210 Potential predictors of ovarian responses and embryo yields in lactating Sarda ewes superovulated in a 4-day declining-dose PLUSET protocol

The aims of the present study were (1) to determine the efficiency of PLUSET on the ovulation rate and embryo yields in Sarda ewes, and (2) to evaluate an array of previously identified influencing factors (Bartlewski et al. 2016 Theriogenology 86, 130–143) for their usefulness as predictors of superovulatory responses in lactating Sarda ewes (May–June). These factors included the presence of corpus luteum (CL) at the beginning of the superovulatory treatment (D0), ewe age, milk productivity, day of lactation, and the numbers of antral follicles (total [TFN], small [2 mm; SFN], medium [3–4 mm; MFN], and large [≥5 mm; LFN] on D0 and throughout the period of PLUSET administration [D10–D13]). This study was conducted in a commercial farm located in Sardinia, Italy, and used 12 multiparous ewes (age, 4.3 ± 1.9 years; days of lactation, 174.8 ± 10.6; mean ± SD). Ewes were housed in a paddock and received the balanced Unifeed diet throughout the entire study period. Estrus was synchronized with a progesterone-releasing intravaginal device (CIDR®, 0.35 g, Zoetis) inserted for 7 days on D0 and then replaced with a new insert until D12. An i.m. injection of 125 µg of cloprostenol was given on D7. The superovulatory protocol consisted of eight consecutive injections of PLUSET (pFSH/pLH; 500 IU/10 mL) given at decreasing doses (2 × 1.8 mL, 2 × 1.5 mL, 2 × 0.7 mL, and 2 × 0.3 mL), at 0900 and 1900 hours, from D10 to D13. An i.m. injection of 400 IU of PMSG was given on D12. On D14, the ewes were naturally bred by two fertile Sarda rams. Transrectal ovarian ultrasonography utilizing the SonoScape S8 scanner equipped with a rigid, linear-array 10-MHz transducer was performed just before the insertion of the CIDR to confirm the presence/absence of CL and count all detectable ovarian antral follicles, and daily from D10 to D13 to enumerate ovarian follicles. Surgical embryo recovery was done 7 days after the end of PLUSET treatment. Superovulatory endpoints were compared between ewes with or without CL (n = 6/group) by Student t-test, and correlational analyzes used Pearson Product Moment tests (SigmaPlot®; Systat Software Inc.). The mean ovulation rate was 9.0 ± 2.6, and on average, 5.2 ± 2.7 embryos per ewe were collected. There were no differences (P > 0.05) in ovulatory responses or embryo yields between the ewes with or without CL on D0. We recorded the following significant correlations: MFN on D11 versus ovulation rate (OR; r = 0.61; P = 0.03), TFN on D12 versus OR (r = 0.62; P = 0.03), MFN on D12 versus OR (r = 0.71; P = 0.01); TFN on D12 versus embryo recovery rate (ERR; r = −0.71; P < 0.001), MFN on D12 versus ERR (r = −0.73; P = 0.007), MFN on D13 versus OR (r = 0.59; P = 0.04), and TFN on D13 versus ERR (r = −0.63; P = 0.03). In conclusion, total and medium-sized antral follicle numbers determined ultrasonographically during the period of gonadotropic ovarian stimulation are reliable predictors of ovulatory responses and embryo recovery rates in Sarda sheep superovulated in the PLUSET protocol.

Funding: Italian Ministry of Research and Education under the National Recovery and Resilience Plan, Ecosystem of Innovation for Next Generation Sardinia, ECS 00000038.