Pregnancy rate after ultrasound-guided follicle aspiration in nonlactating cows from different breeds

Thirty-six cows (21 Simmental, 5 Holstein-Frisian, 5 Brown Swiss and 5 Charolais) with high genetic superiority were punctured by ultrasound-guided follicle aspiration within the last 18 months for 503 times under equal conditions. Follicle aspiration was done twice per week. Most of the donor cows suffered from several disturbances of fertility. On average, 5 oocytes per session were collected. After in vitro maturation (IVM), fertilisation (IVF) and culture (IVC), 0.8 embryos per puncture session were transferred. After evaluation of the embryos by morphological criteria, these embryos were transferred to heifers that were oestrus synchronised (2.0 ml Estrumate i.m.) seven days after onset of oestrus. On day 21 after onset of oestrus the progesterone level in plasma was determined by radioimmunoassay. The pregnancy control was performed by ultrasound on day 35. After transfer of 397 embryos (to synchronised heifers), 125 pregnancies were established. Comparison of the different breeds and donor cows revealed significant differences in the number of oocytes recovered, embryos produced and pregnancies established. Transfer of embryos with insufficient morphological quality resulted in increased rates of embryonic loss between day 21 and day 35.