Shredlage Processing Affects the Digestibility of Maize Silage

Abstract

Maize silage is one of the most important feeds for ruminant nutrition and various production methods can have a significant impact on their quality, especially the utilization of nutrients. The objective of the study was to evaluate the effect of conventional and shredlage processing of harvested maize on kernel processing, fermentation profile, physically effective fibre and digestibility of maize silage. A stay-green maize hybrid was harvested with a conventional forage harvester (CON; theoretical length of cut 10 mm; conventional rollers with a 30% difference in roller speed; the rollers have a horizontally teeth; 1-mm roll clearance) or a shredlage processor (SHR; theoretical length of cut 25 mm; Shredlage crop processor with 50% difference in roller speed; the rollers have sawtooth teeth with a counter-rotating spiral groove; 1-mm clearance) and stored in experimental silos. The experimental silages were analysed for chemical composition (dry matter, organic matter, crude protein, crude fibre, neutral detergent fibre, starch), fermentation parameters (pH, lactate, acetate, ammonia), processing quality (kernel processing score, particle size), physically effective neutral detergent fibre (peNDF) and in vivo nutrient digestibility. The shredlage processing (SHR) of maize plants did not have an effect on the silage fermentation profile. On the other hand, the SHR treatment significantly increased kernel processing score (p < 0.01) and peNDF content (p < 0.01). SHR also increased in vivo digestibility significantly, namely that of dry matter (DM), organic matter, starch, crude fibre and neutral detergent fibre (NDF). An increase in nutrient digestibility leads to higher values of NEL. The presented results show positive effects of shredlage processing on quality and digestibility of maize silage.

1. Introduction

Maize silage is one of the most important feeds in the ruminant diets due to its high energy content and the yield of forage biomass [1]. Saylor et al. [2] postulated that aggressive kernel processing and prolonged storage have the potential to improve starch availability of maize silages.

Over the past decade, there have been efforts to improve kernel processing of whole-plant maize silage using forage harvesters equipped with onboard processing rolls. Dairy cows require diets with adequate particle size to maintain healthy rumen function [3]. Whole plant maize silage is simultaneously a source of physically effective fibre and energy for the dairy cow [2]. The particle size distribution of forages and TMR can be determined with the Penn State Particle Separator [4]. Because particle size distribution is important to the animal, a description of the length distribution of feed particles (rather than the mean length only) is needed for proper nutritional management [5]. However, only 30% of maize silages had Penn State Particle Separator distributions that conformed to the recommendations of Kononoff and Heinrichs [6], and 30% of maize silages also had average particle lengths that were lower than these recommendations [7].

Increasing the theoretical length of cut beyond 19 mm and increasing roll clearance of kernel processing may potentially reduce nutrient digestibility and animal performance [8]. Smaller forage particles spend less time in the rumen and are less available to microbial digestion; this decreases digestibility, particularly that of fibre because of its relatively slow rate of digestion [9].

In the present study, the conventional processing and shredlage processing of maize for silage making were compared and evaluated. Conventional processing is designed for the production of silage with a length of cut from 3.5 to 22 mm, using crushing rollers with longitudinal teeth with the task of breaking (crushing) corn grains. On the contrary, shredlage processing is designed for the production of silage with a length of cut from 22 to 30 mm, which could be important for the preparation of feed rations with an optimal structure. At the same time, the shredlage processor has the rollers with a counter-rotating spiral groove, so that as the maize material passes through the rollers, it is also pulled apart by the sideways movement of the teeth, so that the cob pieces are fully broken down and the kernels are crushed to break, and at the same time also the stalk material is shredded very effectively in the longitudinal direction and the bark is peeled off by this rollers. Shredlage rollers has also higher difference in roller speed in comparison with conventional ones.

Potential improvements in starch digestibility appears to be an important benefit of the cross-grooved processing rolls, used in the harvest of shredlage. The total-tract starch digestibility of maize silages, however, ranges from about 80 to 98% in lactating dairy cows fed diets, based on maize silage [10]. Processing whole plants through rollers during the harvest reduces the particle size of maize kernels and has been reported to increase the total-tract starch digestibility [11].

