Effects of seasonal variation and winter supplementation of ground whole flaxseed on milk fatty acid composition of dairy cows in organic farms in the northeastern United States

Fourteen organic dairy farms in the northeastern United States were used to evaluate (1) seasonal variation in bioactive milk fatty acid (FA) profile from 2012 to 2015 and (2) supplementation of ground whole flaxseed (GFLX) to maintain elevated concentrations of bioactive milk FA during the nongrazing season. During regular farm visits, milk, feed, and pasture samples were collected, and diet composition, milk yield, and milk composition were recorded. During winters of 2013 to 2014 and 2014 to 2015, 9 farms supplemented GFLX at 6% of diet DM to half of each herd (n = 238 cows per treatment). Milk samples were collected and pooled by treatment (GFLX or control). Data were analyzed using the MIXED procedure of SAS. A significant month × year interaction (P < 0.05) for n-3 FA showed an increase beginning in April of 2014 through the end of the study. The proportion of conjugated linoleic acid showed a seasonal pattern with greatest (P < 0.05) concentrations (1.32% of total milk FA) during the grazing season. Winter GFLX supplementation did not affect (P > 0.15) milk yield or concentrations of milk fat or protein; however, BCS tended (P = 0.08) to be greater for GFLX cows. Compared with the control diet, GFLX decreased (P < 0.05) total milk SFA by 3.1 percentage units and increased (P < 0.05) n-3 by 62% and total conjugated linoleic acid proportion by 9%. Although GFLX supplementation increased milk n-3, lesser effects on SFA and total conjugated linoleic acid proportions indicated that a greater level of winter supplementation is required to improve overall milk FA profile during the nongrazing season.