Fatty acid composition of different grassland species
Wyss U. and Collomb M.
Agroscope Liebefeld-Posieux Research Station ALP, 1725 Posieux, Switzerland Corresponding author: ueli.wyss@alp.admin.ch
Abstract
The fatty acids composition of eight grassland species was investigated. Forage of the first growth and the third regrowth (second regrowth for one species) was harvested at three different dates. The samples were freeze-dried and the fatty acids were determined by gas chromatography. The nutrient contents were also analysed. In the grasses and the legumes the sum of the fatty acids, and also the different fatty acids, decreased with age, especially in the forage of the first growth. The highest sums of the fatty acids were detected in the legumes and the herb Taraxacum officinale. The -linolenic acid (C 18:3 c9c12c15) was the most dominant fatty acid. In young plants its proportion was over 60%. An exception was found in T. officinale of the first growth. Here the total fatty acids decreased from the first to the second cutting date and then increased to the third cutting date, because higher amounts of linoleic acid (C 18:2 c9c12) were produced in the older forage.
Keywords: grasses, legumes, cutting date, fatty acids, -linolenic acid, linoleic acid
Introduction
Grasses, legumes and other herbs are an important part of diet of ruminants, and as such, they are an important source of poly-unsaturated fatty acids, despite their low lipid concentration.
Sources of variation in the fatty acid composition are plant species, growth stage, temperature and light intensity (Hawke, 1973). There are several fatty acids in plants, of which the most important are -linolenic acid, linoleic acid and palmitic acid (Bauchart et al., 1984).
The objective of this study was to investigate the influence of different grassland species, which were cut at different dates in the first growth as well as in a regrowth, on fatty acid composition.
Materials and methods
The fatty acid composition of the grasses Lolium multiflorum, Dactylis glomerata, Phleum pratense and Alopecurus pratensis, and the legumes Trifolium repens, Trifolium pratense and Medicago sativa, as well as the herb Taraxacum officinale was investigated. All species were grown in Posieux (altitude 650 m a.s.l.).
Forage of the grasses and the legumes of the first growth and also the third regrowth was harvested at three different dates from the same plot. For Taraxacum officinale forage of the first growth and second regrowth was used. A part of the plots was cut every two weeks to provide forage samples differing in age. The samples were freeze-dried and the fatty acids were determined by gas chromatography (Alves et al., 2008). In addition, a part of the sample was dried at 60 °C, milled, and analysed for crude ash, crude protein, crude fibre and sugar contents.
Results for fatty acid concentrations were analysed by analysis of variance. Correlations between nutrient contents and fatty acid concentrations were calculated.
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Results and discussion
In the first growth, the values of the sum of total fatty acids and of -linolenic acid, linoleic acid and palmitic acid were significant between the different species and cutting dates (Table 1). The highest fatty acid concentrations were found in the young forage of the first growth.
Bauchart et al. (1984) also found the highest fatty acid concentrations in early May.
Furthermore, our results confirm the results of Dewhurst et al. (2001), who found that the age of the forage influences the fatty acids in the forage. The highest values of -linolenic acid were found in legumes, especially in Trifolium repens, and in the herb Taraxacum officinale.
In young plants their proportion was over 60%. An exception was T. officinale. Here the total fatty acids decreased from the first to the second cutting date and then increased to the third cutting date of the first growth, because high amounts of linoleic acid were produced in the older forage. It is supposed that the white sap in the T. officinale is responsible for this development.
In the third regrowth (second regrowth for T. officinale), the fatty acid composition between the different species and cutting dates also differed (Table 2). As expected, the contents of the regrowths were not higher than in the first growth. According to Van Rast et al. (2009) plants in the generative stage have higher FA concentration than in the reproductive stage.