The objective of the current study was to evaluate the effect of conventional and shredlage harvest processing on kernel processing, fermentation profile, physically effective fibre and the digestibility of maize silage.

2. Materials and Methods

2.1. Experimental Material

The stay-green maize hybrid Agro Vitallo (FAO 280, KWS) was grown in operating conditions in 2 consecutive years at a density of 90,000 plants per hectare. The maize stand was harvested during 1 day, either for conventional silage (CON; theoretical length of cut 10 mm; conventional rollers with a 30% difference in roller speed, the rollers have a horizontally teeth; 1-mm roll clearance) or shredlage (SHR; theoretical length of cut 25 mm; shredlage crop processor with 50% difference in roller speed, the rollers have sawtooth teeth with a counter-rotating spiral groove, with 1-mm clearance) by Jaguar forage harvesters (Claas Saulgau GmbH; Bad Saulgau; Harsewinkel; Germany). The silages were made manually and stored in 1-m³ experimental silos (1 silo per processing and year, experiment was replicated in 2 years). The silo was made from an IBC container where two layers of silage tarpaulin were inserted. After filling, the silo was closed by silage tarpaulin, and the silage was loaded with ballast bags. Silage filling density was around 670 kg/m³. They were stored under the same conditions for 2 months. Then the experimental silos were opened, and silage samples were subjected to chemical analyses, evaluation of particle size distribution and kernel processing and determination of nutrient digestibility. The analyses and evaluations were performed on three samples from each silage.

2.2. Chemical Analyses

The samples for chemical analyses were dried at 50 °C for 48 h [12] and then milled (Retsch SM 100; Retsch GmbH, Haan, Germany) through a 1-mm sieve and subjected to chemical analyses. Residual moisture was determined by oven drying for 6 h at 105 °C. Ash content was determined after 6 h at 550 °C. Ether extract (EE) was measured after 6 h of petroleum-ether extraction according to the AOAC Official Method 2003.05 [13]. Nitrogen was determined by the Kjeldahl method, according to the AOAC Official Method 976.05 [13], and crude protein (CP) was calculated as N × 6.25. The crude fibre was determined according to the AOAC Official Method 962.09 and is presented as ash free. The aNDFom concentration was measured according to the AOAC Official Method 2002.04 [13] and was analysed in the presence of sodium sulphite and with α-amylase treatment and is presented as ash free The ADFom was determined according to the AOAC Official Method 973.18 and is presented as ash free. All fibre analyses were adapted for an ANKOM220 Fiber Analyzer (ANKOM Technology Corporation, Macedon, NY, USA). The starch was analysed according to the AOAC Official Method 920.40 [13]. Fresh silage samples were analysed for fermentation quality (pH, concentrations of lactic, acetic and butyric acid) according to Kvasnička [14] using IONOSEP 2001 analyser (RECMAN–laboratory systems, Ostrava, Czech Republic).

2.3. Quality of Processing and Physically Effective Fibre

Particle size distribution of silages was determined using the Penn State Particle Separator with 19-, 8- and 4-mm sieves plus a bottom pan. The 300 g wet samples of silages were shaken on Penn State Particle Separator with 40 movements (5 movements in each direction, twice). Pef (ranging from 0 to 1) is determined as the proportion of particles (DM basis) retained by the 19.0 and 8.0-mm sieves [15]. The peNDF (physically effective neutral detergent fibre) content of silages was calculated by multiplying the physical effectiveness factor (pef) and dietary NDF content. The kernel processing score was measured as a percentage of the starch particles passing through the 4.75-mm sieve [16].

