Eight Holsteincows with body weight 570 ± 43 kg and 60 ± 20 lactation days weredistributed in a double Latin square design with four 21-day periods to determinethe effects of feeding ground or whole flaxseed with or without monensin supplementation(0.02% on a dry matter basis) on fatty acid profile of butter stored for 15and 45 days. Ground flaxseed supply, in comparison to whole flaxseed, reducedrelative percentages of 16:0, cis7-16:1, 17:0, and cis10-17:1 but it increasedthose of cis9,trans11-18:2, cis3-18:3, and omega 3 fatty acids in butter fat,reducing relative percentage of medium-chain fatty acids and increasing thecontent of polyunsaturated fatty acids. Supplementation with monensin increasedrelative percentages of cis9,trans11-18:2 and tended to increase relative percentageof 17:0 and decrease that of saturated fatty acids in butter. Butter from cowsfed diet with monensin presented lower relative percentages of cis 6-20:4. Relativepercentages of cis 9-16:1, cis10-17:1, 18:0, trans11-18:1, cis9-18:1, cis3-18:3,cis6-20:4 in butter stored for 15 days were higher than those stored for 45days and the relative percentages of cis3-20:5 tended to decrease with the increaseof storage period. As a result, relative percentages of saturated fatty acidsand medium-chain fatty acids increased with storage time, while those of monounsaturatedand long-chain fatty acids decreased. Butter enriched with polyunsaturated fattyacids may have a shorter shelf life due to the negative effect of storage onfatty acid profile which may cause oxidation and rancidity.
