title: Dietary fish oil supplements depress milk fat yield and alter milk fatty acid composition in lactating cows fed grass silage-based diets.
abstract: The potential of dietary fish oil (FO) supplements to increase milk 20:5n-3 and 22:6n-3 concentrations and the associated effects on milk fatty acid (FA) composition, intake, and milk production were examined. Four multiparous lactating cows offered a grass silage-based diet (forage:concentrate ratio 58:42, on a dry matter basis) supplemented with 0, 75, 150, or 300g of FO/d (FO0, FO75, FO150, and FO300, respectively) were used in a 4×4 Latin square with 28-d experimental periods. Milk FA composition was analyzed by complementary silver-ion thin-layer chromatography, gas chromatography-mass spectrometry, and silver-ion HPLC. Supplements of FO decreased linearly dry matter intake, yields of energy-corrected milk, milk fat and protein, and milk fat content. Compared with FO0, milk fat content and yield were decreased by 30.1 and 40.6%, respectively, on the FO300 treatment. Supplements of FO linearly increased milk 20:5n-3 and 22:6n-3 concentrations from 0.07 to 0.18 and 0.03 to 0.10g/100g of FA, respectively. Enrichment of 20:5n-3 and 22:6n-3 was accompanied by decreases in 4- to 18-carbon saturated FA and increases in total conjugated linoleic acid (CLA), trans FA, and polyunsaturated FA concentrations. Fish oil elevated milk fat cis-9,trans-11 CLA content in a quadratic manner, reaching a maximum on FO150 (from 0.61 to 2.15g/100g of FA), whereas further amounts of FO increased trans-10 18:1 with no change in trans-11 18:1 concentration. Supplements of FO also resulted in a dose-dependent appearance of 37 unique 20- and 22-carbon intermediates in milk fat. Concentrations of 16-, 18-, 20-, and 22-carbon trans FA were all increased by FO, with enrichment of trans 18:1 and trans 18:2 being quantitatively the most important. Decreases in milk fat yield to FO were not related to changes in milk trans-10,cis-12 CLA concentration or estimated milk fat melting point. Partial least square regression analysis indicated that FO-induced milk fat depression was associated with changes in the concentrations of multiple FA in milk. Even though a direct cause and effect could not be established, a decrease in 18:0 supply in combination with increased mammary uptake of cis-11 18:1, trans-10 18:1, and trans 20- and 22-carbon FA may contribute. In conclusion, dietary FO supplements enrich 20:5n-3 and 22:6n-3 in milk, but also elevate mono- and polyenoic trans FA concentrations, and in high amounts alter the distribution of individual trans FA isomers.
authors.affiliation: Natural Resources Institute Finland, Nutritional Physiology, Green Technology, FI-31600 Jokioinen, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Kairenius
authors.affiliation: Natural Resources Institute Finland, Nutritional Physiology, Green Technology, FI-31600 Jokioinen, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Ärölä
authors.affiliation: Natural Resources Institute Finland, Nutritional Physiology, Green Technology, FI-31600 Jokioinen, Finland.
authors.forename: H
authors.initials: H
authors.lastname: Leskinen
authors.affiliation: Natural Resources Institute Finland, Nutritional Physiology, Green Technology, FI-31600 Jokioinen, Finland.
authors.forename: V
authors.initials: V
authors.lastname: Toivonen
authors.affiliation: Natural Resources Institute Finland, Nutritional Physiology, Green Technology, FI-31600 Jokioinen, Finland.
authors.forename: S
authors.initials: S
authors.lastname: Ahvenjärvi
authors.affiliation: Department of Agricultural Sciences, University of Helsinki, PO Box 28, FI-00014 Helsinki, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Vanhatalo
authors.affiliation: Natural Resources Institute Finland, Nutritional Physiology, Green Technology, FI-31600 Jokioinen, Finland; Department of Agriculture for Northern Sweden, Swedish University of Agricultural Sciences, S-90183 Umeå, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Huhtanen
authors.affiliation: Natural Resources Institute Finland, Statistical Methods, Management and Production of Renewable Resources, FI-31600 Jokioinen, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Hurme
authors.affiliation: Department of Agricultural Sciences, University of Helsinki, PO Box 28, FI-00014 Helsinki, Finland.
authors.forename: J M
authors.initials: JM
authors.lastname: Griinari
authors.affiliation: Natural Resources Institute Finland, Nutritional Physiology, Green Technology, FI-31600 Jokioinen, Finland; Institute of Biological, Environmental and Rural Sciences, Animal and Microbial Sciences, Aberystwyth University, Aberystwyth, SY23 3EB, United Kingdom. Electronic address: kes14@aber.ac.uk.
authors.forename: K J
authors.initials: KJ
authors.lastname: Shingfield
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D005223:Fats / Q000032:analysis; D005227:Fatty Acids / Q000032:analysis* / Q000378:metabolism; D005260:Female; D005285:Fermentation; D005395:Fish Oils / Q000008:administration & dosage*; D007774:Lactation; D044243:Linoleic Acids, Conjugated / Q000032:analysis; D008892:Milk / Q000737:chemistry*; D009851:Omasum / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism; D012417:Rumen / Q000378:metabolism / Q000382:microbiology; D012820:Silage
chemical_list: D005223:Fats; D005227:Fatty Acids; D005395:Fish Oils; D044243:Linoleic Acids, Conjugated
keywords: conjugated linoleic acid; fish oil; milk fat; trans fatty acid