Evaluation of the chemical composition and the
particle size of maize silages produced
in north-west of Portugal
A.J.M. Fonseca
a,*, A.R.J. Cabrita
b, A.M. Lage
c, E. Gomes
a aInstituto de CieÃncias BiomeÂdicas de Abel Salazar, University of Porto, Campus AgraÂrio de VairaÄo,Rua do Monte, Crasto ± VairaÄo, 4480 Vila do Conde, Portugal
bLaboratoÂrio de AnaÂlise de Alimentos AGROS-UP, Campus AgraÂrio de VairaÄo, Rua do Monte,
Crasto ± VairaÄo, 4480 Vila do Conde, Portugal
cFaculdade de CieÃncias, University of Porto, Campus AgraÂrio de VairaÄo, Rua do Monte,
Crasto ± VairaÄo, 4480 Vila do Conde, Portugal
Received 30 June 1999; received in revised form 30 June 1999; accepted 16 December 1999
Abstract
The chemical composition and the particle size distribution of 37 maize silages produced in north-west of Portugal were determined. Mean dry matter (DM), crude protein (CP), neutral detergent ®bre (NDF) and starch were 28833, 819, 50245 and 22954 g kgÿ1 DM,
respectively. Particle size was determined by manual separation of fresh silage into three fractions: material >30 mm in length; material between 30 and 10 mm in length; and material <10 mm in length. Linear interpolation and extrapolation calculated median particle size. The effects of chopping±harvesting machine type and percentage of blades used to chop maize plants were also analysed.
The results of this study suggested that most farmers chopped the maize plants very coarsely prior to storage. In fact, the type of chopping±harvesting machine had no effect on median particle size, but the percentage of blades used affected signi®cantly (p<0.001) this parameter. This can prevent maximisation of voluntary intake and high milk yields. Therefore, extension work is necessary to implement the ®ne chop of maize plants and to correctly choose as well harvest date and the maize varieties that are most adapted to local production conditions.#2000 Published by Elsevier Science B.V. All rights reserved.
Keywords:Particle size; Chemical composition; Maize silage 83 (2000) 173±183
*Corresponding author. Tel.:351-52-662399; fax:351-52-661780.
E-mail address: [email protected] (A.J.M. Fonseca).
1. Introduction
In recent years milk production in Portugal has increased, particularly in the north and central region near the cost. The decrease in the number of dairy farms, the increase in number of cows per farm and, more recently, the widespread use of totally mixed ration feeding systems are the most evident changes in dairy production.
Although formulating properly balanced rations ®rst requires an accurate assessment of forage composition, particularly of maize silage, which is a main forage for dairy cows in Portugal, de®nition of the physical form is also important (Mertens, 1997). When cows ingest insuf®cient forages with an adequate particle length for proper rumination activity, this may reduce dry matter (DM) and energy intake, whole tract DM digestibility, milk and fat production, and result in health problems like acidosis, laminitis, abomasum disorders and ketosis (Sudweeks et al., 1981). Numerous studies have shown that a reduction in particle size leads to a reduction in chewing activity and milk fat content (Campling and Freer, 1966; Woodford et al., 1986; Woodford and Murphy, 1988; Grant et al., 1990a, b; De Boever et al., 1993). Allen (1997) reviewed the purported requirement for physically effective (pe) ®bre (peNDF) of high producing dairy cows and concluded that forage has a critical mean particle size, above which additional length adds little bene®t. Clark and Armentano (1999) showed that an increase in the forage content in the diet above a basal amount, in a low ®bre control diet with 12% neutral detergent ®bre (NDF) from hay crop forage, with both hay crop or corn silage increased rumination and total chewing time. However, these authors did not ®nd differences in physical effectiveness between coarse chop corn silage, ®ne chop corn silage or an equal mixture of the two.
Reduced forage particle size increases both DM intake (Jaster and Murphy, 1983; Martz and Belyea, 1986; UdeÂn, 1988) and microbial protein synthesis (Rode et al., 1985; UdeÂn, 1988) because of the increased rumen out¯ow rate. In addition, maize ensiling requires the short chopping of the maize plants to facilitate packing in the silo and to assure that most kernels will be crushed. When coarsely cut, maize silage is more likely to develop mould growth and there is also the risk that more kernels will be lost in faeces (Raymond et al., 1986).
