“…Indeed, electrical activation of the in vitro matured bovine oocytes was found to be oocyteage-dependent and poor activation results were obtained with oocytes matured in vitro less than 30 h (Ware et al, 1989;Yang et al, 1991 Thus, at one time, most nuclear transfer programs involved using aged oocytes as recipients (Willadsen et al, 1991;Westhusin et al, 1992;Yang et al, 1993a). More recently, improvements on activation procedures have resulted in suc-cessful activation and led to the use of young oocytes for nuclear transfer (First et al, 1992;Barnes et al, 1993;Yang et al, 1993b;Aoyagi ef al, 1994;Heyman et al, 1994;Stice et al, 1994).…”