COPPER STATUS AND REQUIREMENT DURING THE DRY PERIOD AND EARLY LACTATION IN MULTIPAROUS HOLSTEIN COWS

Eighteen multiparous Holstein cows were assigned randomly to three tre atments at the beginning of the dry period (8 wk before expected partu rition). Treatments were 1) the basal diet containing 5.5 ppm of Cu (c ontrol), 2) the basal diet supplemented with 10 ppm of Cu, and 3) the basal diet supplemented with 20 ppm of Cu. The objectives were to meas ure the changes of Cu and other trace mineral element concentrations i n blood and liver from the onset of the dry period (approximately 8 wk prepartum) to 8 wk postpartum and to assess the requirement of Cu dur ing this time. Liver Cu concentration in the control group declined co ntinuously during the 8-wk dry period, and the nadir occurred at partu rition. This decline was prevented by dietary Cu supplementation of 10 or 20 ppm. Liver Cu concentration in the control group started to inc rease slowly after the dramatic decline. Liver Zn concentration change d cubically as a function of week during the treatment period. Plasma Cu and Zn exhibited a quadratic pattern as a function of week. The pla sma Cu concentration was lowest 5 wk prior to parturition.