104 SOFaaci-HEPES or holding media can be used for embryo loading without changes in pregnancies per embryo transfer nor pregnancy loss in an invitro-produced embryo transfer program
Authors: Pereira D. , Moreno D. , Sala R. , Carrenho-Sala L. , Fosado M. , Moreno J. , Garcia-Guerra A. 
Published: December 2019

Time elapsed between removal from culture and embryo transfer (ET) can have a profound effect on the success of an invitro-produced (IVP) ET program. The embryo culture medium provides the necessary nutrients for embryo development and the use of media with a different nutrient composition to load embryos into straws could negatively affect embryo viability. The objective of the present study was to evaluate the effect of type of media used for embryo loading on pregnancy establishment and maintenance. Holstein heifers (n=800) were synchronized using a modified 5-day CO-Synch + controlled internal drug release (CIDR) as follows: Day −8: CIDR inserted, Day −3: CIDR removed, prostaglandin F2α treatment (500μg cloprostenol sodium), Day 0: gonadotrophin-releasing hormone (GnRH; 100μg of gonadorelin acetate). Five days after GnRH, heifers were evaluated by ultrasonography to determine presence of a corpus luteum (CL). Embryos were removed from culture on Day 7 (Day 0=fertilization), placed into tubes containing SOFaaci, and transported in an incubator (LabMix, WTA) to the transfer facility within 1.5h. Upon arrival embryos were removed from transport tubes and randomly assigned to be loaded into 0.25-mL straws containing either holding media (Vigro Holding Plus) or SOFaaci-HEPES. After loading into straws, embryos were placed in an ET gun and AI gun warmers set at 35°C until transfer by 1 of 5 technicians. Heifers with a CL were randomised for transfer of a fresh IVP embryo loaded into a straw containing either holding media or SOFaaci-Hepes on Day 7±1. Interval from embryo loading to transfer ranged from 1 to 3h. Pregnancy was determined by ultrasonography on Days 32 and 60. Data were analysed by logistic regression and included the fixed effects of loading media, embryo stage, embryo quality, interval between GnRH and ET, and biologically relevant interactions. Pregnancies per ET (P/ET) on Day 32 were not different between the groups in which embryos were loaded using holding media and those which used SOFaaci-Hepes, nor there were interactions between loading medium and embryo stage, embryo quality, or interval from GnRH to ET (P&gt;0.10; Table 1). Pregnancies per ET (P/ET) on Day 60 were not different between the loading media groups, nor were there interactions between loading medium, embryo stage, and embryo quality, or interval from GnRH to ET (P&gt;0.10). Pregnancy loss between Days 32 and 60 was not different between groups, nor there were interactions between loading media groups and any other factor (P&gt;0.10). In conclusion, the use of either holding medium or SOFaaci-HEPES for fresh IVP embryo loading does not affect fertility; thus, both are suitable alternatives for loading of embryos into transfer straws.

Table 1.Pregnancies per embryo transfer (P/ET) and pregnancy loss in recipient heifers transferred with fresh invitro-produced embryos, using either holding medium or SOFaaci-HEPES medium for loading

Item
P/ET Day 32 (n)
P/ET Day 60 (n)
Pregnancy loss (n)

Loading medium

Holding
47.0% (186/396)
41.3% (163/395)
11.9% (22/185)

SOFaaci-HEPES
48.8% (197/404)
43.1% (174/404)
11.7% (23/197)

P-value
0.77
0.22
0.84