The information available on this topic in our country is very scarce. Therefore, this project was implemented with the objective to evaluate the chemical composition and the particle size distribution of maize silage from local farms.
2. Materials and methods
2.1. Maize silages
Individual samples of maize silage from 37 local dairy farms were collected for analysis chemical composition and particle size. The silages were from unknown varieties but were all grown and ensiled in 1998. A survey was also conducted to assess the type of chopping±harvesting machine and number of blades used to chop the maize plants prior to storage. This latter is important, because it is a common practice to remove some blades to increase the work capacity.
2.2. Particle size analysis
Particle size was determined by manual separation on a glass table with a quadricular (10 mm) sheet. The maize silage samples were divided into three fractions: material >30 mm in length; material between 30 and 10 mm in length; and material <10 mm in length. Whole maize grains when greater than 10 mm were included in material between 30 and 10 mm in length. Subsamples (100 g) of each sample were analysed three times.
The material from each fraction was weighed and then dried in a forced-air oven at 658C for 48 h. The percentages of particles were calculated on a fresh and a DM basis. Subsamples of dried material were bulked by fraction length of particles for later chemical analysis.
2.3. Chemical analysis
Samples of silages were dried in a forced-air oven at 658C for 48 h and the DM content calculated. Ground samples (1 mm screen) were analysed for ash and Kjeldahl nitrogen according to the AOAC (1990). Neutral detergent ®bre (NDF) was determined as described by Robertson and Van Soest (1981). Ether extract (EE) was determined by extracting the sample with petroleum ether using a Gerhardt Soxtec System. Starch was measured on ground samples (0.5 mm) as described by Solomonsson et al. (1984). pH was determined in fresh samples with a pH electrode.
2.4. Statistical analysis
At-comparison test was used to analyse the percentages of particles on a fresh and a DM basis (Steel and Torrie, 1980). Linear interpolation and extrapolation to the size of which 50% of the material was divided calculated median particle size of samples. Median particle size data were submitted to an ANOVA with two factors, the type of ensiling machine and the percentage of blades used (Steel and Torrie, 1980). The relationships between different characteristics of silages were obtained by simple linear regression analysis (Steel and Torrie, 1980).
3. Results and discussion
3.1. Chemical composition
Sensorial evaluation suggested that all silages were well preserved, which was con®rmed by pH values (Table 1), since for only one silage the pH was higher than 4 (Demarquilly, 1994). The low ash values indicated that silage contamination with soil was modest. DM content varied from 231 to 394 g kgÿ1, NDF ranged between 368 and 591 g kgÿ1DM and starch between 126 and 349 g kgÿ1DM.
The large range in DM content, observed in 1 year, suggests a big variation in harvest date and in maturity type of the maize. Raymond et al. (1986) showed that within the
range of 25±35%, an increase in the DM content of maize silage by 5 percentage units resulted in a higher grain content of an average 5.7% and in a better live weight gain of steers 4%. However, the increase in animal productivity was, essentially, a consequence of a higher intake, since the feed conversion ef®ciency was unchanged. Demarquilly (1994) also reported that DM intake of maize silage by cattle increased with DM content up to35%.
Table 1
Chemical composition of the maize silages Silage DM
Starch content was, as expected, negatively correlated with NDF (rÿ0.609,p<0.001) and positively correlated (r0.363, p<0.05) with DM content (Fig. 1). Although DM content of silage accounted only for 13% of the variation observed, this relationship show that higher DM silages are generally richer in grain although other factors, such as cultivar are clearly important (BarrieÁre et al., 1995; Johnson et al., 1997). In the present study, both maize varieties and production conditions are different and unknown, which may help to explain the lower correlation found. Thus, a deliberate choice of the maize hybrid and of the stage of maturity might improve the contribution of forage for covering the total nutrient requirements of animals.
3.2. Particle size
The data of particle size distribution of the individual samples are presented in Table 2. The low standard deviation within subsamples demonstrates that the method used to separate particles of silage, although laborious, has reasonable repeatability. The results on a fresh basis differed signi®cantly (p<0.05) from those on a DM basis, particularly for particles <10 mm. This can be explained by a difference in DM content among the fractions.
