title: Long-term effects of feeding monensin on milk fatty acid composition in lactating dairy cows.
abstract: The objective of this study was to determine the long-term effects of feeding monensin on milk fatty acid (FA) profile in lactating dairy cows. Twenty-four lactating Holstein dairy cows (1.46 +/- 0.17 parity; 620 +/- 5.9 kg of live weight; 92.5 +/- 2.62 d in milk) housed in a tie-stall facility were used in the study. The study was conducted as paired comparisons in a completely randomized block design with repeated measurements in a color-coded, double blind experiment. The cows were paired by parity and days in milk and allocated to 1 of 2 treatments: 1) the regular milking cow total mixed ration (TMR) with a forage-to-concentrate ratio of 60:40 (control TMR; placebo premix) vs. a medicated TMR [monensin TMR; regular TMR + 24 mg of Rumensin Premix per kg of dry matter (DM)] fed ad libitum. The animals were fed and milked twice daily (feeding at 0830 and 1300 h; milking at 0500 and 1500 h). Milk samples were collected before the introduction of treatments and monthly thereafter for 6 mo and analyzed for FA composition. Monensin reduced the percentage of the short-and medium-chain saturated FA 7:0, 9:0, 15:0, and 16:0 in milk fat by 26, 35, 19, and 6%, respectively, compared with the control group. Monensin increased the percentage of the long-chain saturated FA in milk fat by 9%, total monounsaturated FA by 5%, total n-6 polyunsaturated FA (PUFA) by 19%, total n-3 PUFA by 16%, total cis-18:1 by 7%, and total conjugated linoleic acid (CLA) by 43% compared with the control group. Monensin increased the percentage of docosahexaenoic acid (22:6n-3), docosapentaenoic acid (22:5n-3), and cis-9, trans-11 CLA in milk fat by 19, 13, and 43%, respectively, compared with the control. These results suggest that monensin was at least partly effective in inhibiting the biohydrogenation of unsaturated FA in the rumen and consequently increased the percentage of n-6 and n-3 PUFA and CLA in milk, thus enhancing the nutritional properties of milk with regard to human health.
authors.affiliation: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1. nodongo@uoguelph.ca
authors.forename: N E
authors.initials: NE
authors.lastname: Odongo
authors.forename: M M
authors.initials: MM
authors.lastname: Or-Rashid
authors.forename: R
authors.initials: R
authors.lastname: Bagg
authors.forename: G
authors.initials: G
authors.lastname: Vessie
authors.forename: P
authors.initials: P
authors.lastname: Dick
authors.forename: E
authors.initials: E
authors.lastname: Kebreab
authors.forename: J
authors.initials: J
authors.lastname: France
authors.forename: B W
authors.initials: BW
authors.lastname: McBride
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D005223:Fats / Q000032:analysis / Q000737:chemistry; D005227:Fatty Acids / Q000032:analysis*; D005260:Female; D007476:Ionophores / Q000008:administration & dosage / Q000494:pharmacology*; D007536:Isomerism; D007774:Lactation / Q000187:drug effects* / Q000502:physiology; D044243:Linoleic Acids, Conjugated / Q000032:analysis; D008892:Milk / Q000737:chemistry*; D008985:Monensin / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D005223:Fats; D005227:Fatty Acids; D007476:Ionophores; D044243:Linoleic Acids, Conjugated; D008985:Monensin