Successive in vivo embryo production in Santa Ines sheep

Context. In vivo embryo production, also called multiple ovulation and embryo transfer, can accelerate genetic gain, and thus improve animal production. However, there are issues limiting a wider use of this biotechnology in sheep livestock. Aims. This study aimed to determine (1) whether a previous response to superovulation (SOV) can be used as a criterion to select ewes for in vivo embryo production, (2) whether the intensity of the SOV response (number of corpora lutea, CL) can affect the embryo recovery rate, and (3) whether the number of CL quantified by colour Doppler ultrasonography can be used to calculate the recovery rate. Methods. Twenty-five Santa Ines ewes underwent SOV three times (SOV1, SOV2 and SOV3), with 200 mg FSH and natural mating. The number of CL after each SOV was determined by laparoscopy and by colour Doppler ultrasonography. Key results. The number of CL significantly decreased (P < 0.05) after SOV1 (7.5 +/- 4.8) to 3.0 +/- 5.0 at SOV 2 and 2.2 +/- 3.5 at SOV3. Strong correlations were observed between SOV2 and SOV3 in terms of numbers of CL (r = 0.86, r(2) = 0.74; P < 0.0001) and viable embryos (r = 0.79, r(2) = 0.63; P < 00001). However, no correlations were observed between SOV1 and SOV2 or between SOV1 and SOV3. Recovery rate did not differ with the intensity of the SOV response (<= 6, 7-10, > 10 CL) or between the methods used to quantify CL. Conclusions. Ewes did not show the same pattern of response when submitted to successive FSH-based SOV. The intensity of the SOV response did not affect the recovery rate, and the number of CL estimated by colour Doppler ultrasonography can be used to calculate the recovery rate. Implications. Selecting sheep embryo donors by a previous SOV response is not always feasible. The recovery rate is homogeneous and it is not affected by the intensity of the SOV response. A nonsurgical technique can be used to assess the recovery rate, improving animal welfare in MOET programs.