The objective of this study was to determine the effect of a linseed supplement on follicle growth, progesterone concentrations and milk and plasma fatty acids in dairy cows post partum. Sixteen Holstein cows were given a basal total mixed diet plus one of two supplements: control (C; extruded soybeans; n=8) or linseed (L; extruded linseeds; n=8). One month after calving oestrous cycles were synchronised (PRIDReg.). Follicle growth and milk progesterone concentrations were measured every 2 d over the induced oestrous cycle. Milk production characteristics were unaffected by treatment. The L cows lost significantly more BCS than the C cows (P< 0.01). Plasma insulin, glucose and urea were unaffected by the treatment. Plasma NEFA tended to be affected by the treatment (L > C, P=0.08). The proportions of 18:3n-3 in milk and plasma were increased by L compared to C (P<0.001 and P<0.01, respectively). There was an effect of dietary supplement on the numbers of small follicles (L < C, P<0.05). Milk progesterone was unaffected by treatment. In conclusion, the increased supply of 18:3n-3 to the cows had only a modest effect on follicle populations and corpus luteum activity was unchanged.