To evaluate the effects of physically processed flaxseed [ground flaxseed (GFS) and whole flaxseed (WFS)] as a replacement for extruded soybeans on feed intake, milk production, milk composition, milk fatty acid (FA) composition and blood biochemical parameters, nine primiparus Holstein dairy lactating cows averaging 495 ± 34.5 kg of body weight (BW) and 70 ± 5 days in milk (DIM) were assigned in a 3 × 3 change over Latin square design with three periods. Intake of dry matter was similar among the animals fed the treatments, also milk yield and milk composition were not influenced by the diets. Processing of flaxseed significantly (P<0.05) affected plasma glucose and urea concentrations. Feeding ground compared with whole flaxseed and extruded soybeans, caused a significant (P<0.05) increase in the concentration of total long-chain fatty acids in milk, also α-linolenic acid (18:3) content nearly doubled with GFS compared with those of the other treatments (0.75 vs. 0.36 and 0.46 g/kg milk production for GFS, ESB or WFS, respectively). Linoleic acid (18:2), content of milk was also significantly (P<0.05) increased by inclusion of the ground flaxseed compared with the other treatments. In general, feeding ground flaxseed had a significant (P<0.05) effect on monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) concentrations compared with those of the cows fed extruded soybeans or whole flaxseed.

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