Strategies to improve cervical relaxation, ovarian response, and embryo yield in sheep undergoing non-surgical embryo recovery

Abstract

Multiple ovulation and embryo transfer (MOET) play a key role in accelerating sheep farming, but it is still limited by obstacles such as embryo recovery technique and variability in the superovulatory (SOV) response. This study evaluates alternatives to these limitations, aiming to increase in vivo embryo production in sheep. The first chapter reviews some relevant points of non-surgical embryo recovery (NSER): ovine cervical anatomy, physiological mechanisms of cervical relaxation, and current cervical relaxation protocols (PRC). The second and third chapters evaluate the efficiency of PRC using zero (0.0mg), half (0.5mg), or full dose (1.0mg) of estradiol benzoate (EB) in synchronized and/or superovulated ewes and its effects on NSER feasibility and luteal function. Sheep were randomly assigned to receive 37.5 µg of d-cloprostenol i.m. and 0.0 mg (0EB group; n=12); 0.5 mg (0.5EB group; n=12) or 1.0 mg EB (1.0EB group, n=12) 16 h before and 50 IU oxytocin i.v. 20 minutes before the NSER. In synchronized sheep, NSER was performed in 91.7% (33/36) with a longer transposition duration with Hegar dilator and longer catheter-mandrel (P<0.05) in 0.0EB. The treatments did not differ (P>0.05) in the duration of uterine flushing or the rate of structure recovery. In superovulated ewes, there was no treatment or category effect (P>0.05) concerning NSER success. There was a reduction (P<0.05) in ovarian biometry and progesterone (P4) concentration and an increase in estradiol (E2) concentration on D17. The fourth chapter assesses the effectiveness of hCG administration after ovulation. Ovarian function, P4 profile, and embryo yield were evaluated. Superovulated ewes received 300 IU of hCG i.m. (GhCG, n=24) or not (GControl, n=25) 96 h after P4 removal. NSER efficiency, SOV response, and luteal tissue area were similar between groups (P>0.05). The hCG increased (P<0.05) P4 levels and tended to prevent structural luteolysis (P=0.07) but had no effect (P>0.05) on functional luteolysis. The fifth chapter studies the effect of 250, 333, or 400 IU of a commercial pFSH (1FSH: 1LH) on follicular growth, SOV response, and embryo yield. Superovulated ewes with decreasing doses of 250 (G250), 333 (G333), or 400 IU (G400) of pFSH were submitted to NSER. Estrus response, estrus interval, CL and LUF counts and follicular growth did not differ (P>0.05) between groups. The treatments did not differ (P>0.05) in embryo yield, but G333 and G400 showed a tendency (P=0.06) to have a higher mean of recovered structures compared to G250. This study concludes that: 1) NSER can be successfully performed in different sheep breeds, regardless of category, using a cervical relaxation protocol without estradiol benzoate; 2) the use or not of EB affected the luteal function, interfering mainly in estradiol levels; 3) hCG treatment increased circulating P4 before NSER and may prevent early luteal regression; 4) protocols using 250, 333 and 400 IU of pFSH are efficient in promoting follicular growth and superovulatory responses, but 333 IU appears to be more efficient in increasing embryo yield. Keywords: Biotechnologies. Embryos. MOET. Transcervical.