2.4. In Vivo Study

The experimental protocol was approved by the institutional Animal Care and Use Committee, Institute of Animal Science, Prague, Czech Republic (Act No. 359/2012 Coll.). Six Romanov sheep (wethers) of similar body weight were divided into two groups and were used in repeated 2 × 2 factorial design (2 groups × 2 treatments). In each repetition, the animals were housed in individual stalls and fed a diet based on (a) conventional maize silage (CON) or (b) maize shredlage (SHR) for 14 days (preparing period). Thereafter, the wethers were individually housed in metabolic cages for a five-day trial (sampling period). The same method was used for silages from both years. The silages were offered in two equal meals at 7:00 a.m. and 6:00 p.m. The animals had free access to water during the whole 19-day experiment. Body weight was measured on days 0 and 19. Feed refusals and faeces were sampled every day, pooled into a plastic bag for each animal and stored in the freezer. The samples of feed and refusals were oven-dried at 55 °C and faecal samples were freeze-dried (freeze dryer Alpha 1–4 LSC, Martin Christ Gefriertrocknungsanlagen GmbH, Osterode am Harz, Germany) to a constant weight, then milled through a 1-mm sieve (Retsch SM 100; Retsch GmbH, Haan, Germany) and analysed for ash, dry matter (DM), CP, fibre fractions, EE and starch. Energy (MJ NEL/kg DM) was calculated based on measured chemical composition and nutrient digestibility values, using the equations by Vencl et al. [17].

2.5. Statistical Analyses

All data were analysed with the GLM procedure of SAS (SAS Institute Inc., Cary, NC, USA, 2002). The methods of maize silage processing, harvest year and their interactions were used as fixed effects in the model for evaluation of chemical composition, fermentation profile and particle size distribution. Replicates were used as random factors in the model. Nutrient digestibility was compared, based on the method of silage processing, year of harvest and their interactions as fixed effects in the model and animals were used as a random effect. The comparison of means was performed with the Tukey–Kramer test.

3. Results

3.1. Chemical Composition and Fermentation Quality of Maize Silages

The chemical composition and fermentation profile is presented in

Table 1. Chemical composition and fermentation profiles of maize silages harvested using conventional or shredlage processing.

Year	1		2			p-Value
Processing	CON 1	SHR 2	CON	SHR	SEM	PR 3	Y 4	PR*Y 5
Dry matter, g/kg	343 b	355 a	327 c	306 d	2.6	0.009	<0.001	<0.001
Nutritional composition, g/kg DM
Crude protein	77.8	82.5	83.0	84.3	1.0	0.017	0.009	0.114
Ether extract	31.2	32.6	24.5	20.2	1.3	0.277	<0.001	0.055
Crude fibre	210	200	210	211	5.8	0.502	0.333	0.376
Organic matter	965	963	964	965	0.8	0.372	0.173	0.060
aNDFom	438	432	443	434	11.8	0.534	0.792	0.913
ADFom	217	209	209	223	4.3	0.510	0.482	0.166
Starch	331	337	361	361	9.7	0.760	0.023	0.809
Fermentation profile, g/kg DM
pH	3.92	3.94	3.94	3.90	0.02	0.471	0.602	0.150
Lactate	44.7	41.2	21.2	20.1	3.5	0.480	<0.001	0.702
Acetate	16.0	14.5	7.9	9.2	1.8	0.955	0.008	0.455
Ammonia, g/kg CP	49.0	45.1	42.3	33.0	4.1	0.146	0.010	0.524

¹ CON: conventional processing; ² SHR: shredlage processing. ³ PR: processing. ⁴ Y: year. ⁵ PR* Y: interaction between processing and year. ^{a, b, c, d} Means within the rows with different superscripts indicate a significant difference at p < 0.05.

. The silages differed in DM content. The CON and SHR silages had mean DM of 335 g/kg and 330 g/kg, respectively. The biggest differences were between the first and second harvest year (349 g/kg vs. 316 g/kg, respectively). However, DM content had no effect on DM losses, which were since 4.8 to 5.1% (not tabulated). SHR silages had a higher CP content than CON silages (83.4 vs. 80.4 g/kg DM, respectively). The CP content differed also between the years (80.2 vs. 83.7 g/kg DM). There were find also differences in EE between years (31.9 vs. 22.4 g/kg DM) in this study. The silages under study were not different in the other chemical parameters. The starch content did not differ between the processing methods but was different between the 1st and 2nd years of harvest (334 vs. 361 g/kg DM). The processing method had no effect on fermentation profile of silages. The silages made in the 1st year had higher amounts of acids than those made in the 2nd year; however, there were no differences between the silages made in the same year.

3.2. Particle Size and Kernel Processing of Maize Silages

The quality of maize silage processing can be described by kernel processing score (percentage of starch particles passing through a 4.75-mm screen). This parameter was markedly increased by the SHR treatment compared to CON (67.2 vs. 54.6%, respectively). A higher processing score for SHR was detected in both years (

Table 2. The effect of processing on the quality of kernel processing and particle size.

