Milk production and composition, milk fatty acid profile, and blood composition of dairy cows fed whole or ground flaxseed in the first half of lactation

A total of 27 multiparous Holstein cows averaging 634 kg body weight (BW) were allotted at calving to six groups of four cows and one group of three cows blocked for similar calving dates to determine effects of feeding whole or ground flaxseed on dry matter (DM) intake, milk production, milk composition, milk fatty acid profile and concentration of some blood metabolites. Cows within each block were assigned to one of four iso-net energy for lactation total mixed rations containing either 21 g/kg DM calcium salts of palm oil (control diet), 72 g/kg DM whole flaxseed, 72 g/kg DM ground flaxseed or 36 g/kg DM whole flaxseed and 36 g/kg DM ground flaxseed. Diets were fed for ad libitum intake from calving to week 28 of lactation. Flaxseed grinding and supplementation had no effect on BW and milk production, but intake of DM was lower for cows fed 72 g/kg DM ground flaxseed. The main difference in milk fatty acid profile determined on week 8 of lactation due to flax grinding was for linolenic acid proportion, which was higher in milk fat of cows fed ground (36 or 72 g/kg DM) flaxseed compared to cows fed 72 g/kg DM whole flaxseed. Flaxseed supplementation enhanced the linolenic acid proportion in milk fat compared to the control diet. Cows fed the control diet had higher proportions of 16:0 and cis7-16:1, and lower proportions of 18:0 and cis9-18:1, in milk fat than those fed flaxseed. Cows fed ground flaxseed tended (P=0.07) to have higher plasma concentrations of β-hydroxybutyrate (BHBA) than those fed the other diets. Compared to diets containing 21 g/kg DM calcium salts of palm oil, 72 g/kg DM whole flaxseed or a mixture of 36 g/kg DM ground and 36 g/kg DM whole flaxseed, feeding 72 g/kg DM ground flaxseed may contribute to increased lipolysis of early lactation cows, as indicated by lower DM intake and higher BHBA concentrations in blood.