• Keine Ergebnisse gefunden

Variation of fatty acid content in grass and milk during the grazing season

N/A
N/A
Protected

Academic year: 2022

Aktie "Variation of fatty acid content in grass and milk during the grazing season"

Copied!
4
0
0

Wird geladen.... (Jetzt Volltext ansehen)

Volltext

(1)

Variation of fatty acid content in grass and milk during the grazing season

Wyss U., Münger A. and Collomb M.

Agroscope Liebefeld-Posieux Research Station ALP, Posieux, Switzerland Corresponding author: ueli.wyss@alp.admin.ch

Abstract

Fatty acid composition in grass varies during the growth season. Grass fed to dairy cows may yield corresponding changes in milk fatty acid content. To investigate this, monthly individual milk samples of 16 (2005) and 20 cows (2007) and corresponding grass samples were analysed throughout the grazing season. The cows were grazing full time in a rotational system on a mixed sward. As supplements, the cows were offered carbohydrate-type concentrate restrictively according to their milk production. In spring and autumn, the grass had lower crude fibre and higher crude protein contents than in summer. -linolenic acid (C18:3) was the most important fatty acid in the grass. With higher crude fibre contents, the grass had less -linolenic acid. In 2005, conjugated linoleic acid (CLA) concentration in milk was higher in spring and in autumn than in summer. In 2007, CLA increased continuously from spring to autumn. In both years, the mean CLA content was 1.5 g per 100 g fat. The concentration of omega-3 fatty acids did not vary much during the pasture season in 2005. In 2007, the omega-3 increased during the grazing season. The average content was 1.4 g per 100 g fat.

Keywords: grazing, milk, fatty acid content, CLA, omega-3

Introduction

Fatty acid content varies in forages during the grazing season. Their composition depends on different factors such as plant species, development stage, temperature, and light intensity (Hawke, 1973). Differences in feed fatty acid composition also influence the concentrations of fatty acids in milk (Schroeder et al., 2004). Furthermore, grazing alone is often not sufficient to meet total nutritional requirements in high producing lactating dairy cows (Delaby et al., 2003). Consequently, different types of concentrates are often supplemented in order to prevent energy, protein, mineral, and vitamin deficiencies as well as to enhance milk yield. The objective of this study was to compare feed and milk fatty acid profiles of cows over the grazing season in two different years.

Materials and methods

The experiments were conducted from April to November in both 2005 and 2007 in Posieux (altitude 650 m a.s.l.; average annual rainfall: 1014 mm). The cows were grazing full time in a rotational system on a mixed sward composed of 78% grasses (mainly ryegrass), 13% clover and 9% other herbs. In spring and autumn, the diet was supplemented in-barn with conserved forage. In 2005, 16 dairy cows were allotted to two groups. The two groups received concentrate supplements that differed by their carbohydrate composition. They consisted either of a starchy concentrate (corn-barley) or a highly digestible fibre concentrate (beet pulp) offered at variable levels during the trial according to milk production: 0.5 kg per kg of milk production above 24 kg per day with a maximum of 6.5 kg of concentrate. The fat content of the concentrates amounted 35 and 10 g kg-1 in dry matter (DM). In August 2005, due to drought conditions occurring in the region, maize silage was added to the diet in both groups of cows during several weeks.

Grassland Science in Europe, Vol. 15 422

(2)

In 2007, 20 cows were assigned to two groups. One group was offered concentrate (corn- barley) according to their actual milk production as in 2005. The other group received the same concentrate but at a fixed amount of 3.5 kg d-1 during the first 150 days of lactation.

During the grazing season, grass samples were collected to determine the nutrient contents as well as the fatty acid composition. The milk yield and the intake of concentrate were registered daily. Every month, a milk sample of every cow was taken and the fatty acid composition in the milk fat was analysed. The milk fat composition was analysed according to Collomb and Bühler (2000).

Results and discussion

In spring and autumn of both years, the grass had higher crude protein and lower crude fibre contents than in summer (Fig. 1). The fatty acid concentrations of the grass, especially the - linolenic acid, were lower in summer (Fig. 2). The -linolenic acid was the most important fatty acid in the grass, varying between 59 and 73% of the sum of the fatty acids. The correlation between the crude fibre content and the sum of the fatty acids was -0.60 and with -linolenic acid -0.63; with other fatty acids, theses correlations were lower being -0.49 for C16:0, -0.05 for C18:0, -0.10 for C18:1 and -0.43 for C18:2.

