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

A total of 32 Holstein cows were allotted at calving to eight groups of four cows blocked to determine the effects of feeding increased levels of whole flaxseed (WF) in the diet on dry matter (DM) intake (DMI), milk production and composition, milk fatty acid (FA) profile, concentration of some blood metabolites and energy balance. Cows within each block were assigned to one of four iso-net energy for lactation total mixed rations: no whole flaxseed (0WF), and diets with preplanned inclusions of 50 (50WF), 100 (100WF) or 150 (150WF) g/kg DM WF. Diets were fed for ad libitum intake from calving to week 24 of lactation. There was a trend for an interaction between treatment and week for DMI, milk yield, and logsomatic cell count (P=0.08, 0.07, and 0.09, respectively). Values of DMI averaged for the 24 week experiment, yields of fat, protein and total solids and proportions of short- and medium-chain FA in milk fat decreased linearly with higher proportions of WF in the diet. Milk yield was similar among diets. Proportions of 18:0, cis9-18:1, trans9-18:1, cis9,trans11-18:2, cis9,12,15-18:3 19:0 and 20:0 in milk fat increased linearly and those of cis9,12-18:2, trans9,12-18:2 and 20:4 decreased linearly with higher concentrations of WF in the diet. Although milk FA profile was enhanced, feeding more than preplanned inclusions of 50 g/kg DM WF had negative effects on yield of milk components.