320 INFLUENCE OF PROGESTERONE AND MOMENT OF ESTRADIOL BENZOATE INJECTION ON MULTIPLE-OVULATION EMBRYO TRANSFER RESULTS

Abstract

Current superovulatory treatment combines progesterone as well as oestradiol injection at the moment of CIDR insertion to improve synchronization of follicular wave emergence [reviewed by Bo et al. 2002 Theriogenology 57, 53–172; and Mapletoft et al. 2003 J. Anim. Sci. 81 (E. Suppl.), E28–E36] The aim of the present work was to study if delaying oestradiol benzoate (EB) injection 24 or 48 h from CIDR insertion would have the same outcome on embryo production after superovulatory treatment as additional progesterone administered at CIDR insertion. One hundred and eleven superovulatory treatments conducted during the same period (5 consecutive collection days) at random stages of the oestrus cycle at the same location were retrospectively evaluated. Holstein cycling heifers of 18 months of age (body condition score 3.2 ± 0.28, 1–5 range; weighing 357 ± 28 kg) were divided according to the following treatments: control group (n = 24): Day 0: CIDR insertion (Pfizer Animal Health, New York, NY, USA), 50 mg of progesterone, and 2 mg of oestradiol benzoate (Benzadiol, Universal Laboratory, Montevideo, Uruguay); Group BE24 (n = 47): Day –1: CIDR insertion and Day 0: 2 mg of oestradiol benzoate; Group BE48 (n = 40): Day –2: CIDR insertion and Day 0: 2 mg of oestradiol benzoate. All heifers were superstimulated on Day 3.5 (Day 0 = EB injection) with 290 NIH units of FSH (Folltropin, BionicheAnimal Health, Belleville, ON, Canada) in twice-daily decreasing doses over 4.5 days. On Day 6, all cows received 2 doses (a.m. and p.m.) of a prostaglandin F2α analogue (800 µg, Delprostenate, Glandinex, Universal Laboratory), and CIDR were removed on the morning of Day 7. Cows were injected with 10 µg of GnRH (Receptal, Intervet, Boxmeer, the Netherlands) on Day 8 a.m. and were inseminated 12 and 24 h later with semen of 3 bulls of proven fertility. On Day 15, ova/embryos were collected nonsurgically and evaluated in accordance with IETS guidelines. Data were analysed with a negative binomial regression model (Table 1). Administration of EB 24 or 48 h after CIDR insertion produced similar numbers of transferable and freezable embryos as well as total ova/embryos compared with addition of progesterone and EB at the moment of CIDR insertion. According to these results, EB could be administrated without progesterone injection either 24 or 48 h after CIDR insertion without compromising embryo production. Table 1.Embryo production of heifers superstimulated after additional progesterone (P4) and different times (24 or 48 h after CIDR insertion) of oestradiol benzoate administration (results are mean ± SE)