140 A comparison of in vitro embryo production between heifers and lactating Holstein donors without superstimulation

Abstract

Bovine oocyte donor age seems to have an important role on in vitro embryo production. Therefore, the aim of this study was to compare cumulus-oocyte complex (COC) recovery, cleavage, and blastocyst rates between heifers and lactating Holstein donors. A total of 89 animals (heifers: n = 60, 11 to 17 months of age; lactating cows: n = 29, 60 to 180 days in milk) were used in this experiment. Ovum pickup (Day −1) was performed on a random day of the oestrous cycle without superstimulation by a single technician. Conventional or sexed semen were used for IVF (Day 0). Cleavage and blastocyst rates were evaluated on Days 3 and 7, respectively. Cleavage was determined when structures had 4 or more cells and blastocyst rate included grades I and II blastocysts. Continuous data were analysed by t-test, and binomial data were analysed by Fischer’s exact test. A total of 1,289 COC were recovered from lactating cows (n = 509) and heifers (n = 777). Total and viable COC per donor were higher (P < 0.05) in lactating cows (total = 17.55 ± 13.08; viable = 11.24 ± 8.9) than heifers (total = 12.95 ± 5.39; viable = 7.88 ± 4.08). The percentage of viable COC was similar (P > 0.05) in lactating cows (64.04%; 326/509) and heifers (60.87%; 473/777). Cleavage rate was higher (P < 0.0001) in lactating cows (58.74%; 299/509) than in heifers (45.05%; 350/427). Cleavage rate was similar (P > 0.05) with conventional and sexed semen in heifers (conventional = 37.68%; 52/138; sexed = 46.63%; 298/639) and cows (conventional = 55.05%; 49/89; sexed = 59.52%; 250/470). Blastocyst rate was higher (P < 0.0001) in lactating cows (19.84%; 101/509) than in heifers (8.49%; 66/777). Conventional semen had a higher (P < 0.0001) blastocyst rate (18.11%; 24/138) than sexed semen (6.57%; 42/639) in heifers. However, there was no difference (P > 0.05) in blastocyst rate between conventional (24.71%; 22/89) and sexed semen (18.8%; 79/420) in lactating cows. Blastocyst/cleaved structures ratio was higher (P < 0.05) in heifers using conventional (46.15%; 24/52) compared with sexed (14.06%; 42/298) semen. However, in lactating cows there was a tendency (P < 0.1) for higher blastocyst/cleaved structures ratio using conventional (44.89%; 22/49) compared with sexed semen (31.6%; 79/250). In conclusion, a higher number of total and viable COC were aspirated from Holstein lactating cows than heifers. Furthermore, cleavage and blastocyst rates were higher in lactating cows than in heifers. Conventional semen gave more embryos than did sexed semen in heifers but not in cows. Overall, oocytes from Holstein lactating donors are more suitable for in vitro embryo production than are those from heifer donors.