LAUSR

Objectives were to use meta-analytic approaches to compare slow-freezing (SF) and vitrification (VF) methods of cryopreservation on in-vitro (n = 12,211) and in-vivo (n = 3,473) survival of Bos taurus embryos. The literature was systematically reviewed and data from 40 manuscripts including 78 experiments, and comprising 183 treatment means, were used for the analyses. The in-vitro parameters included rates of re-expansion, hatching, and survival of blastocysts either at 24 h or 72 h post-thawing/warming and total number (TN) of embryonic cells, whereas in-vivo parameters evaluated embryonic survival between 35 - 60 d post embryo transfer (ET). Mixed models were fitted using MIXED and GLIMMIX procedures of SAS. Additionally, classical meta-analytical statistics were also fitted using METAN and METAREG procedures of STATA. The final models included the fixed effects of methods of cryopreservation and random effects of the experiment. Rates (LSM ± SEM) of re-expansion (0.36 ± 0.1 vs. 0.48 ± 0.1), hatching (0.25 ± 0.1 vs. 0.42 ± 0.1), and survival (0.57 ± 0.1 vs. 0.76 ± 0.1) at 72 h post-thawing/warming were lower (P < 0.05) in SF than VF, respectively. The TN of embryonic cells (96.9 ± 7.2 vs. 117.8 vs. 7.2) remained lower (P < 0.05) in SF than VF, however, the relative risk (RR) of embryonic survival post ET remained similar (RR = 1.0, CI = 0.8 - 1.2; P > 0.05) between both methods. Collectively, VF technique has a short-term protective effect against cryodamage of developing embryos, however, it might be dysregulating pregnancy success post ET in cows.