Effect of daytime grazing of fresh grass without supplemental feed on serum and milk a-tocopherol concentrations of holstein dairy cows

The effect of switching 5 Holstein dairy cows from concentrate-fed to roughage-fed conditions without supplemental feed for seven weeks on serum parameters and milk chemical composition in morning and afternoon milk samples was investigated. BW was not affected and blood hematocrit and total protein, glucose and triglyceride concentrations varied within normal values throughout the experiment. During day grazing period, serum non-esterified fatty acid (NEFA), milk somatic cell counts (SCC), total solids, lipids and milk and serum a-tocopherol values increased, whereas, those of milk yield, milk protein, lactose and solids-non-fat decreased. For diurnal changes, NEFA concentrations were lower, whereas, SCC, milk lipid and milk a-tocopherol concentrations were higher in the afternoon. Changes in milk chemical composition, when cows were switched from concentrate-fed to roughage-fed conditions including daytime grazing, were related to the chemical composition of the feeds consumed.