Grassland – a European Resource? 323 Influence of conservation method on fatty acid composition of herbages of a permanent grassland meadow
Wyss U.
Agroscope Liebefeld-Posieux Research Station ALP-Haras, 1725 Posieux, Switzerland Corresponding author: ueli.wyss@alp.admin.ch
Abstract
The main sources of variation in the fatty acid composition of fresh herbage are plant species, growth stage, temperature and light intensity. The conservation method can also influence the fatty acid composition. In an experiment, the fatty acids composition of fresh grass, three silages with dry matter contents of 20, 35 and 50%, and of barn-dried and field-dried hay were investigated. Samples were taken at harvest and after a storage period of 115 days. The samples were freeze-dried and the fatty acids were determined by gas chromatography. In addition, the nutrient contents were analysed.
With increasing amounts of pre-wilting, the individual and total fatty acids, such as α-linolenic and linoleic acid, decreased, which is due to leaf shatter and oxidative losses.
Differences were also found after the storage period. For the three different silages, the concentration of different fatty acids increased during the storage period. The silage with the lowest dry matter content had the highest fermentation intensity, the highest sugar degrada- tion and the highest concentration of fatty acids. Conservation as hay caused fewer changes with respect to fatty acids before and after the storage period.
Keywords: silages, hay, fatty acids, linolenic acid, linoleic acid Introduction
Wilting forages for the production of hay, and to a lesser extent prior to ensiling, decreases fatty acid concentration due to oxidative losses and leaf shatter (Dewhurst et al., 2006). As the leaves contain higher concentrations of fat and fatty acids than the stems (Wyss, 2012), the leaf shatter contributes to the loss of fatty acids during the drying period in the field.
The objective of this study was to investigate the fatty acid concentration during the process of silage and hay making, both in the field and during the storage period.
Materials and methods
The fatty acids composition of fresh grass, three silages with dry matter contents of 20, 35 and 50%, and of barn-dried and field-dried hay were investigated. All forages were produced in Posieux (altitude 650 m a.s.l.). The forage was a third cut from a permanent meadow. It consisted of 73% grasses (mainly ryegrass), 9% legumes and 18% herbs. The silages were ensiled in laboratory silos of a capacity of 1.5 l. For the barn-dried hay, samples of 4 kg were put in nets and the nets were put in the forage of a conventional barn drying system.
For the field-dried hay, the hay was stored in a wooden box in a dry place. There were three replications of all variants.
Samples were taken during the harvest process in the field and after a storage period of 115 days. The samples were freeze-dried and the fatty acids were determined by gas chroma- tography (Alves et al., 2008). In addition, a part of the samples were dried at 60°C, milled, and the crude ash, crude protein, crude fibre and sugar contents were analysed. The data were analysed with SYSTAT 12 using one-way ANOVA.
324 Grassland Science in Europe, Vol. 17 Results and discussion
The crude protein content tended to decrease with increasing amounts of pre-wilting (Ta- ble 1). For the fibre contents (ADF and NDF) there was no direct influence of the extent of wilting. The silages with 35 and 50% DM had a good fermentation quality, but the silage with 20% DM contained butyric acid.
Table 1. Dry matter (DM) – and nutrient contents of the silages and the hays (g kg–1 DM)
DM Ash CP ADF NDF pH
Silage 20% DM 197 130 158 311 470 4.5
Silage 35% DM 373 135 150 287 441 4.8
Silage 50% DM 519 115 160 299 486 6.1
Barn dried hay 904 98 134 274 473 –
Field dried hay 884 95 134 283 502 –
SEM 1.9 0.5 1.1 1.4 5.6 0.01
Significance *** *** *** *** *** ***
SEM standard error of mean; * P < 0.05; ** P < 0.01; *** P < 0.001; ns – non significant.
More extensive wilting generally reduced individual fatty acids and total fatty acids (TFA) (Table 2). These changes are due primarily to leaf shatter losses; high reductions of the different fatty acids during the wilting-process were also found by Dewhurst et al. (2006) and Shingfield et al. (2005). The α-linolenic acid (C 18:3 c9c12c15) was the most dominant fatty acid. Their proportion in the total fatty acids (TFA) decreased from 58% to 50% with more extensive wilting. The linoleic (C18:2 c9,c12) and palmitic acid (C16:0) had proportionally a decline of between 12 and 16%.
Table 2. Fatty acid concentrations in the different forage prior to storage (g kg–1 DM)
Variants C16:0 C16:1
t3 C18:0 C18:1
c9 C18:2
c9c12 C18:3
c9c12c15 TFA
Fresh grass 4.4 0.6 0.4 0.6 4.4 19.8 34.3
Grass 20% DM 4.5 0.5 0.3 0.7 4.8 18.9 33.9
Grass 35% DM 4.4 0.6 0.4 0.7 4.2 17.2 31.6
Grass 50% DM 4.2 0.5 0.3 0.6 3.8 15.1 28.7
Grass 80% DM 4.0 0.4 0.3 0.5 4.1 12.8 25.7
Grass 88% DM 4.1 0.5 0.3 0.5 3.5 13.4 25.8
SEM 0.09 0.04 0.01 0.03 0.21 0.74 1.04
Significance * ns ns *** * *** ***
SEM standard error of mean; * P < 0.05; ** P < 0.01; *** P < 0.001; ns – non significant.
Table 3. Fatty acid concentrations in the different forage after storage period (g kg–1 DM)
Variants C16:0 C16:1
t3 C18:0 C18:1
c9 C18:2
c9c12 C18:3
c9c12c15 TFA
Silage 20% DM 4.8 0.6 0.4 0.7 5.2 21.1 37.7
Silage 35% DM 4.6 0.6 0.4 0.7 4.8 19.5 34.9
Silage 50% DM 4.5 0.5 0.4 0.6 4.5 17.3 32.1
Barn dried hay 4.1 0.5 0.3 0.5 3.9 14.3 27.1
Field dried hay 3.9 0.5 0.3 0.5 3.7 14.0 26.8
SEM 0.12 0.02 0.01 0.01 0.16 0.63 1.20
Significance ** ** *** *** *** *** ***
SEM standard error of mean; * P < 0.05; ** P < 0.01; *** P < 0.001; ns – non significant.
The fatty acid concentrations in the different forage after the storage period are shown in Table 3. The concentrations of individual and total fatty acids were higher in the silages than in the
Grassland – a European Resource? 325 wilted grass at ensiling. The silage with the lowest dry matter content had the highest fer- mentation intensity, the highest sugar degradation and the highest concentration of individual and total fatty acids. According to Boufaied et al. (2003) silage had higher concentrations of C16:0, C18:2, C18:3 and TFA than fresh grass. For the two hay variants, the values after the field and after the storage period were more similar in comparison to the silage variants.
Figure 1 shows the strong relation between the DM-contents and the total fatty acids (TFA) after the field and storage period.
Conclusions
The degree of pre-wilting strongly influenced the individual and total fatty acids in the for- age. In the silages the individual and total fatty acids increased during the storage period.
In the hay variants there were fewer changes concerning the fatty acids found during the storage period.
References
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Figure 1. Relation between the DM-contents and the total fatty acids (TFA) after the field and storage period