Year	1		2			p-Value
Processing	CON 1	SHR 2	CON	SHR	SEM	PR 3	Y 4	PR*Y 5
Processing score %	57.7 c	66.7 b	51.6 c	67.6 a	0.45	<0.001	<0.001	<0.001
Penn State separator sieves, % as fed retained
19.0 mm	2.20 b	18.8 a	0.63 c	7.74 bc	0.85	<0.001	<0.001	0.001
8.0 mm	62.5 a	53.1 b	55.4 b	60.3 a	1.50	0.161	0.946	0.002
4.0 mm	21.3 b	16.7 c	32.4 a	21.5 b	1.21	<0.001	<0.001	0.032
Bottom pan	14.0	11.4	11.6	10.5	0.83	0.057	0.072	0.396
Parts up 8 mm	64.7	71.9	56.1	68.1	1.21	<0.001	0.001	0.082
peNDF	283	311	248	295	7.5	0.001	0.009	0.221

¹ CON: conventional processing; ² SHR: shredlage processing. ³ PR: processing. ⁴ Y: year. ⁵ PR* Y: interaction between processing and year. ^{a, b, c} Means within rows with different superscript letters indicate a significant difference at p < 0.05.

). The percentage of silage particles retained on the top screen of the Penn State Particle Separator was higher for SHR than CON (13.3 vs. 1.4%, respectively). Differences were found out also between the years. The percentage retained on the top two screens was also higher for SHR compared to CON (70.0 vs. 60.4%, respectively). This was consistent with the peNDF content being higher in SHR than in CON (303 vs. 266 g/kg DM, respectively).

3.3. Apparent Digestibility of Total Tract

Table 3. Effect of maize silage processing on in vivo digestibility of nutrients.

Year	1		2			p-Value
Processing	CON 1	SHR 2	CON	SHR	SEM	PR 3	Y 4	PR*Y 5
Digestibility, % of intake
Dry matter	66.3	71.4	67.1	69.1	1.16	0.002	0.428	0.130
Organic matter	67.8	72.9	68.3	70.3	1.19	0.002	0.283	0.120
Crude protein	48.2	48.1	59.4	58.4	1.61	0.743	<0.001	0.767
Crude fibre	41.6	50.0	44.6	48.8	2.33	0.004	0.635	0.263
aNDFom	47.7	56.6	48.2	51.0	2.12	0.004	0.161	0.099
Starch	95.8 b	97.9 a	99.4 a	99.6 a	0.44	0.020	<0.001	0.040
Ether extract	87.2	87.2	86.8	85.0	1.20	0.463	0.269	0.461
Energy, MJ NEL/kg DM	6.17	6.37	6.31	6.39	0.06	0.015	0.112	0.241

¹ CON: conventional processing; ² SHR: shredlage processing. ³ PR: processing. ⁴ Y: year. ⁵ PR* Y: interaction between processing and year. ^{a, b} Means within rows with different superscript letters indicate a significant difference at p < 0.05.

presents the total tract nutrient digestibility values for the tested maize silages found in sheep. The processing method did not affect CP and EE digestibility (53.8% and 87.0% vs. 53.3% and 86.1% for CON vs. SHR, respectively). The CP digestibility differed also between the years with a higher digestibility was found in the second year (p < 0.01). Starch digestibility was affected by the processing method (97.6 for CON vs. 98.7% for SHR) and also by the year (96.8% in the first year vs. 99.5% in the second year). The other nutrient digestibilities were affected only by the processing method. The silages processed by SHR had 3.5% higher DM digestibility and 3.6% higher organic matter digestibility compared to CON (p < 0.01). The biggest differences were found in digestibility of crude fibre and NDF. Total tract NDF and crude fibre digestibilities were higher in SHR than in CON (53.8 vs. 47.9% and 49.4 vs. 43.1%, respectively). Netto Energy of Lactation (NEL), calculated from measured values of chemical composition and digestibility, is presented in Table 3. The NEL values were higher in SHR compared to CON (6.38 vs 6.24 MJ/kg DM, respectively).

