Repeated superovulation of high-prolificacy Rasa Aragonesa ewes before culling as an inexpensive way to obtain high-quality embryos

The purpose of this study was to assess the ovulatory response and embryo production after repeated superovulation of selected high-prolificacy Rasa Aragonesa ewes at the end of their reproductive life. A total of 211 superovulatory treatments were performed during the breeding seasons of 3 consecutive years. Ewes were given the same gonadotrophin treatment up to three times at intervals of at least 50 days. They were synchronized with intravaginal progestagen sponges and treated with ovine follicle stimulating hormone (oFSH) equivalent to a total dose of 176 NIH-FSH-S1 units in eight decreasing doses administered at 12-h intervals from 72 h before sponge removal. Embryos were recovered by laparotomy 7 days after the onset of oestrus. There was no effect of year on the superovulatory response as measured by the percentages of ewes in oestrus (80%) or ovulating (67%). An average of four freezable embryos (compacted morulae and blastocysts) were recovered at each treatment from the 141 ovulating ewes, with no significant differences amongst years, although the process seemed to be less efficient after the third treatment than after the first or second ones (2.4 vs. 4.1 (P < 0.10) or 4.5 (P < 0.05) freezable embryos, respectively). This was primarily attributable to a lower ovulation rate (three fewer corpora lutea; P < 0.10). Results indicate that the methodology used in the present study could be an efficient and inexpensive way to obtain high-quality embryos from selected high-prolificacy animals before culling. (C) 2000 Elsevier Science B.V. All rights reserved.