00 (3.044)	57.6 (4.49)
	Ensiled	31.94 (2.673)	81.0 (2.36)	40.43 (2.948)	53.0 (4.90)
		Probability <
	Ensiling	0.0007	0.6523	0.0001	0.0001
	Hybrid	0.0001	0.0008	0.0001	0.0029
	Hybrid*Ensiling	1.0000	0.7971	0.9998	0.5776

^x IVTD = in vitro true digestibility; NDFD = neutral detergent fiber digestibility.

^y Probability level.

Impacts of Ensiling on Fiber Quality

There was a significant interaction between hybrids and ensiling at the Groveland Station site, but not at the Aurora site for IVTD and NDF (Table 1). There was no obvious pattern for this interaction, however, and the correlation between fresh and ensiled hybrids for IVTD and NDF at Groveland Station were still high [r = 0.80 and 0.74 (P < 0.05) for IVTD and NDF, respectively]. The NDFD dropped significantly between fresh and ensiled samples and there were detectable differences among hybrids, but there was no hybrid × fresh/ensiled interaction at either site for NDFD (Table 1). Darby and Lauer (7) also observed lower NDFD in ensiled samples. Sheaffer et al. (16), on the other hand noted increased NDFD in ensiled samples at one site, but not another in a Minnesota study. Lower NDFD of ensiled samples than fresh samples might be expected, as there would be some very digestible NDF that could be utilized during the early stages of fermentation [(17) as cited by (19)]. There was a significant correlation between fresh and ensiled sample NDFD (r = 0.74, P < 0.01) (Fig. 2). These data suggest little difference between fresh or ensiled hybrid rankings for NDFD, which implies that differences among hybrids in NDFD could be selected by using fresh samples.

Fig. 2. Relationship between mean neutral detergent fiber digestibility (NDFD,% of DM) of fresh corn forage samples and NDFD (% of DM) of ensiled corn forage samples for both locations.

Impact of Ensiling on CP Concentrations

Crude protein of ensiled and fresh samples were highly correlated (r = 0.95) (Fig. 3). The slope was was only slightly different from unity and CP was 0.4% units higher in ensiled samples than fresh (Fig. 3). Sheaffer et al. reported lower CP in ensiled corn than fresh corn (16). Thomas et al. [(17) as cited by (19)], on the other hand, reported slightly higher CP in ensiled material, consistent with our observations. Respiration is likely to result in a loss of DM (mostly sugars), which could result in a slight increase in CP of ensiled corn as a percent of DM. Hybrid × fresh/ensiled interactions for CP were not significant (P > 0.05) at either location (Table 2).

Fig. 3. Relationship between mean CP (% of DM) of fresh corn forage samples and CP (% of DM) of ensiled corn forage samples for both locations.

Table 2. Means (± standard deviation) and probabilities for CP, starch, sugar, and NSC^x of fresh and ensiled corn silage.

Location	Forage	CP, % of DM	Starch, % of DM	Sugar, % of DM	NSC, % of DM
Groveland Station	Fresh	7.48 (0.854)	25.83 (4.163)	10.46 (2.858)	36.38 (3.656)
	Ensiled	8.24 (0.863)	28.05 (3.648)	3.84 (1.221)	31.89 (3.338)
		Probability <^y
	Ensiling	0.0013	0.0003	0.0013	0.0032
	Hybrid	0.0001	0.0001	0.0001	0.0001
	Hybrid*Ensiling	1.0000	0.9872	0.0065	0.0034
Aurora	Fresh	5.90 (0.632)	28.86 (3.854)	9.38 (3.039)	38.31 (3.309)
	Ensiled	6.44 (0.691)	30.18 (3.869)	3.38 (1.243)	33.59 (3.737)
		Probability <
	Ensiling	0.0004	0.0066	0.0001	0.0001
	Hybrid	0.0001	0.0001	0.0001	0.0001
	Hybrid*Ensiling	0.9939	0.7540	0.0001	0.7384

^x NSC = nonstructural carbohydrates (sugar + starch).

^y Probability level.

Impact of Ensiling on Starch and Sugar Concentrations

Like CP, starch concentrations of ensiled samples were higher than fresh samples at both sites (Table 2). Hybrid × fresh/ensiled interactions were not significant (P > 0.05) at either site. The correlation between fresh and ensiled forages was high (r = 0.74), although not as high as CP.

Correlations of sugar concentrations between fresh and ensiled samples, although significant (P > 0.05), were not as high as for CP and NDFD (r = 0.60) (Fig. 4). In addition, hybrid × fresh/ensiled interactions were significant (P < 0.05) at both locations (Table 2). Rankings of hybrids changed from fresh to silage, suggesting that some hybrids may have used up more sugar than others during the ensiling process. In addition wetter hybrids had lower pHs than those with higher pHs (Fig. 1) and presumably would have used more sugar to achieve those lower pH values, which could also account for differences among hybrids.

Fig. 4. Relationship between mean sugar content (% of DM) of fresh corn forage samples and mean sugar content (% of DM) ensiled corn forage samples for both locations.

The NSC was lower in ensiled samples than fresh samples at both locations (Table 2), but there was a significant hybrid × ensiling interaction at the Groveland location. The correlation between fresh and ensiled, though significant (P < 0.05) was low (r = 0.30). Part of the reason for the low correlation may be due to the fact that NSC is a calculated value (sugar + starch), and as a result is subject to the cumulative errors of analyzing for these constituents. Much of the difference between the fresh and ensiled NSC is likely due to the depletion of sugar from fresh to ensiled.

Summary and Conclusions

This study focused on evaluating the consistency of change in fiber fractions and digestibility, CP, starch, and sugar from fresh to ensiled samples across a range of corn hybrids. Ranking of hybrids was relatively consistent for NDFD, suggesting that selection for NDFD can be accomplished using fresh samples. Significant hybrid × fresh/ensiled interactions that were different between sites for sugar suggests that some hybrids or samples may use more sugar during the ensiling process than others. Differences in DM content between locations probably contributed to differences between locations for hybrids. More research is needed to fully assess the benefits of ensiling prior to quality comparisons among forages.

Acknowledgments

This research was supported in part by the Cornell University Agricultural Experiment Station federal formula funds, Project No. NYC-1277455 received from Cooperative State Research, Education, and Extension Service, US Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture.

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