226 Effect of the presence or absence of corpus luteum in females with small antral follicles at the beginning of a progesterone-based oestrus synchronization protocol on superovulatory response and embryo yields in sheep

The high variability of responses to multiple ovulation and embryo transfer (MOET) programs is related to several factors, including the ovarian population present at the beginning of hormonal protocols. Thus, our objective was to evaluate the effect of the presence or absence of corpus luteum (CL) in females presenting small antral follicles (SF) at the beginning of a progesterone (P4)-based oestrus synchronization protocol on superovulatory response and embryo yields. The study was conducted during September and October in northeast Brazil (03°40′26″S and 40°14′20″W) using 15 adult Santa Inês ewes, in which the ovarian population present were SF (≤3.75mm, n=5) or SF plus CL (SF+CL, n=10) at the beginning of P4-based oestrus synchronization protocol. The females received a new or reused intravaginal device of progesterone (CIDR Eazi-breed, Zoetis) on Day 0, which remained for 9 days. On Day 7, the pFSH (133mg, Folltropin V, Vetoquinol) treatment was begun, with 6 decreasing doses (25, 25, 15, 15, 10, and 10%) injected IM at 12-h intervals. On Day 9, two equal doses of D-cloprostenol were injected at a 12-h interval (37.5μg, Prolise, Agener União). Flunixin meglumine (24.9 mg; Banamine, MSD Animal Health) was administered IM on Days 13 to 15. All ewes showed oestrus and were mated with fertile rams. On Day 16 non-surgical embryo recovery (NSER) was performed after cervical dilation using D-cloprostenol and oestradiol benzoate at 16h and ocytocin at 20min before. Transrectal B-mode ultrasound evaluations (Z5 Vet, Mindray) were performed on Day 0 and just before NSER to evaluate the ovarian population present. Data are showed in mean±s.d. and compared by t-test for independent samples (P<0.05). The number of CL present on NSER day (21.5±4.4 and 4.0±8.5) and the number of viable embryos (11.1±14.9 and 4.0±8.5) differed (P<0.05) between SF+CL ewes and SF ewes, respectively. However, the number of luteinizing unovulated follicles present on NSER day (4.5±2.5 and 12.4±7.8) and the number of recovered structures (i.e. embryos plus unfertilized eggs; 14.2±15.6 and 4.2±8.2) did not differ (P>0.05) between SF+CL ewes and SF ewes, respectively. In conclusion, the presence of a CL at the beginning of the oestrous synchronization protocol used for superovulation treatment affects responses to the MOET program. Financial support for this study was provided by Embrapa (02.13.06.026.00.02 and 02.13.06.026.00.04) and FAPEMIG (PPM 00201-17).