4. Discussion

4.1. Chemical Composition and Fermentation Quality of Maize Silages

Inconsistent results regarding differences in nutrient composition between different lengths of cut of maize silages were documented in previous studies. Bal et al. [11] noted that much of the variation in chemical composition of processed maize silages (0.95-, 1.45-, or 1.9-cm theoretical length of cut) can be attributed to more uniform sampling techniques of these types of silages. Differences in plant chemical composition, especially in dry matter content, can occur even within a stand of the same maize hybrid. Significant differences in chemical composition of our silages were found especially between the years, so we assume that the effect of the year of harvest may be a significant factor.

The processing method had no effect on the fermentation profile of silages in our experiment; the differences in these parameters were observed only between the years. Kung and Shaver [18] recommended target levels for pH, ammonia-N content, and lactate content of maize silage of 3.7 to 4.2, 5.0 to 7.0% of CP, and 4.0 to 7.0% of DM, respectively. Kononoff and Heinrichs [6] reported pH, ammonia-N content, and lactate content of maize silage of 3.7, 5.4% of CP, and 5.1% of DM, respectively. Hence, the pH values were comparable with previous studies; the concentrations of lactate and ammonia-N were lower than the recommended concentrations in maize silages. It is that interesting there was a significant decrease in lactic content in the 2nd year, although we did not observe the decrease in pH values.

Some farmers have fears of quality of maize silage processing because the longer chopped material will not be compacted well. We approved in our experiments that SHR method did not influence the quality of fermentation, and therefore, it is not necessary to suspect this.

4.2. Particle Size and Kernel Processing of Maize Silages

The Kernel processing score was higher in the SHR silages than in CON, indicating that, on average, kernel breakage was greater for SHR (difference 12.6%). Additionally, Vanderwerth et al. [19] found a higher processing score of shredlage silage (72.4%) compared to the conventional one (67.6%). These markedly differences were detected also as chopped maize. [20] This indicates better kernel processing and thus higher accessibility in the digestive process.

The SHR treatment led to an increase in the proportion of longer particles in our experiment. The shredlage technology aims at better processing of kernels and at the same time achieving a higher proportion of longer particles. This leads to higher peNDF, which can reduce digestive problems in ruminants. Heinrichs et al. [21] reported that maize silage samples contained 8.1 ± 6.4% of particles greater than 19.0 mm (on DM basis) on average, but the values varied from 1 to 81%.

A higher proportion of longer particles for SHR was expected, because it should be the main reason of this method. However, very important finding is very high differences in kernel processing score for SHR, which could lead to better digestibility for ruminants.

4.3. Total Tract Digestibility

The reported effects of processing on the digestion of maize silage fibre have been variable. Johnson et al. [22] and Schwab et al. [23] reported decreased fibre digestibility due to processing, but Bal et al. [11] reported that processing increased the digestion of fibre from whole maize plant. The positive effect of SHR on NDF in situ disappearance in comparison with CON was also presented [20]. Apparent digestibility of DM and NDF was enhanced by feeding the SHR silages to wethers in our experiment. Maize stalk is crushed as it passes through the kernel processor. This increases the surface area available for the attachment of ruminal microorganisms and thus facilitates digestion. The kernel breakage is the most important factor affecting starch digestibility of maize silages [2] and it is seen also on our results. Cows fed diets with processed maize silages had higher total tract digestion of starch than those fed unprocessed silage in the experiment of Ebling and Kung [24]. Similar to their results, the apparent digestibility of starch and energy, expressed as MJ NEL/kg DM, was enhanced by feeding SHR silage to wethers in this study. The trials by Oba and Allen [25] and Ferrareto et al. [26] reported a decline in feed intake as a result of improved ruminal starch digestibility, without a concomitant decrease in milk yield. The digestibility of starch was also influenced by the year, mainly by amount of starch in maize silages.

5. Conclusions

The shredlage processing of maize plants had significant effect on kernel processing and on peNDF content. The most important finding is a significant effect of shredlage processing on increasing in vivo digestibility of DM, organic matter, starch, crude fibre and NDF, which leads to higher NEL values and thus to an increased nutritional value for ruminants with the potential for higher milk or meat production.