ABSTRACT
During spring, summer and winter seasons, Sistani donor cows, with normal reproductive status, were superovulated and embryos were recovered non-surgically on day 7. Grade A blastocyst embryos were either transferred fresh [spring] or frozen [summer and winter]. Recovered embryos during summer and winter were exposed to glycerol and frozen using conventional method. During spring season, recipient females [n = 70] were synchronized using two consecutive injections of prostaglandin F[2alpha] analogue, 14 days apart. On day 7 after the ensuing cycle, the females were assigned into three groups to receive single embryo, either fresh [n = 14; control; recovered embryos in spring] or frozen blastocyst recovered and frozen in summer [n = 27] or winter [n = 29]. Pregnancies were diagnosed by ultrasound examination, 30 days after non-surgical embryo transfer. Pregnancy rates following transfer of fresh embryos [64.3%] were higher than those that received frozen-thawed embryos [17.86%; P<0.05]. There was not any significant difference between pregnancy rates of recipients receiving embryos frozen in summer [18,5%] or winter [17.2%; P>0.05]