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Doctoral thesis, 2009

Factors affecting fatty acid composition in forage and milk

Arvidsson, Katarina

Abstract

The aims of the studies underlying this thesis were to evaluate variations in fatty acid (FA) contents of plants used as forage for dairy cows in northern Sweden, and their effects on the FA contents of the milk. Initially, samples of timothy (Phleum pratense L.) were subjected to different pre-treatments prior to analysis. Freezing with liquid N was not necessary to obtain apparently reliable FA profiles of the samples examined. The prevailing method for handling samples before analysis, i.e. freeze-drying and grinding, was satisfactory. However, heat drying samples at 60°C was just as good, or even better in some cases. Neither wilting (to 330-350 g dry matter/kg) nor application of additives (acid additive or bacterial inoculant) to timothy had any substantial effects on the proportions of FAs in silage. In addition, seasonal variations in FA concentrations were evaluated in timothy and meadow fescue (Festuca pratensis Huds.) subjected to three different N fertilization regimes and harvested at different stages of maturity during their spring and summer growth periods. FA concentrations in both grasses declined over time in both growth periods. There were positive linear relationships between FAs and concentrations of crude protein (CP) and crude fat, which might be useful as tools to predict FA concentrations in the forage. Furthermore, the two grass species examined showed differences in FA profiles, notably timothy had higher concentrations of C18:2 n-6 and meadow fescue higher concentrations of C18:3 n-3, but the total fatty acid concentrations were similar in both grasses. In addition, three timothy silages subjected to different N-fertilization regimes and a red clover/timothy silage (60:40 on DM basis) were fed to 24 dairy cows in a change-over design. Higher levels of N-fertilization led to higher concentrations of CP accompanied by higher concentrations of FAs in silage. However, these differences did not affect the concentrations of either protein or 18:3n-3 in the milk of cows fed these grass silages, but including red clover in the cows’ diet led to increased concentrations of C18:3 n-3 and cis-9, trans-11 18:2 in their milk.

Keywords

Fatty acids, Festuca pratensis Huds., Milk production, Pre-treatments, N-fertilization, Phleum pretense L., Seasonal variation, Silage, Trifolium repens L., Wilting

Published in

Acta Universitatis Agriculturae Sueciae
2009, number: 2009:62
ISBN: 978-91-576-7409-8
Publisher: Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences

Authors' information

Arvidsson, Katarina (Arvidsson Segerkvist, Katarina)
Swedish University of Agricultural Sciences, Department of Agricultural Research for Northern Sweden

UKÄ Subject classification

Agricultural Science
Animal and Dairy Science

URI (permanent link to this page)

https://res.slu.se/id/publ/26278