Concentration of plasma progesterone (ng/mL) by treatment. Control animals receiving the once-used controlled internal drug release (CIDR)
devices had plasma progesterone concentrations significantly higher
(P ¼ 0.01) than treatment animals receiving the twice-used CIDR devices
(3.37 Æ 0.53 vs. 1.40 Æ 0.47 ng/mL). Different letters represent P < 0.05.