The aim of the investigation was to determine the influence of flaxseed of two varieties, differing in their fat composition, on blood indices of cows in the transition period and on their reproductive parameters. Fifty-six multiparous Polish Holstein-Friesian cows were allocated into 3 groups: one control and two experimental (H-ALA and L-ALA). Cows of all groups were fed the same basal diet given in a mix form, and the diets of the experimental groups were enriched with an additive of flaxseed (mixed with concentrate), of either a traditional variety (Szafir, rich in α-linolenic acid, H-ALA group) or a modified variety (Amon, poor in α-linolenic acid but rich in linoleic acid, L-ALA group) given in the amounts of 3% and 6% of diet dry matter (DM) during 6 wks prior to the calving and during 17 wks of lactation, respectively. Blood plasma samples, collected 4 times, were analyzed for the contents of glucose (GLU), urea, total protein (TP), non-esterified fatty acids (NEFA), β-hydroxybutyric acid (BHBA), total cholesterol (CHOL), triacylglycerols (TG), HDL cholesterol fraction, and plasma fatty acid (FA) profile. Reproductive parameters of cows were determined as well. Flaxseed of both varieties did not have any significant influence on the GLU or TG contents in blood plasma. Both the BHBA and NEFA contents in all treatments were much below the undesirable levels and flaxseed supplement decreased additionally (p ≤ 0.05) the NEFA concentration in plasma in the 2nd wk after calving, with the stronger impact of the traditional flax (decrease by 37% compared with the control cows), which may point to lower adipose tissue mobilization in these animals. The flaxseed additive increased (p ≤ 0.05) the plasma CHOL content, especially in the case of the modified flax variety. The traditional variety of flax increased (p ≤ 0.05) the blood plasma level of α-linolenic acid (ALA), which is recognized as a component inhibiting PGF2α secretion, thus decreasing embryonic mortality in the first weeks after insemination. However, we did not note any significant improvement in the reproductive indices of cows fed seeds of this flax variety. The results suggest that diets enriched with flaxseed of the traditional variety (rich in ALA) in the amount of 6% of diet DM in early lactation increase the blood plasma level of this FA without causing a considerable improvement in cows’ reproductive parameters.
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