Pregnancy rates of frozen embryos recovered during winter and summer in Sistani cows

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 F2α 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).