Figure 1. Crude fibre content in the grass Figure 2. -linolenic acid (C18:3) and sum of the fatty acids in the grass

In both years, the daily milk production per cow decreased during the grazing season. At the end of the season in 2005, the milk production increased again because 7 of the 16 cows were replaced by cows at the beginning of lactation (Fig. 3). The decreasing milk production during the season resulted in less concentrates being offered. In 2005, the average quantity of concentrate per day decreased from 5.0 to 2.7 kg. In 2007, the two groups received respectively 4.5 and 3.5 kg of concentrate per day at the beginning of the trial but no concentrates were given at the end of the trial. The average milk fat contents varied between 33 and 44 g kg-1 (Fig. 4).

In 2005 and 2007, the milk fat contained respectively 57.5 and 56.6 g saturated fatty acids per 100 g fat, 25.0 and 26.6 g mono-unsaturated fatty

acids per 100 g fat, and 4.8 and 4.9 g poly-unsaturated fatty acids per 100 g fat. In 2005, the concentration of conjugated linoleic acid (CLA) in milk was higher in spring and in autumn than in summer. In 2007, CLA increased continuously from spring to autumn (Figure 5). In both years, the mean CLA content was 1.5 g per 100 g fat.

The variation of the CLA during the grazing season in 2007 was similar to the results obtained by Collomb et al. (2008) in milk from mountain regions in Switzerland as well as to results from a pasture-based system with low concentrate supplementation (Wyss et al., 2010). The different concentrate types in trial 2005, starchy or containing highly digestible fibre, had no significant influence on the concentrations of total CLA. The content of omega-3

Grassland in a Changing World 423

(3)

fatty acids did not vary much during the pasture season in 2005. In 2007, the omega-3 increased during the grazing season (Figure 6). The mean content was 1.4 g per 100 g fat.

Figure 3. Average milk production over the grazing season

Figure 4. Mean milk fat content

Figure 5. Concentration of CLA in milk fat Figure 6. Omega-3 fatty acids in milk fat

Conclusions

x The fatty acid content in grass, especially the -linolenic acid, varies during the grazing season. In young grass (lower crude fibre content), the fatty acid content is higher than in older grass.

x Milk from the pasture has high amounts of CLA and omega-3 fatty acids.

x CLA and partly omega-3 fatty acids vary during the grazing season. This can be partly explained by the variations of the fatty acid contents of the forage.

References

Collomb M. and Bühler T. (2000) Analyse de la composition en acides gras de la graisse de lait. I. Optimisation et validation d’une méthode générale à haute résolution. Mitteilungen aus Lebensmitteluntersuchung und Hygiene 91, 306-332.

Collomb M., Bisig W., Bütikofer U., Sieber R., Bregy M. and Etter L. (2008) Seasonal variation in the fatty acid composition of milk supplied to dairies in the mountain regions of Switzerland. Dairy Science Technology 88, 631-647.

Delaby L., Peyraud J.L. and Delagarde R. (2003) Faut-il complémenter les vaches laitières au pâturage? INRA Productions Animales 16, 183-195.

Hawke J.C (1973) Lipids. In: Butler G.W. and Bailey R.W. (eds.) Chemistry and Biochemistry of Herbage.

London Academic Press, pp. 213-263.

Schroeder G.F., Gagliostro G.A., Bargo F., Delahoy J.E. and Muller L.D. (2004) Effects of fat supplementation on milk production and composition by dairy cows on pasture: A review. Livestock Science 86, 1-18.

Wyss U., Collomb M., Frey H.J. and Hofstetter P. (2010) Seasonal variation in fatty acid contents of cow milk from indoor and a pasture-based feeding. Grassland Science in Europe 15 (this volume).