Demarquilly (1994) reported that the ideal particle size distribution of maize silage for dairy cow is: 1% of material >20 mm; 9% of material between 20 and 10 mm; 45% of material between 10 and 6 mm and 45% of material <6 mm. Clark and Armentano (1999) suggested that coarse and ®ne maize silages are those which have mean particle sizes of 8.74 and 4.14 mm, respectively. Compared to these guidelines, our data suggest that most farmers chopped the maize plants very coarsely (Table 3), since only 9 of the 37 silages studied had a median particle size <10 mm. This is probably the result of removal of some blades of the chopping±harvesting machines to increase the speed of harvest (Table 3). In
Fig. 1. Relationship between starch and dry mater content (DM) of maize silages.
fact, the results of ANOVA show that while the type of chopping±harvesting machine had no effect (p>0.05) on median particle size, the percentage of blades used affected (p<0.001) this parameter (Table 4). When all blades were used, the median particle size of maize silages was 9.9 mm.
Table 2
Means, standard deviations, andt-test comparison of the percentage of particles that were <10 and 30 mm calculated on a fresh and dry matter (DM) basis
Fresh silage Dry silage p
Chase (1995) stated that for high feed intakes to be achieved in dairy cows, higher energy diets with levels of starch between 25 and 30% (DM basis) must be used during the period of greatest energy requirements. De Brabander et al. (1990) reported that voluntary intake by dairy cows was higher with normally chopped maize silage (5 mm) compared with that insuf®ciently chopped (16 mm). Maize silages ®nely chopped and
Table 3
Type of chopping±harvesting machine, percentage of blades used and means and standard deviations of median particle size of maize silages on a dry matter (DM) basis (mm)
Silage Machine Blades (%) Median (mm; DM basis)
X SD
with high DM and starch contents are important feeds to achieving these objectives. Thus, the tradition of removing blades is a real obstacle to achieving higher intakes and higher milk yields in this region.
Another problem of coarsely chopped maize plants, particularly with higher DM content silages, is the percentage of grains that are not broken, since the faecal grain losses may increase (Demarquilly et al., 1995). The percentage of total starch and NDF recovered in the fraction of material between 30 and 10 mm in length is important (Table 5). There is also a negative and signi®cant (p<0.001) linear relationship between median particle size and the percentage of total starch recovered in fraction of material <10 mm (Fig. 2). Knowlton et al. (1998) studied the effects of grinding or rolling high moisture or dry corn grain on the performances of dairy cows in early lactation and found only an improvement with the former treatment.
In this study, we used median particle size calculated by linear interpolation or extrapolation to describe differences between silages. This method has, according to Murphy and Zhu (1997), the advantages of avoiding the assumption of an underlying
Table 4
Effects of chopping±harvesting machine type and percentage of blades used on median particle size of maize silages on a dry matter (DM) basis (mm)
Chopping±harvesting machine Blades (%) F-test
1 2 3 4 5 6 50 67 100 Machine Blades (%) Median 10.9 12.0 11.8 12.8 13.6 15.4 15.0 13.4 9.9 0.254 0.001 SEMa 0.7 1.3 1.7 1.7 2.0 2.0 0.7 1.7 1.1
aStandard error of mean.
Fig. 2. Relationship between percentage of total starch in particles <10 mm and median particle size of maize silages on a dry matter (DM) basis.
particle size distribution, since there is not agreement about the mathematical form that such distribution follows and bias is not introduced by the use of different fraction particle lengths. However, because the distribution of particle size is important, Lammers et al. (1996) reported that a line describing the distribution is more useful and thorough than a simple statement of ®nding the mean particle size.
Table 5
Percentage of total starch and total neutral detergent ®bre (NDF) on particles that were <10 and 30 mm
Silage <10 mm <30 mm
4. Conclusion
This study demonstrates that very coarsely chopped maize silages predominate in north and central Portugal. This can prevent maximisation of voluntary intake and high milk yields. Therefore, extension work is necessary to implement the ®ne chop of maize plants and to correctly choose as well harvest date and the maize varieties that are most adapted to local production conditions.
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