-In the non breeding period, the effect of two superovulatory treatments (eCG/FSH in single dose or FSH alone in four decreasing doses) on the production of embryo quality following in vitro viability after vitrification procedures was investigated using forty-four adult Sarda breed ewes. In sheep treated with eCG/FSH, the mean number of corpora lutea was significantly (P < 0.05) higher (11.8 ± 4.0 vs. 8.05 ± 3.8), although the recovery rate was significantly (P < 0.01) lower (74.6 vs. 59.9) than with FSH alone. After vitrification (ethylene glycol and glycerol) was repeated three times, the rates of re-expansion at first and second warming were significantly (P < 0.01) higher in embryos derived from FSH alone than in those with both gonadotrophins (94.9 and 41.9 vs. 72.8 and 18.6) and after the last vitrification the hatched blastocyst rates were 22.5 and 7.6. After differential stain, blastocysts derived from FSH alone showed a mean number of cells significantly higher than blastocysts from eCG/FSH (184.2 vs. 157.7). It was concluded that superovulatory treatment with eCG/FSH may increase the ovarian responses compared with FSH alone, but these embryos showed a reduction in viability rates after repeated vitrification. superovulation / embryo quality / ovine / vitrification / viabilityRésumé -Les embryons ovins obtenus après un traitement de superovulation associant FSH et eCG ont une viabilité in vitro plus faible après vitrification que les embryons obtenus avec un traitement séquentiel de FSH. Pendant la saison non reproductive, on a évalué, chez 44 brebis adultes de race Sarde, l'effet de deux traitements de superovulation (le premier avec les eCG/FSH en une seule administration, le deuxième avec la FSH administrée en quatre doses décroissantes) sur la qualité des embryons produits et sur la viabilité in vitro après vitrification. Dans le groupe traité avec les eCG/FSH, le nombre moyen d'ovulations était plus élevé (11,8 ± 4,0 vs. 8,05 ± 3,8, P < 0,05) tandis que le taux de récupération était plus faible (74,6 vs. 59,9, P < 0,01) par rapport au groupe traité avec la FSH seule. Les embryons ont suivi 3 vitrifications successives (éthylène glycol et glycérol). Reprod. Nutr. Dev. 41 (2001) [239][240][241][242][243][244][245][246] 239

The aim of this work was to evaluate developmental competence and gene expression of prepubertal and adult ovine oocytes. GV prepubertal and adult oocytes were matured, fertilized and cultured in vitro until blastocyst stage;; the time (days) needed to reach this stage was recorded. Blastocysts developed on different days were cultured for hatching to evaluate their quality in relation to cleavage rate. Adult and prepubertal GV oocytes and blastocyst-stage embryos produced, respectively, at 6 and 7 days were compared for quantitative expression of poly(A) polymerase (polyA-P), glucose transporter I (Glut-I), desmocollin II (desmoII), plakofilin (plako) and heat shock protein 70.1 (HSP70) genes. Confirming previous results (Ledda et al., 1996 Zygote 4, 343–348), fertilized prepubertal ovine oocytes developed to blastocyst stage at lower rates than the adult ones (19.9 v. 51.3%, respectively, P&lt;0.001) and this stage was delayed 24h in prepubertal compared to adult embryos (P&lt;0.01), reflecting a lower quality (Fenwick et al., 2002 Hum. Reprod. 17, 407–412) of the former. In fact, 44.7, 25.0, 30.3 and 0% of adult blastocysts were obtained after 6, 7, 8 and 9 days, respectively, of postfertilization culture compared to 0, 48.4, 34.3 and 17.2% of prepubertal ones. Faster-developed blastocysts showed higher hatching rate in both prepubertal (54.8%, 7 days of culture) and adult (89.8%, 6 days). Hatching rate dropped to 18.2% when blastocysts were obtained at 8–9 days in prepubertal and to 54.5% and 32.5% at 7 and 8 days, respectively, in adult embryos. Analysis of gene expression showed that HSP70, plako and desmo genes were not expressed in GV oocytes, and Glut-I mRNA was lower in prepubertal GV oocytes than in the adult ones (P&lt;0.01). All genes were expressed in blastocysts;; we found that Glut-I was at lower levels (P&lt;0.01) in prepubertal-derived blastocysts whereas HSP70 was highly expressed (P&lt;0.05) in prepubertal blastocysts than in those derived from adult oocytes. In conclusion this work shows that prepubertal ovine oocytes have a lower developmental competence compared to the adult ones, correlated to an altered gene expression during the growth phase of the oocyte and early embryonic development. Supported by MIUR (cofin).