144 PREGNANCY RATES FOLLOWING THE TRANSFER OF IN VITRO FERTILIZED EMBRYOS TO RECIPIENTS ON DAY 6, 7, OR 8 AFTER OESTRUS

Abstract

The aim of this experiment was to investigate the effect of day of synchrony on the pregnancy rate of recipients following the transfer of Day 7 IVF embryos. In addition, the effect of IVF embryo grade and corpus luteum (CL) grade of recipients was determined. A total of 317 cumulus-oocyte complexes collected from 24 dry Brahman cows by TVR were matured, fertilized, and cultured under standard in vitro production procedures (Fry et al. 2003 Theriogenology 59, 446). A total of 89 (44 Grade 1, 43 Grade 2, and 2 Grade 3, IETS classification) in vitro-produced embryos were transferred to parous 4- to 9-year-old dry Brahman cross recipient cattle 7 days after IVF. Two groups of recipient cows were synchronised one day apart with an 8-day CIDR/pg protocol so that oestrous would be concentrated over 3 days with the middle day aligning with the day of IVF (Day 0). Donors that produced a large number of IVF embryos had these divided and transferred into recipients either on Day –1 or Day +1 of synchrony, and those producing less than 4 IVF embryos were transferred into recipients on Day 0. At embryo transfer the ovaries of the recipient were palpated and then scanned by rectal ultrasound and the grade of CL noted (Grade 1 = large distinct CL by palpation, Grade 2 = small distinct CL by palpation, Grade 3 = CL not distinguishable by palpation). Pregnancy was diagnosed by ultrasound scanning on Day 92. Although recipient numbers were low, differences in pregnancy rate between groups were analysed by Chi-squared. Data from the 2 Grade 3 embryos transferred were not included in the analysis (0/2 pregnant). Similar (P > 0.05) pregnancy rates were found when Day 7 IVF embryos were transferred to either Day 6 (17/32 = 53%), Day 7 (9/24 = 38%), or Day 8 (14/31 = 45%) recipients. Furthermore, neither the grade of the embryo (Grade 1: 20/44 = 45%, Grade 2: 20/43 = 47%) nor the grade of recipient CL (Grade 1: 17/45 = 38%, Grade 2: 17/29 = 59%, Grade 3: 6/13 = 46%) effected pregnancy rate (P > 0.05). This experiment demonstrates the flexibility of the IVF embryo to achieve an acceptable pregnancy rate over a range of recipient stages thereby allowing a high usage rate of good-quality recipients in an IVF embryo transfer program.