Grassland Science in Europe, Vol. 15 424

(4)

Effect of pasture botanical composition on milk composition in organic production

Adler S.1,2, Dahl A.V.3,Vae A.H.2, Thuen E.2, Garmo T.2, Krogh-Jensen S.4, Hansen-Møller J.4 and Steinshamn H.1

1Bioforsk Organic Food and Farming Division, N-6630 Tingvoll, Norway

2Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, N- 1432 Ås, Norway

3Nofima Food, N-1432 Ås, Norway

4Faculty of Agricultural Sciences, Aarhus University, DK-8830Tjele, Denmark Corresponding author: steffen.adler@bioforsk.no

Abstract

Milk samples from sixteen Norwegian Red dairy cows grazing mixed swards of either grass- red clover (GR) or mixed swards of sown and unsown species of grass, clover and other herbs (GCH) were collected during four periods. Both pastures were organically managed. Pasture botanical composition had no effect on milk fat, protein or vitamin concentration and only minor effects on fatty acid composition. Milk from GR had higher concentrations of the phytoestrogens equol, genistein and biochanin A than the milk from GCH. Concentrations of equol in milk from GR were higher than concentrations reported from experiments with red clover silage. The oxidative stability of the milk lipids was not affected by pasture type.

Keywords: Dairy production, grazing, botanical composition, fatty acids, vitamins, phytoestrogens, oxidative stability

Introduction

Forages with high proportions of legumes tend to increase the proportion of polyunsaturated fatty acids (PUFA) in milk fat (Dewhurst et al., 2003). Red clover (Trifolium pratense L.)- grass silage also increases the milk proportion of PUFA, in particular -linolenic acid (ALA), compared to white clover (Trifolium repens L.)-grass silage (Steinshamn and Thuen, 2008).

However, increased proportion of PUFA in milk fat may increase the susceptibility of milk lipids to photo-oxidation (Havemose et al., 2004). Red clover has also shown to yield high concentrations of phytoestrogens in milk (Mustonen et al., 2009). The aim of this study was to examine if milk composition of fatty acids (FA), vitamins and phytoestrogens, and the susceptibility of milk to photo-oxidation are affected by pasture botanical composition.

Material and methods

A continuous grazing experiment was conducted in Ås, Norway, with sixteen Norwegian Red dairy cows (80 ± 15.0 days in milk (d.i.m.)) with three 3-week periods of measurements: in June, July and September 2008. The cows were blocked by genetic line, d.i.m. and milk yield and were allocated randomly to the two treatments: a grass-red clover pasture (GR) in the first production year, and a five-year-old pasture including sown and unsown species of grass, clover and other herbs (GCH) with a daily dry matter (DM) allowance of approximately 20 kg cow-1 d-1and supplemented with 3.0 kg d-1 of barley pellets, including minerals. Both pastures were organically managed. A period with indoor silage feeding before grazing was used as a baseline period. Both groups were grazing together between the three3-periods on pastures similar to GCH. GR contained 54% grasses, 28% red clover, 1% white clover and 17% other herbs, and GCH contained 66% grasses, 3% red clover, 21% white clover and 10% other

Grassland in a Changing World 425

Referenzen

ÄHNLICHE DOKUMENTE

The influence of the botanical composition of grass on milk composition has been studied in the lowlands (altitude 600-650 m), mountains (900-1200 m) and highlands (1275-2120

Conjugated linoleic acid and trans fatty acid composition of cow's milk fat produced in lowlands and

The amount of CLA in the Swiss cooked sausages ranges from 22.1 (Lyoner from poultry) to 78.9 mg (frying sausage from veal) per 100 g sausage (Tab. The CLA content of frying

Correlation coefficients have been calculated between the occurrence of plant families and species and the concentrations of groups of fatty acids in milk fats from the Mountains

The aim of the current study is to determine once more the fatty acid composition of milk fat in the 44 milk samples from the three vegetation sites in Switzerland using a

In the current study the de- creased percentage of hay and concentrates combined with the increased percentages of fresh grass with increasing fractions of GBF, as well as

Despite the higher α-linolenic acid intake, the concentration of this important n-3 FA in milk fat decreased significantly (-8.0%) when hay was supplemented with grass

This study compared the impact on the fatty acid (FA) composition of milk fat of traditional summer grass-feeding in the Lowlands (600-650 m), Mountains (900-1210 m) and Highlands