Effect of silage type and concentrate level on conjugated linoleic acids, trans-C18:1 isomers and fat content in milk from dairy cowsTina S. Nielsena, Ellen M. Straarupb, Mogens Vestergaarda and Kris Sejrsena
a Danish Institute of Agricultural Sciences, Research Centre Foulum, Department of Animal Health, Welfare and Nutrition, PO Box 50, 8830 Tjele, Denmark
b BioCentrum, Technical University of Denmark, 2800 Lyngby, Denmark
(Received 11 January 2006; accepted 22 August 2006; published online 15 December 2006)
Abstract - The objective of the study was to examine how the fatty acid composition of milk especially concentrations of conjugated linoleic acids (CLA) and trans-C18:1 isomers and milk fat percentage were affected by silage type and concentrate level. Forty dairy cows were blocked and randomly assigned to one of four diets in a factorial arrangement of treatments and a six week experimental period. Treatments were total mixed rations with maize (M) or grass (G) silage differing in polyunsaturated fatty acid (PUFA) profile and starch content, combined with a high (H) or a low (L) level of concentrate (with or without grain). Treatments had no significant effect on milk, protein and lactose yield, but energy corrected milk yield, milk fat percentage and fat yield was lower and protein percentage higher for maize compared with grass silage diets. Overall, maize silage diets resulted in higher concentrations of CLA isomers compared with grass silage diets, but there was a significant interaction between silage type and concentrate level for concentrations of cis9,trans11-CLA; trans10,cis12-CLA; trans11-C18:1 and trans10-C18:1. A high level of concentrate increased trans10,,cis12-CLA and trans10-C18:1 and reduced cis9,trans11-CLA and trans11-C18:1 when maize but not grass silage was provided. The results suggest that high levels of concentrate (grain) do not significantly alter the pattern of PUFA biohydrogenation in the rumen, the concentration of CLA and trans-C18:1 isomers in milk or cause milk fat depression unless combined with forage naturally high in starch and C18:2n-6 such as maize silage.
Key words: CLA / trans-C18:1 isomers / milk fat / silage type / concentrate level
Corresponding author: TinaS.Nielsen@agrsci.dk
© INRA, EDP Sciences 2006