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Addition of fish oil to diets for dairy cows. II. Effects on milk fat and gene expression of mammary lipogenic enzymes

Published online by Cambridge University Press:  22 November 2002

CHARAF E. AHNADI
Affiliation:
Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, P.O. Box 90, Lennoxville, QC, Canada J1M 1Z3 Present address: Département de biochimie clinique, Centre universitaire de santé de l’Estrie, 3001, 12ème Avenue Nord, Sherbrooke, QC, Canada J1H 5N4.
NAOMI BESWICK
Affiliation:
University of Alberta, Department of Agricultural, Food and Nutritional Science, Edmonton, AB, Canada T6G 2P5
LOUIS DELBECCHI
Affiliation:
Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, P.O. Box 90, Lennoxville, QC, Canada J1M 1Z3
JOHN J. KENNELLY
Affiliation:
University of Alberta, Department of Agricultural, Food and Nutritional Science, Edmonton, AB, Canada T6G 2P5
PIERRE LACASSE
Affiliation:
Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, P.O. Box 90, Lennoxville, QC, Canada J1M 1Z3

Abstract

Sixteen Holstein cows in mid-lactation were used to determine whether alterations of mammary fatty acid metabolism are responsible for the milk fat depression associated with consumption of fish oil. Cows were given a total mixed ration with no added fish oil (control), unprotected fish oil (3.7% of dry matter), or glutaraldehyde-protected microcapsules of fish oil (1.5% or 3.0% of dry matter) for 4 weeks. Milk samples were taken once a week and a mammary biopsy was taken from a rear quarter at the end of the treatment period. Milk fat content was lower in cows given unprotected fish oil (26.0 g/kg), 1.5% protected fish oil (24.6 g/kg) and 3% protected fish oil (20.4 g/kg) than in cows fed the control diet (36.0 g/kg). This was mainly due to a decrease in the synthesis of short-chain fatty acids. Consumption of protected fish oil decreased the abundance of lipogenic enzymes mRNA in the mammary gland. Acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase mRNAs for cows given 3% protected fish oil averaged only 30%, 25% and 25% of control values, respectively. Dietary addition of unprotected fish oil slightly decreased mRNA abundance of these enzymes but markedly reduced the amount of lipoprotein lipase mRNA. Milk fat content was significantly correlated with gene expression of acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase but not lipoprotein lipase. These results suggest that fish oil reduces milk fat percentage by inhibiting gene expression of mammary lipogenic enzymes.

Type
Original article
Copyright
Proprietors of Journal of Dairy Research 2002

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