Table 1. Fatty acid concentrations in dry matter of eight species and three cutting dates of the first growth (g kg-1)
Species Cutting date C16:0 C18:2 c9,c12 C18:3 c9c12c15 Sum of fatty acids
Lolium multiflorum 28.04. 3.4 3.1 17.0 28.0
12.05. 3.1 3.1 11.8 21.8 26.05. 2.6 2.9 6.7 15.1
Dactylis glomerata 28.04. 3.9 4.6 20.4 34.5
12.05. 3.0 3.8 12.3 22.9 26.05. 2.5 3.2 9.0 18.4
Phleum pratense 28.04. 3.7 5.1 17.7 31.9
12.05. 3.0 4.3 11.4 23.1 26.05. 2.4 3.3 7.7 17.5
Alopecurus pratensis 28.04. 3.9 5.8 18.8 34.1
12.05. 2.9 4.3 11.8 23.0 26.05. 2.4 5.0 7.5 19.0
Trifolium repens 28.04. 5.6 7.3 27.6 48.0
12.05. 5.1 6.3 24.6 43.7 26.05. 4.9 6.1 19.4 37.4
Trifolium pratense 28.04. 4.7 7.1 21.0 38.9
12.05. 4.1 5.9 16.2 31.7 26.05. 3.5 4.9 12.6 25.5
Medicago sativa 28.04. 5.3 6.9 19.7 37.7
12.05. 4.6 5.8 15.9 31.5 26.05. 3.8 4.7 11.6 24.4
Taraxacum officinale 15.04. 5.4 7.8 22.7 42.2
28.04. 5.1 7.9 14.7 33.0 12.05. 5.8 23.7 8.8 50.0
Species (S) *** *** *** ***
Cutting date (D) *** *** *** ***
Interaction SxD *** *** *** ***
*** P < 0.001
The crude fibre content correlated negatively with the sum of the fatty acids (r= -0.76), C16:0 (r= -0.75), C18:2 (r= -0.40) and C18:3 (r= -0.71). In contrast, the crude protein content and the sum of the fatty acids (r= 0.78), C16:0 (r= 0.74), C18:2 (r= 0.23) and C18:3 (r= 0.86) correlated positively.
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Table 2. Fatty acid concentrations in dry matter of eight species and three cutting dates of the third regrowth respectively second regrowth for T. officinale (g kg-1)
Species Cutting date C16:0 C18:2 c9,c12 C18:3 c9c12c15 Sum of fatty acids
Lolium multiflorum 24.08. 3.3 3.9 13.9 25.8
07.09. 2.9 3.6 11.0 21.9 21.09. 3.7 4.3 11.4 26.2
Dactylis glomerata 24.08. 3.3 3.7 16.2 29.2
07.09. 2.6 3.1 11.5 22.0 21.09. 2.6 3.8 11.9 22.9
Phleum pratense 24.08. 3.3 4.5 13.6 28.4
07.09. 2.7 4.4 10.6 24.5 21.09. 2.7 4.0 10.6 24.7
Alopecurus pratensis 24.08. 2.9 4.1 12.7 25.3
07.09. 2.8 3.9 13.2 24.6 21.09. 2.9 3.5 12.6 24.5
Trifolium repens 24.08. 4.7 5.9 21.6 39.8
07.09. 4.1 5.9 19.7 36.9 21.09. 3.9 5.8 17.4 34.4
Trifolium pratense 24.08. 3.7 5.7 14.0 28.9
07.09. 3.2 5.1 12.6 26.4 21.09. 2.9 5.0 10.9 24.3
Medicago sativa 24.08. 4.5 5.2 17.0 32.6
07.09. 3.9 4.8 15.4 29.6 21.09. 3.6 4.6 15.0 28.4
Taraxacum officinale 24.06 4.9 7.1 21.1 39.2
08.07. 4.6 6.2 17.5 33.6 22.07. 4.3 6.0 14.9 30.1 Species (S) *** *** *** ***
Cutting date (D) *** *** *** ***
Interaction SxD *** *** *** ***
*** P < 0.001
Conclusions
xThe fatty acid concentrations differ between plant species. Legumes, especially Trifolium repens, have more fatty acids than grasses.
xAn important factor for the fatty acid composition is the age of the forage.
x-linolenic acid is the dominant fatty acid in grass.
xAn exception was T. officinale. For this species, high amounts of linoleic acid were produced in the older forage of the first growth.
References
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Bauchart D., Verite R. and Remond B. (1984) Long-chain fatty acid digestion in lactating cows fed fresh grass from spring to autumn. Canadian Journal of Animal Science 64 (Suppl.), 330-331.
Dewhurst R.J., Scollan N.D., Youell S.J., Tweed J.K.S. and Humphreys M.O. (2001) Influence of species, cutting date and cutting interval on the fatty acid composition of grasses. Grass and Forage Science 56, 68-74.
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